Abstract

Morbimortality due to infectious diarrheal diseases still is a serious health issue in Brazil and is highly related to factors such as weather, environment, and people’s life conditions. This study aimed to analyze the relationship between hospitalization rates due to infectious diarrheal diseases among the population of the municipality of Rio Branco (AC), Brazil and precipitation, river level, humidity and temperature between 2000 and 2013. Data were retrieved from the Hospital Information System of the SUS (Unified Health System), the National Institute of Meteorology and the National Water Agency. Multiple Poisson and negative binomial regression models were adjusted. Results showed that there is a positive association between hospitalization due to infectious diarrheal diseases and the level of the Acre river (RR: 1.07; CI 95%: 1.04 to 1.1); these hospitalization rates fell 14% between 2000 and 2013 (RR: 0.86; CI 95%: 0.85 to 0.87). The most vulnerable group was the age group of less than 1 year of age. This study showed the vulnerability of an Amazonian city to climate variability and its respective epidemiological influence on the incidence of hospitalizations due to infectious diarrheal diseases.

Key words
Diarrhea; Floods; Climate; Climate change; Amazonian ecosystem

Introduction

Infectious diarrheal diseases are caused by pathogens such as viruses, bacteria and protozoa, and their main physiological effects are dehydration and malnutrition¹1 Barreto ML, Teixeira MG, Bastos FI, Ximenes RAA, Barata RB, Rodrigues LC. Successes and failures in the control of infectious diseases in Brazil: social and environmental context, policies, interventions, and research needs. Lancet 2011; 377(9780):1877-1889.

2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^-33 Brandt KG, Antunes MMC, da Silva GAP. Acute diarrhea: evidence-based management. J Pediatr 2015; 91(6):36-43.. These diseases affect individuals of all age groups, but children are more vulnerable and susceptible to nutritional deficiencies that impair their growth, weight gain, intellectual development and even their survival²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,44 Morais MB, Fagundes Neto U. Enteropatia ambiental. Estudos avançados 2003; 17(48):137-149.

5 Gouvea VS, Dias GS, Aguiar EA, Pedro AR, Fichman ER, Chinem ES, Gomes SP, Domingues ALS. Acute Gastroenteritis in a Pediatric Hospital in Rio de Janeiro in Pre- and Post-Rotavirus Vaccination Settings. Open Virol J 2009; (3):26-30.

6 Coimbra Júnior CEA. Saúde e povos indígenas no Brasil: reflexões a partir do I Inquérito Nacional de Saúde e Nutrição Indígena. Cad Saude Publica 2014; 30(4):855-859.

7 Castro EDR, Germini MCBY, Mascarenhas JDP, Gabbay YB, Lima ICG, Lobo PS, Fraga VD, Conceição LM, Machado RLD, Rossit ARB. Enteropathogens detected in a Daycare Center, Southeastern Brazil: bacteria, virus, and parasite research. Rev. Inst. Med. Trop. São Paulo 2015; 57(1):27-32.^-88 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.. Diarrhea is among the leading causes of death in children under 5 years of age in poor countries, along with respiratory diseases. Morbimortality due to diarrhea is a public health problem in several regions of the world and is conditioned by several causes, but poverty, poor sanitation and climatic and environmental conditions favoring the transmission of pathogens are critical in the modulation, frequency and severity of this disease¹1 Barreto ML, Teixeira MG, Bastos FI, Ximenes RAA, Barata RB, Rodrigues LC. Successes and failures in the control of infectious diseases in Brazil: social and environmental context, policies, interventions, and research needs. Lancet 2011; 377(9780):1877-1889.

2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^-33 Brandt KG, Antunes MMC, da Silva GAP. Acute diarrhea: evidence-based management. J Pediatr 2015; 91(6):36-43.^,77 Castro EDR, Germini MCBY, Mascarenhas JDP, Gabbay YB, Lima ICG, Lobo PS, Fraga VD, Conceição LM, Machado RLD, Rossit ARB. Enteropathogens detected in a Daycare Center, Southeastern Brazil: bacteria, virus, and parasite research. Rev. Inst. Med. Trop. São Paulo 2015; 57(1):27-32.

8 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.^-99 Meneguessi GM, Mossri RM, Segatto TCV, Reis PO. Morbimortalidade por doenças diarreicas agudas em crianças menores de 10 anos no Distrito Federal, Brasil, 2003 a 2012. Epidemiol Serv. Saúde 2015; 24(3):721-730..

Deaths from diarrheal diseases remain high in Brazil, especially in children under 1 year of age and in the North and Northeast of the country²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,88 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.^,1010 Rufino R, Gracie R, Sena A, Freitas CM, Barcellos C. Surtos de diarreia na região Nordeste do Brasil em 2013, segundo a mídia e sistemas de informação de saúde - Vigilância de situações climáticas de risco e emergências em saúde. Cien Saude Colet 2016; 21(3):777-788.. Brazil has great demographic, economic, social, cultural and health diversity across its different regions. The North region comprises most of the Brazilian Amazon. In this vast region of humid tropical climate, climatic swings are intensified annually by floods that usually occur between October and April, which are favorable conditions for the spread of infectious diarrheal diseases²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,1111 Duarte AF, Mascarenhas MDM. Manifestações do bioclima do Acre sobre a saúde humana no contexto socioeconômico da Amazônia. Amazônia Ciência e Desenvolvimento 2007; 3:5.

12 Barcellos C, Monteiro AMV, Corvalán C, Gurgel HC, Carvalho MS, Artaxo P, Hacon S, Ragoni V. Mudanças climáticas e ambientais e as doenças infecciosas: Cenários e incertezas para o Brasil. Série Saúde ambiental 1; Brasília; 2008.

13 Victora CG. Diarrhea mortality: what can the world learn from Brazil? J Pediatr (Rio J) 2009; 85(1):3-5.

14 Duarte AF. As chuvas e as vazões na bacia hidrográfica do rio Acre, Amazônia Ocidental: Caracterização e implicações socioeconômicas e ambientais. Amazônia Ciência e desenvolvimento 2011; 6(12):161-183.^-1515 World Health Organization (WHO). Atlas of Heath and Climate. 2012. [acessado 2013 Nov 2]. Disponível em: http://www.who.int/globalchange/publications/atlas/report/en/
http://www.who.int/globalchange/publicat... . With the prospect of global climate change and the possibility of increased extreme weather events, special attention should be paid to the consequences to the health of this population, especially as the poor local urbanization conditions associated with the few advances in basic sanitation contribute to a typical vulnerability framework¹⁶16 Patz JA, Campbell-Lendrum D, Holloway T, Foley JA. Nature Impact of regional climate change on human health. Nature 2005; 438:310-317.

17 Haines A, Kovats RS, Campbell-Lendrum D, Corvalan C. Climate change and human health: impacts, vulnerability and public health. Public Health 2006; 120(7):585-596.

18 McMichael AJ, Woodruff RE, Hales S. Climate change and human health: present and future risks. Lancet 2006; 367(9513):859-869.

19 Confalonieri, UEC. Mudança climática global e saúde humana no Brasil. Parcerias Estratégicas 2008; 27.

20 Cartier R, Barcellos C, Hübner C, Porto MF. Vulnerabilidade social e risco ambiental: uma abordagem metodológica para avaliação de injustiça ambiental. Cad Saude Publica 2009; 25(12):2695-2704.

21 Freitas CM, Giatti LL. Environmental sustainability and health indicators in the Legal Amazonia, Brazil. Cad Saude Publica 2009; 25(6):1251-1266.^-2222 Silva DX, Barcellos C, Bacuri R. Vulnerabilidade e efeitos das mudanças climáticas na saúde pública em Manaus; 2010. [acessado 2014 Out 15]. Disponível em: https://www.researchgate.net/publication/267756918_Natural_disasters_and_health_An_analysis_of_the_situation_in_Brazil/fulltext/55ee3e0908aedecb68fc823f/267756918_Natural_disasters_and_health_An_analysis_of_the_situation_in_Brazil.pdf?origin=publication_detail
https://www.researchgate.net/publication... .

Thus, this ecological study aimed to analyze the association of hospitalization rates due to infectious diarrheal diseases in the population of the municipality of Rio Branco, capital of the state of Acre, with climatic variables such as precipitation, Acre River’s level, humidity and temperature in the period 2000-2013. This type of study is fundamental for the region, as it contributes to a better knowledge about the climate-health relationship and may subsidize the elaboration of public policies aimed at improving the indicators of this health problem and the quality of life of the population in general. We also sought to study the behavior of these hospitalization rates in terms of their temporal trend and in different age groups, in order to increase the epidemiological knowledge of these diseases at the local level.

Methodology

The study area was the municipality of Rio Branco, capital of the state of Acre, located in the Western Amazon region of northern Brazil. According to IBGE (2016), the municipality has a population of approximately 370 thousand inhabitants and a predominantly hot and humid tropical climate; temperatures remain around 25-30ºC all year round, with short cooling periods, where temperatures usually drop to around 14ºC. The adjusted mean relative humidity remains higher than most other regions of the country throughout the year, with percentages usually above 65%¹¹11 Duarte AF, Mascarenhas MDM. Manifestações do bioclima do Acre sobre a saúde humana no contexto socioeconômico da Amazônia. Amazônia Ciência e Desenvolvimento 2007; 3:5.^,1414 Duarte AF. As chuvas e as vazões na bacia hidrográfica do rio Acre, Amazônia Ocidental: Caracterização e implicações socioeconômicas e ambientais. Amazônia Ciência e desenvolvimento 2011; 6(12):161-183.^,2323 Instituto Nacional de Meteorologia (INMET). Banco de dados meteorológicos para ensino e pesquisa. [acessado 2014 Fev 13]. Disponível em: http://www.inmet.gov.br/portal/index.php?r=bdmep/bdmep
http://www.inmet.gov.br/portal/index.php... .

The municipality developed on the banks of the Acre River, one of the largest rivers in the North, which springs from Peru and flows into Brazil across the state. In rainy periods, which usually occur between the months of October and April, the river level rises and most often exceeds its alert level for overflow (13.5 meters), which causes the flooding of much of the city¹¹11 Duarte AF, Mascarenhas MDM. Manifestações do bioclima do Acre sobre a saúde humana no contexto socioeconômico da Amazônia. Amazônia Ciência e Desenvolvimento 2007; 3:5.^,1414 Duarte AF. As chuvas e as vazões na bacia hidrográfica do rio Acre, Amazônia Ocidental: Caracterização e implicações socioeconômicas e ambientais. Amazônia Ciência e desenvolvimento 2011; 6(12):161-183.. The seasonal pattern of rainfall in the state is regular. High floods in the Amazonian winter are predictable, but the disordered occupation of the flood plains favors the occurrence of flooding. According to a study carried out by Duarte²⁴24 Duarte AF. A vulnerabilidade social como causa fundamental das alagações recorrentes no estado do Acre, Amazônia Ocidental. 2015. [acessado 2014 Fev 13]. Disponível em: http://www.acrebioclima.net/p19upb1cbga5d1il610k3p3n7rn5.pdf
http://www.acrebioclima.net/p19upb1cbga5... , urban settlements were located in the flood plains of the Acre River in the municipalities of Rio Branco, Assis Brasil, Brasileia and Xapuri. The study also points out that 79.1% of the population growth in the state has been converted into socially vulnerable residents who are exposed to the environment of waters along riverbanks, streams and sewage pipes²⁴24 Duarte AF. A vulnerabilidade social como causa fundamental das alagações recorrentes no estado do Acre, Amazônia Ocidental. 2015. [acessado 2014 Fev 13]. Disponível em: http://www.acrebioclima.net/p19upb1cbga5d1il610k3p3n7rn5.pdf
http://www.acrebioclima.net/p19upb1cbga5... .

In addition, the state of Acre is described in the literature as one with the worst sanitation indicators in Brazil²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,2525 Trata Brasil. 2014. [acessado 2017 Jan 19]. Disponível em: http://www.tratabrasil.org.br/datafiles/estudos/ranking/tabela-100-cidades2014.pdf
http://www.tratabrasil.org.br/datafiles/... . In 2014, Rio Branco was among the 15 largest municipalities in the country with the worst sanitation, with more than 78% of the population without access to sewage collection and just over half of the population covered by the water supply system²⁵25 Trata Brasil. 2014. [acessado 2017 Jan 19]. Disponível em: http://www.tratabrasil.org.br/datafiles/estudos/ranking/tabela-100-cidades2014.pdf
http://www.tratabrasil.org.br/datafiles/... . The capital also has high percentage of indigenous population living in rural areas and with less access to these services²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,66 Coimbra Júnior CEA. Saúde e povos indígenas no Brasil: reflexões a partir do I Inquérito Nacional de Saúde e Nutrição Indígena. Cad Saude Publica 2014; 30(4):855-859.^,2626 Instituto Brasileiro de Geografia e Estatística (IBGE). Censo Demográfico 2010. Resultados Preliminares do Universo. Rio de Janeiro: IBGE; 2010. [acessado 2014 Set 17]. Disponível em: < http://www.ibge.gov.br/home/estatistica/populacao/censo2010/resultados_preliminares_amostra/notas_resultados_preliminares_amostra.pdf
http://www.ibge.gov.br/home/estatistica/... ^,2727 Paim J, Travassos C, Almeida C, Bahia L, Macinko J. O sistema de saúde brasileiro: história, avanços e desafios. Lancet 2011; 1:11-31.. It is important to emphasize that the North is the second poorest region of the country and has one of the highest incidence rates of diarrheal diseases in children under 5 years of age, after the Northeast²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742..

For this study, we used data on the number of monthly hospitalizations due to infectious diarrheal diseases, categorized by age group, obtained between January 1, 2000 and December 31, 2013. This information was extracted from the Hospital Information System of the Unified Health System (SIH/SUS), available on the website of the Department of Information Technology of the SUS maintained by the Brazilian Ministry of Health²⁹29 Departamento de Informática do SUS. Sistema de Informações Hospitalares. [acessado 2014 Abr 4]. Disponível em: http://www2.datasus.gov.br/DATASUS/index.php?area=0203&id=6926
http://www2.datasus.gov.br/DATASUS/index... . Hospitalization case records were used under codes A03 (Shigellosis), A06 (Amebiasis), A09 (Infectious gastroenteritis and colitis, unspecified), A00 (Cholera), A01 (Typhoid and paratyphoid fevers) and Z22.1 (Carrier of other intestinal infectious diseases) of the 10^th Review of the International Classification of Diseases (ICD-10).

The climatic variables used for the association studies were monthly average of total precipitation (in mm); average monthly maximum temperature (in ºC); average monthly adjusted temperature (in ºC); average monthly minimum temperature (in ºC); mean monthly average relative humidity (in %); and monthly average of the Acre River’s level (in meters). These data were extracted from the information database available on the website of the National Institute of Meteorology²³23 Instituto Nacional de Meteorologia (INMET). Banco de dados meteorológicos para ensino e pesquisa. [acessado 2014 Fev 13]. Disponível em: http://www.inmet.gov.br/portal/index.php?r=bdmep/bdmep
http://www.inmet.gov.br/portal/index.php... and from the hydrological information system available on the website of the National Water Agency³⁰30 Agência Nacional das Águas (ANA). Sistema de informações hidrológicas. [acessado 2014 Mar 18]. Disponível em: http://www2.ana.gov.br/Paginas/servicos/informacoeshidrologicas/redehidro.aspx
http://www2.ana.gov.br/Paginas/servicos/... .

All data from this research were retrieved from open access secondary sources, waiving the Research Ethics Committee’s scrutiny and approval. This information was tabulated and organized into Microsoft Excel spreadsheets. The mean monthly hospitalization rates due to infectious diarrheal diseases per 100,000 inhabitants and their variance were calculated, which were stratified according to year and age group. The population estimates for the years of the analysis period (2000-2013) were obtained from the Brazilian Institute of Geography and Statistics Foundation²⁶26 Instituto Brasileiro de Geografia e Estatística (IBGE). Censo Demográfico 2010. Resultados Preliminares do Universo. Rio de Janeiro: IBGE; 2010. [acessado 2014 Set 17]. Disponível em: < http://www.ibge.gov.br/home/estatistica/populacao/censo2010/resultados_preliminares_amostra/notas_resultados_preliminares_amostra.pdf
http://www.ibge.gov.br/home/estatistica/... .

Generalized Linear Models (GLM) were used to estimate the association between climatic and environmental variables and the rate of hospitalizations due to diarrheal diseases. The analyzes were performed using the Stata statistical software (Data Analysis and Statistical Software) version 13.0³¹31 StataCorp. Stata Statistical Software: Release 13. College Station: StataCorp LP; 2013. (permission of use granted to the Faculty of Public Health of the University of São Paulo).

The rate ratios (RR) were calculated, which were initially adjusted using the Poisson regression and the negative binomial (NB) regression model, both estimated by maximum likelihood, as the alternative³²32 Khan A, Ullah S, Nitz J. Statistical modelling of falls count data with excess zeros. Injury Prevention 2011; 17(4):266-270.

33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^-3434 Lee Y, Nelder JA. Hierarchical generalized linear models: a synthesis of generalized linear models, random-effect models and structured dispersions. Biometrika 2001; 88:987-1006.. Adjustments of the models obtained with BN regression were evaluated by analyzing the statistical significance of the alpha (α) value. When the value obtained was significantly different from zero, then the multiple BN regression model was adopted to obtain the adjusted estimates, considering overdispersed data³²32 Khan A, Ullah S, Nitz J. Statistical modelling of falls count data with excess zeros. Injury Prevention 2011; 17(4):266-270.

33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^-3434 Lee Y, Nelder JA. Hierarchical generalized linear models: a synthesis of generalized linear models, random-effect models and structured dispersions. Biometrika 2001; 88:987-1006..

When choosing variables, we considered the statistical significance of the parameters, the McFadden’s pseudo-R²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140. increase and the confidence intervals for the significance level of 5%³²32 Khan A, Ullah S, Nitz J. Statistical modelling of falls count data with excess zeros. Injury Prevention 2011; 17(4):266-270.

33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^-3434 Lee Y, Nelder JA. Hierarchical generalized linear models: a synthesis of generalized linear models, random-effect models and structured dispersions. Biometrika 2001; 88:987-1006.. Variables whose parameters were not statistically different from zero at the significance level of 5% were discarded from the analyses using the stepwise procedure that, in several modeling software, has the property of automatically excluding the explanatory variables whose parameters are not statistically different from zero³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.. This procedure was also used to correct the multicollinearity between the explanatory variables³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015..

The final model was evaluated using the deviance and Pearson’s statistical tests for the goodness-of-fit³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^,3535 Cameron AC, Trivedi PK. Microeconometrics using Stata Revised edition. College Station: Stata Press; 2009. and contains all parameters statistically different from zero at the significance level of 5%, with the highest adjusted R²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140. value and with less amplitude of the confidence intervals. The quality of fit was measured by the Chi-square test (X²) to compare the two curves and the lack of statistically significant differences between predicted and observed values³²32 Khan A, Ullah S, Nitz J. Statistical modelling of falls count data with excess zeros. Injury Prevention 2011; 17(4):266-270.

33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^-3434 Lee Y, Nelder JA. Hierarchical generalized linear models: a synthesis of generalized linear models, random-effect models and structured dispersions. Biometrika 2001; 88:987-1006..

Results

In these 14 years, 8,080 hospitalizations due to infectious diarrheal diseases in the population of the city of Rio Branco were recorded in the DATASUS database, and 1,153 hospitalizations were recorded in 2006 alone. Rates monthly average were 16.5 hospitalizations and variance of 147.9.

Due to the large difference between the mean and variance values, we decided to adopt the negative binomial regression model for the analyses.³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015. Furthermore, the fit quality of data obtained with the Poisson distribution showed significant differences between the observed and predicted values (p < 0.001). On the other hand, the alpha (α) term value of the model with negative binomial distribution was significantly different from zero (Table 1), which indicated that this is the most adequate model for analysis, considering overdispersed data³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015..

Variables whose parameters were not statistically different from zero at the significance level of 5%, after the application of the stepwise procedure³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015. were discarded from the analysis, leaving out the following variables: river’s level, mean relative humidity, year and age group.

The results of this study show that there is a significant positive association between hospitalization rates due to infectious diarrheal diseases and the Rio Acre level, with a 7% increase in these rates for each meter of river level increase (RR: 1.07; 95% CI: 1.04 to 1.1). In addition, there is a negative relationship between hospitalization rates and years, with a general decline of 14% in hospitalization rates due to these diseases between the years 2000 and 2013 (RR: 0.86, 95% CI: 0.85-0.87), as well as a negative association between hospitalization rates and adjusted mean relative humidity (RR: 0.97; 95% CI: 0.96 to 0.99), (Table 1).

The Graph 1 shows that, over the years, in general, hospitalization rates have decreased in the period 2000-2013. However, some increases were recorded during this period in specific years. At first, rates fell between 2000 and 2004. From then on, a sudden upswing was recorded until 2006, when the highest rates of hospitalizations due to diarrheal diseases of the period were recorded. In the following years, rates declined progressively until 2009, when a slight elevation was recorded. Thereafter, rates declined steadily until 2013, when the lowest rates of hospitalizations due to infectious diarrheal diseases of the period studied were recorded.

The age group with the highest hospitalization rates includes children under 1 year of age followed by children 1 to 4 years of age. High hospitalization rates were also found in the elderly group, especially for those over 70 years of age (Chart 2).

Discussion

Results obtained in this study evidenced a significant association between the rates of hospitalization due to diarrheal diseases and the Acre River level, year, adjusted mean relative humidity and age group. Poisson Regression³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^,3636 Davies GI, McIver L, Kim Y, Hashizume M, Iddings S, Chan V. Water-Borne Diseases and Extreme Weather Events in Cambodia: Review of Impacts and Implications of Climate Change. Int. J. Environ Res. Public Health 2015; 12(1):191-213. is usually adopted as a standard for analyses containing this data type. However, this model assumes equality between mean and variance, which does not always occur in series with overdispersion or excess of zeros. In these cases, the use of Poisson regression may lead to an underestimation of coefficient standard errors, very narrow confidence intervals and small p-values³²32 Khan A, Ullah S, Nitz J. Statistical modelling of falls count data with excess zeros. Injury Prevention 2011; 17(4):266-270.^,3333 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.. The negative binomial distribution has a modified variance function that makes its dispersion parameter facilitate the accommodation of an extra variation and bypass the issue³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015.^,3434 Lee Y, Nelder JA. Hierarchical generalized linear models: a synthesis of generalized linear models, random-effect models and structured dispersions. Biometrika 2001; 88:987-1006.. Once this last model has been tested, the alpha value found shows an overdispersion that must be taken into account and, thus, this was the analytical model adopted in this research³³33 Fávero LP. Análise de dados. Rio de janeiro: Elsevier; 2015..

The results obtained with the analyses of this study show, for the first time in this municipality, how the river level can interfere in the monthly hospitalization rates due to infectious diarrheal diseases. The model shows that each meter increase in the monthly average of the Acre River level can contribute to a 7% hike in these rates. This variable is an indicator for the prediction of trends in the occurrence of this disease in this municipality and in the other municipalities of the Amazon region, as they share similar climatic and environmental features²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.. Graph 3 shows the time series of these variables during the study period.

Outbreaks of diarrhea associated with extreme weather events have occurred worldwide, especially after flooding events and inundations⁹9 Meneguessi GM, Mossri RM, Segatto TCV, Reis PO. Morbimortalidade por doenças diarreicas agudas em crianças menores de 10 anos no Distrito Federal, Brasil, 2003 a 2012. Epidemiol Serv. Saúde 2015; 24(3):721-730.^,2828 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.^,3636 Davies GI, McIver L, Kim Y, Hashizume M, Iddings S, Chan V. Water-Borne Diseases and Extreme Weather Events in Cambodia: Review of Impacts and Implications of Climate Change. Int. J. Environ Res. Public Health 2015; 12(1):191-213.

37 Harris AM, Chowdhury F, Begum YA, Khan AI, Faruque ASG, Svennerholm AM, Harris JB, Ryan ET, Cravioto A, Calderwood SB, Qadri F. Shifting Prevalence of Major Diarrheal Pathogens in Patients Seeking Hospital Care during Floods in 1998, 2004, and 2007 in Dhaka, Bangladesh. Am J. Trop. Med. Hyg 2008; 79(5):708-714.

38 Ding G, Zhang Y, Gao L, Ma W, Li X, Liu J, Liu Q, Jiang B. Quantitative Analysis of Burden of Infectious Diarrhea Associated with Floods in Northwest of Anhui Province, China: A Mixed Method Evaluation. PLoS One 2013; 8(6):1-9.

39 Jones FK, Ko AI, Becha C, Joshua C, Musto J, Thomas S, Ronsse A, Kirkwood CD, Sio A, Aumua A, Nilles EJ. Increased Rotavirus Prevalence in Diarrheal Outbreak Precipitated by Localized Flooding, Solomon Islands, 2014. Emerging Infectious Diseases 2016; 22(5):875-879.

40 Wakuma Abaya S, Mandere N, Ewald G. Floods and health in Gambella region, Ethiopia: a qualitative assessment of the strengths and weaknesses of coping mechanisms. Glob Health Action 2009; 2:1-10.^-4141 Bokhari H, Shah MA, Asad S, Akhtar S, Akram M, Wren BW. Escherichia coli Pathotypes in Pakistan from Consecutive Floods in 2010 and 2011. Am. J. Trop. Med. Hyg 2013; 88(3):519-525.. However, until then, no one knew how much these factors could contribute to the occurrence of infectious diarrheal diseases in this municipality with potential to cause hospitalization. In Rio Branco, this situation is now a matter of great concern, because Acre River’s floods occur practically every year, lead to seasonal flooding of the lowland areas characteristic of the Amazonian geography and inundate a large part of the city, which may contribute to transmission and contagion by these diseases²⁴24 Duarte AF. A vulnerabilidade social como causa fundamental das alagações recorrentes no estado do Acre, Amazônia Ocidental. 2015. [acessado 2014 Fev 13]. Disponível em: http://www.acrebioclima.net/p19upb1cbga5d1il610k3p3n7rn5.pdf
http://www.acrebioclima.net/p19upb1cbga5... ^,4343 D'Aguila PS, Roque OCC, Miranda CAS, Ferreira AP. Avaliação da qualidade de água para abastecimento público do Município de Nova Iguaçu. Cad Saude Publica 2000; 16(3):791-798..

In Rio Branco, Acre River’s flooding almost always occur in the February-April period, putting thousands of families at risk in several cities. In 2006, some 29,000 people were affected by one of the river’s major floods. In March 2010, more than 4,000 buildings were affected, with more than 350 displaced and homeless families. In 2012, more than 6,000 people were left homeless, and this was the second largest flood since the beginning of the Acre River’s level measurements. In 2015, the largest flood ever recorded in state history left more than 9,000 people homeless²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.^,4343 D'Aguila PS, Roque OCC, Miranda CAS, Ferreira AP. Avaliação da qualidade de água para abastecimento público do Município de Nova Iguaçu. Cad Saude Publica 2000; 16(3):791-798..

During floods, the water distribution network for human consumption may be affected, compromising the supply system for homes and health services, resulting in lack of drinking water or distribution of water contaminated by infectious agents³⁶36 Davies GI, McIver L, Kim Y, Hashizume M, Iddings S, Chan V. Water-Borne Diseases and Extreme Weather Events in Cambodia: Review of Impacts and Implications of Climate Change. Int. J. Environ Res. Public Health 2015; 12(1):191-213.^,3838 Ding G, Zhang Y, Gao L, Ma W, Li X, Liu J, Liu Q, Jiang B. Quantitative Analysis of Burden of Infectious Diarrhea Associated with Floods in Northwest of Anhui Province, China: A Mixed Method Evaluation. PLoS One 2013; 8(6):1-9.^,4343 D'Aguila PS, Roque OCC, Miranda CAS, Ferreira AP. Avaliação da qualidade de água para abastecimento público do Município de Nova Iguaçu. Cad Saude Publica 2000; 16(3):791-798.

44 Noji EK. The Public Health Consequences of Disaster. Prehosp Disaster Med 2000; 15(4):147-157.

45 Euripidou E, Murray V. Public health impacts of floods and chemical contamination. J Public Health (Oxf) 2004; 26(4):376-383.

46 Freitas CM, Ximenes EF. Floods and public health: a review of the recent scientific literature on the causes, consequences and responses to prevention and mitigation. Cien Saude Colet 2012; 17(6):1601-1615.^-4747 Oliveira BSS, Cunha AC. Correlação entre qualidade da água e variabilidade da precipitação no sul do Estado do Amapá. Ambiente & Água 2014; 9(2):261-275.. Food stored in homes or markets may be contaminated by biological agents and by chemical products of industrial, commercial and/or residential origin. In these periods, other urban and basic sanitation services, such as sewage collection and waste disposal are also affected, favoring conditions for the emergence and spread of diseases²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.^,3939 Jones FK, Ko AI, Becha C, Joshua C, Musto J, Thomas S, Ronsse A, Kirkwood CD, Sio A, Aumua A, Nilles EJ. Increased Rotavirus Prevalence in Diarrheal Outbreak Precipitated by Localized Flooding, Solomon Islands, 2014. Emerging Infectious Diseases 2016; 22(5):875-879.^,4747 Oliveira BSS, Cunha AC. Correlação entre qualidade da água e variabilidade da precipitação no sul do Estado do Amapá. Ambiente & Água 2014; 9(2):261-275.

48 Ivers LC, Ryan ET. Infectious diseases of severe weather-related and flood-related natural disasters. Current Opinion in Infectious Disease 2006; 19(5):408-414.

49 George P. Health impacts of floods. Prehosp Disaster Med. 2011; 26(2):137.^-5050 Taylor J, Lai KM, Davies M, Clifton D, Ridley I, Biddulph P. Flood management: prediction of microbial contamination in large-scale floods in urban environments. Environ Int. 2011; 37(5):1019-1029..

Another consequence of floods and inundations is change in the reproductive cycles of vectors, hosts and reservoirs of diseases due to the proliferation of wastewater, garbage and decomposing materials on the streets, leading to an increased number of mosquitoes, flies, rats, and fecal environmental contamination by parasites. Thus, the sources of exposure to the risk of diseases increase, especially for those who are displaced or become homeless⁴⁶46 Freitas CM, Ximenes EF. Floods and public health: a review of the recent scientific literature on the causes, consequences and responses to prevention and mitigation. Cien Saude Colet 2012; 17(6):1601-1615.^,5050 Taylor J, Lai KM, Davies M, Clifton D, Ridley I, Biddulph P. Flood management: prediction of microbial contamination in large-scale floods in urban environments. Environ Int. 2011; 37(5):1019-1029.

51 Kunii O, Nakamura S, Abdur R, Wakai S. The impact on health and risk factors of the diarrhoea epidemics in the 1998 Bangladesh floods. Public Health 2002; 116(2):68-74.^-5252 Du W, FitzGerald GJ, Clark M, Hou XY. Health impacts of floods. Prehosp Disaster Med .2010; 25(3):265-272..

Massive population displacement, crowding in shelters and the accelerated and poor urbanization process also create conditions for the spread of communicable diseases²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.. When this process tends to occur with improper planning, the construction of water supply networks and sewage collection, for example, is adopted as a measure of adaptation and develops for domestic supply, but these improvements are vulnerable to environmental changes due to the easy contamination and also by inadequate water treatment and distribution capacity⁸8 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.^,1515 World Health Organization (WHO). Atlas of Heath and Climate. 2012. [acessado 2013 Nov 2]. Disponível em: http://www.who.int/globalchange/publications/atlas/report/en/
http://www.who.int/globalchange/publicat... ^,2222 Silva DX, Barcellos C, Bacuri R. Vulnerabilidade e efeitos das mudanças climáticas na saúde pública em Manaus; 2010. [acessado 2014 Out 15]. Disponível em: https://www.researchgate.net/publication/267756918_Natural_disasters_and_health_An_analysis_of_the_situation_in_Brazil/fulltext/55ee3e0908aedecb68fc823f/267756918_Natural_disasters_and_health_An_analysis_of_the_situation_in_Brazil.pdf?origin=publication_detail
https://www.researchgate.net/publication... .

In fact, the intense urbanization of the Brazilian Amazon region has been under pressure in recent decades due to the increased migration, which has aggravated the situation of poverty in the region. In Rio Branco, for example, as in other cities in the region, urban settlements are common in rivers’ flood plains because of this process. This results in increased socially and environmentally vulnerable population that is exposed to various flood damages¹⁵15 World Health Organization (WHO). Atlas of Heath and Climate. 2012. [acessado 2013 Nov 2]. Disponível em: http://www.who.int/globalchange/publications/atlas/report/en/
http://www.who.int/globalchange/publicat... ^,2222 Silva DX, Barcellos C, Bacuri R. Vulnerabilidade e efeitos das mudanças climáticas na saúde pública em Manaus; 2010. [acessado 2014 Out 15]. Disponível em: https://www.researchgate.net/publication/267756918_Natural_disasters_and_health_An_analysis_of_the_situation_in_Brazil/fulltext/55ee3e0908aedecb68fc823f/267756918_Natural_disasters_and_health_An_analysis_of_the_situation_in_Brazil.pdf?origin=publication_detail
https://www.researchgate.net/publication... ^,2424 Duarte AF. A vulnerabilidade social como causa fundamental das alagações recorrentes no estado do Acre, Amazônia Ocidental. 2015. [acessado 2014 Fev 13]. Disponível em: http://www.acrebioclima.net/p19upb1cbga5d1il610k3p3n7rn5.pdf
http://www.acrebioclima.net/p19upb1cbga5... .

Such environmental conditions have also contributed to the occurrence of other diseases in the region, especially dengue and leptospirosis, which have accounted for an elevated number of victims in the region, with increasingly severe symptoms¹1 Barreto ML, Teixeira MG, Bastos FI, Ximenes RAA, Barata RB, Rodrigues LC. Successes and failures in the control of infectious diseases in Brazil: social and environmental context, policies, interventions, and research needs. Lancet 2011; 377(9780):1877-1889.^,2929 Departamento de Informática do SUS. Sistema de Informações Hospitalares. [acessado 2014 Abr 4]. Disponível em: http://www2.datasus.gov.br/DATASUS/index.php?area=0203&id=6926
http://www2.datasus.gov.br/DATASUS/index... . In Rio Branco, in the same period, more than 80,000 cases of dengue have been reported and confirmed by the Epidemiological Surveillance Department of the Municipal Health Secretariat²⁹29 Departamento de Informática do SUS. Sistema de Informações Hospitalares. [acessado 2014 Abr 4]. Disponível em: http://www2.datasus.gov.br/DATASUS/index.php?area=0203&id=6926
http://www2.datasus.gov.br/DATASUS/index... . In addition, respiratory diseases have also generated increasing concern at the local level, since they mainly involve children, similarly to infectious diarrheal diseases¹1 Barreto ML, Teixeira MG, Bastos FI, Ximenes RAA, Barata RB, Rodrigues LC. Successes and failures in the control of infectious diseases in Brazil: social and environmental context, policies, interventions, and research needs. Lancet 2011; 377(9780):1877-1889.^,1515 World Health Organization (WHO). Atlas of Heath and Climate. 2012. [acessado 2013 Nov 2]. Disponível em: http://www.who.int/globalchange/publications/atlas/report/en/
http://www.who.int/globalchange/publicat... ^,2929 Departamento de Informática do SUS. Sistema de Informações Hospitalares. [acessado 2014 Abr 4]. Disponível em: http://www2.datasus.gov.br/DATASUS/index.php?area=0203&id=6926
http://www2.datasus.gov.br/DATASUS/index... .

In addition, with the prospect of global climate change, it is believed that the risk of extreme events may become more frequent in the future. Climatic models designed for the Amazon rainforest point to increasingly elevated temperature, which may influence the rainfall regime and floods events in the region²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.^,5353 Marengo JA, Borma LS, Rodriguez DA, Pinho P, Soares WR, Alves LM. Recent Extremes of Drought and Flooding in Amazonia: Vulnerabilities and Human Adaptation. Am J. Clim Change 2013; 2:87-96.^,5454 Intergovernmental Panel on Climate Change (IPCC). [acessado 2015 Abr 14]. Disponível em: http://www.ipcc.ch
http://www.ipcc.ch... . The great Amazonian floods in this century resulted from unusually strong precipitations in northern Brazil and were generally associated with higher than normal surface temperatures of the Tropical South Atlantic Ocean⁵³53 Marengo JA, Borma LS, Rodriguez DA, Pinho P, Soares WR, Alves LM. Recent Extremes of Drought and Flooding in Amazonia: Vulnerabilities and Human Adaptation. Am J. Clim Change 2013; 2:87-96.

54 Intergovernmental Panel on Climate Change (IPCC). [acessado 2015 Abr 14]. Disponível em: http://www.ipcc.ch
http://www.ipcc.ch...

55 Fonseca PAM, Veiga JP, Correia FS, Brito A, Queiroz M, Lyra A, Chan SC. Projecting Extreme Changes in Summer Rainfall in South America by the Middle of the 21st Century. Atmos Clim. Sci. 2014; 4(4):743-756.^-5656 Valverde MC, Marengo JA. Extreme Rainfall Indices in the Hydrographic Basins of Brazil. Open Journal of Modern Hydrology 2014; 4(1):10-26..

Interestingly, the results of this study showed a negative, albeit small association between the monthly average of the adjusted mean relative humidity and rates of hospitalization due to infectious diarrheal diseases. However, this result may have been achieved to the detriment of peculiarities of the climate of this region, which is quite hot and humid. The lowest value for the monthly average of relative humidity obtained in the city during the study period was 67.25%, while the highest value was 92.30%, which reflects the high humidity and the small variation²³23 Instituto Nacional de Meteorologia (INMET). Banco de dados meteorológicos para ensino e pesquisa. [acessado 2014 Fev 13]. Disponível em: http://www.inmet.gov.br/portal/index.php?r=bdmep/bdmep
http://www.inmet.gov.br/portal/index.php... . Thus, periods of marked increases or decreases in the rate of hospitalization due to infectious diarrheal diseases were not accompanied by such sharp increases or decreases in relative humidity, which is measured as a percentage (Graph 4). Therefore, this variable was not considered adequate for this type of study.

Regarding the behavior of rates of hospitalization due to diarrheal diseases over time in this municipality, the statistical model showed a declining trend, especially after 2006. One of the main explanations for this result refers to the introduction of the rotavirus vaccine in the SUS vaccination calendar. Since 2006, Brazil has immunized children in the first two years of life against this pathogen by an attenuated oral vaccine⁵5 Gouvea VS, Dias GS, Aguiar EA, Pedro AR, Fichman ER, Chinem ES, Gomes SP, Domingues ALS. Acute Gastroenteritis in a Pediatric Hospital in Rio de Janeiro in Pre- and Post-Rotavirus Vaccination Settings. Open Virol J 2009; (3):26-30.^,99 Meneguessi GM, Mossri RM, Segatto TCV, Reis PO. Morbimortalidade por doenças diarreicas agudas em crianças menores de 10 anos no Distrito Federal, Brasil, 2003 a 2012. Epidemiol Serv. Saúde 2015; 24(3):721-730.. In the literature, rotavirus has been highlighted as one of the most prevalent pathogens causing severe diarrhea with severe dehydration and need for hospitalization after floods⁵5 Gouvea VS, Dias GS, Aguiar EA, Pedro AR, Fichman ER, Chinem ES, Gomes SP, Domingues ALS. Acute Gastroenteritis in a Pediatric Hospital in Rio de Janeiro in Pre- and Post-Rotavirus Vaccination Settings. Open Virol J 2009; (3):26-30.^,3838 Ding G, Zhang Y, Gao L, Ma W, Li X, Liu J, Liu Q, Jiang B. Quantitative Analysis of Burden of Infectious Diarrhea Associated with Floods in Northwest of Anhui Province, China: A Mixed Method Evaluation. PLoS One 2013; 8(6):1-9.^,3939 Jones FK, Ko AI, Becha C, Joshua C, Musto J, Thomas S, Ronsse A, Kirkwood CD, Sio A, Aumua A, Nilles EJ. Increased Rotavirus Prevalence in Diarrheal Outbreak Precipitated by Localized Flooding, Solomon Islands, 2014. Emerging Infectious Diseases 2016; 22(5):875-879.. Thus, immunization against rotavirus and universal coverage were an important contribution in the reduction of severe forms, in the number of hospitalizations and in the risk of death from this disease, as shown by some studies carried out in Brazil and in other countries³3 Brandt KG, Antunes MMC, da Silva GAP. Acute diarrhea: evidence-based management. J Pediatr 2015; 91(6):36-43.^,55 Gouvea VS, Dias GS, Aguiar EA, Pedro AR, Fichman ER, Chinem ES, Gomes SP, Domingues ALS. Acute Gastroenteritis in a Pediatric Hospital in Rio de Janeiro in Pre- and Post-Rotavirus Vaccination Settings. Open Virol J 2009; (3):26-30.^,99 Meneguessi GM, Mossri RM, Segatto TCV, Reis PO. Morbimortalidade por doenças diarreicas agudas em crianças menores de 10 anos no Distrito Federal, Brasil, 2003 a 2012. Epidemiol Serv. Saúde 2015; 24(3):721-730.^,5757 Guevara JN, López O, González G. Impacto de la introdución de la vacuna contra el rotavirus en la hospitalización por gastroenteritis aguda grave en el Hospital del Nino de la Ciudad de Panamá. Am J Public Health 2008; 24(3):189-194.^,5858 Masukawa MLT, Moriwaki AM, Uchimura NS, Souza EM, Uchimura TT. Intervention analysis of introduction of rotavirus vaccine on hospital admissions rates due to acute diarrhea. Cad Saude Publica 2014; 30(10):2101-2111..

Other factors contributing to this situation include improvements in sanitation conditions, water quality, campaigns to encourage total and exclusive breastfeeding duration, reduced prevalence of malnutrition and improved access to health care with increased vaccination coverage against measles and the use of oral rehydration²⁰20 Cartier R, Barcellos C, Hübner C, Porto MF. Vulnerabilidade social e risco ambiental: uma abordagem metodológica para avaliação de injustiça ambiental. Cad Saude Publica 2009; 25(12):2695-2704.^,2121 Freitas CM, Giatti LL. Environmental sustainability and health indicators in the Legal Amazonia, Brazil. Cad Saude Publica 2009; 25(6):1251-1266.^,5959 Santos FS, Santos LH, Saldan PC, Santos FCS, Leite AM, Mello DF. Aleitamento materno e diarreia aguda entre crianças cadastradas na Estratégia Saúde da Família. Texto Contexto Enferm. 2016; 25(1):1-8.. The expanded Family Health Strategy (ESF) and the establishment of social programs, such as the Bolsa Família and the Mais Médicos Program, for example, contributed in recent years to a substantial increase in access to PHC and quality of life of the population⁵⁹59 Santos FS, Santos LH, Saldan PC, Santos FCS, Leite AM, Mello DF. Aleitamento materno e diarreia aguda entre crianças cadastradas na Estratégia Saúde da Família. Texto Contexto Enferm. 2016; 25(1):1-8.

60 Soares, SSD. Bolsa Família, its design, its impacts and possibilities for the future. International Policy Centre for Inclusive Growth 2012; 89.^-6161 Gonçalves RF, Sousa IMC, Tanaka OU, Santos CR, Brito-Silva K, Santos LX, Bezerra AFB. Programa Mais Médicos no Nordeste: avaliação das internações por condições sensíveis à Atenção Primária à Saúde. Cien Saude Colet 2016; 21(9):2815-2824..

However, despite advances, infectious diarrheal diseases are still a serious public health problem in Brazil and generate high hospitalization rates, especially in children under 1 year, as shown in the results of this study and in several other studies²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,88 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.^,6161 Gonçalves RF, Sousa IMC, Tanaka OU, Santos CR, Brito-Silva K, Santos LX, Bezerra AFB. Programa Mais Médicos no Nordeste: avaliação das internações por condições sensíveis à Atenção Primária à Saúde. Cien Saude Colet 2016; 21(9):2815-2824.. In addition, childhood diarrhea appears as a disease that evidences health inequity in the Brazilian territory. Health indicators show the highest rates of morbimortality in the North and Northeast regions, which have the worst conditions of poverty and basic sanitation in Brazil²2 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140.^,88 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.^,6161 Gonçalves RF, Sousa IMC, Tanaka OU, Santos CR, Brito-Silva K, Santos LX, Bezerra AFB. Programa Mais Médicos no Nordeste: avaliação das internações por condições sensíveis à Atenção Primária à Saúde. Cien Saude Colet 2016; 21(9):2815-2824..

We should also consider that more information about the distribution of these diseases is scarce in the country. SUS Hospital Information Systems only provide hospitalization or mortality data, that is, they are limited only to the most severe cases of diarrheal diseases that lead to death or hospital admissions and do not allow us to distinguish whether different hospitalizations are from the same patient or different patients. New cases and less serious cases are not properly recorded and made available. Thus, there may be biases in the data that may lead to underestimating cases and diverting the focus from the problem and measures aimed at its prevention, such as improving basic sanitation, for example⁶²62 Barreto ML, Genser B, Strina A, Teixeira MG, Assis AMO, Rego RF, Teles CA, Prado MS, Matos SMA, Santos DN, Santos LA, Cairncross S. Effect of city-wide sanitation programme on reduction in rate of childhood diarrhoea in northeast Brazil: assessment by two cohort studies. Lancet 2007; 370(9599):1622-1628.. This lack of information was one of the main limitations of this study.

Other limitations include the use of secondary health data, which rely on records and may not reproduce reality very accurately. Likewise, the number of meteorological stations and data quality in the Amazon region of the country are very limited²⁸28 Fonseca PAM, Hacon SS, Reis VL, Costa D, Brown IF. Using satellite data to study the relationship between rainfall and diarrheal diseases in a Southwestern Amazon basin. Cien Saude Colet 2016; 21(3):731-742.. The results of this study, when considering monthly hospitalization data for the general population of the entire municipality of Rio Branco, without considering major characteristics of this population, such as socioeconomic factors, for example, and their geographic delimitations does not allow us to characterize the population groups most vulnerable to infectious diarrheal diseases.

However, this study provided information on how and how much climate can influence the distribution of these diseases in this region and allowed the identification of factors that warrant further investigation. Expanded knowledge on the relationship between climate and health at the regional level is fundamental for the implementation of precautionary, prevention and impact-mitigating actions, especially for the most exposed population¹1 Barreto ML, Teixeira MG, Bastos FI, Ximenes RAA, Barata RB, Rodrigues LC. Successes and failures in the control of infectious diseases in Brazil: social and environmental context, policies, interventions, and research needs. Lancet 2011; 377(9780):1877-1889.^,1515 World Health Organization (WHO). Atlas of Heath and Climate. 2012. [acessado 2013 Nov 2]. Disponível em: http://www.who.int/globalchange/publications/atlas/report/en/
http://www.who.int/globalchange/publicat... . A next step would be to study the socio-environmental vulnerability areas in association with socioeconomic factors in the municipality so that the different local realities are identified.

Conclusion

Even with the sharp decline of deaths and hospitalizations due to infectious diarrheal diseases in the last decades, these are still a serious public health problem in Brazil, together with other infectious diseases, mainly because Brazil is undergoing a rapid and poor urbanization process. The Brazilian Amazon region has a typical and favorable setting for the permanence, expansion and distribution of these diseases. Advances occurred in relation to the coverage of water supply and sanitary sewage in the country. However, there are still inequalities related to these services, which shows the importance of diarrheal diseases in the Brazilian epidemiological setting⁸8 Oliveira AF, Leite IC, Valente JG. Carga Global das doenças diarreicas atribuíveis ao sistema de abastecimento de água e saneamento em Minas Gerais, Brasil, 2005. Cien Saude Colet 2015; 20(4):1027-1036.. In addition, since it mainly involves the poorest people, this disease draws much less attention than most other diseases¹1 Barreto ML, Teixeira MG, Bastos FI, Ximenes RAA, Barata RB, Rodrigues LC. Successes and failures in the control of infectious diseases in Brazil: social and environmental context, policies, interventions, and research needs. Lancet 2011; 377(9780):1877-1889.^,22 Bühler HF, Ignotti E, Neves SMAS, Hacon SS. Análise espacial de indicadores integrados determinantes da mortalidade por diarreia aguda em crianças menores de 1 ano em regiões geográficas. Cien Saude Colet 2014; 19(10):4131-4140..

Thus, this study focuses on the impact of these diseases in this population and provides a model where the river’s level can be used as a trend predicting indicator of infectious diarrheal diseases events with potential to generate hospitalizations. This type of study is instrumental to increased knowledge about how the region’s climate can change and interfere with the occurrence of these diseases, especially considering the Amazon region as being at great risk of extreme climatic events, vulnerable to the occurrence of floods and where the rates of morbimortality from infectious diarrheal diseases are still quite high.

Acknowledgments

We wish to thank the Coordination of Improvement of Higher Education Personnel and to the State Health Secretariat of Acre for the funding of the Interinstitutional Doctorate of the Faculty of Public Health of USP and the Federal University of Acre, as well as the Foundation for Research Support of the State of São Paulo, and the National Council for Scientific and Technological Development, for the support to productivity in research.

References

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History