ABSTRACT

OBJECTIVE

To investigate the association between bacterial vaginosis and cervical human papillomavirus (HPV) infection in young and adult women.

METHODS

This systematic review and meta-analysis was based on the Prisma methodological guidelines. PubMed and Web of Science were searched using the following descriptors: “bacterial vaginosis and HPV”, in June 2019. Articles published from 2012 to 2019 were included. Inclusion criteria were original studies that investigated the association between bacterial vaginosis and cervical HPV infection; articles published in English, Spanish or Portuguese; studies conducted in young and adult, non-pregnant, non-HIV-infected women; studies that used the Nugent criteria for the diagnosis of bacterial vaginosis and studies in which the detection of HPV used the polymerase chain reaction technique. Assembled data, odds ratio (OR) and respective 95% confidence intervals (95%CI) were estimated for the association between bacterial vaginosis and cervical HPV infection using random-effects models. A bilateral value of p < 0.05 was considered statistically significant.

RESULT

Six studies were selected for analysis and demonstrated association between bacterial vaginosis and cervical HPV infection (OR = 2.68; 95%CI: 1.64–4.40; p < 0.001).

CONCLUSION

Bacterial vaginosis was considered a risk factor for cervical HPV infection, since women with bacterial vaginosis were more likely to be infected with HPV.

Bacterial Vaginosis; Epidemiology; Papillomavirus Infections; Risk factors; Revision

INTRODUCTION

Bacterial vaginosis has been reported as a cofactor for the HPV infection¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... , being the most common cause of vaginal discharge and affecting about 30% of women worldwide⁴4. Bautista CT, Wurapa E, Sateren WB, Morris S, Hollingsworth B, Sanchez JL. Bacterial vaginosis: a synthesis of the literature on etiology, prevalence, risk factors, and relationship with chlamydia and gonorrhea infections. Mil Med Res. 2016;3:4. https://doi.org/10.1186/s40779-016-0074-5
https://doi.org/10.1186/s40779-016-0074-... ,⁵5. Bagnall P, Rizzolo D. Bacterial vaginosis: a practical review. JAAPA. 2017;30(12):15-21. https://doi.org/10.1097/01.JAA.0000526770.60197.fa
https://doi.org/10.1097/01.JAA.000052677... . The bacterial infection results from a change in the vaginal microbiota with a decrease in Lactobacillus spp., commonly present in the vaginal environment, with polymicrobial etiology and predominance of anaerobic microorganisms⁶6. Reid G. Is bacterial vaginosis a disease? Appl Microbiol Biotechnol. 2018;102(2):553-8. https://doi.org/10.1007/s00253-017-8659-9
https://doi.org/10.1007/s00253-017-8659-... ,⁷7. Paavonen J, Brunham RC. Bacterial vaginosis and desquamative inflammatory vaginitis. N Engl J Med. 2018;379:2246-54. https://doi.org/10.1056/NEJMra1808418
https://doi.org/10.1056/NEJMra1808418... .

HPV infection and bacterial vaginosis have common risk factors, including: early onset of sexual activity, history of multiple partners, history of other sexually transmitted infection (STI), and inconsistent condom use⁴4. Bautista CT, Wurapa E, Sateren WB, Morris S, Hollingsworth B, Sanchez JL. Bacterial vaginosis: a synthesis of the literature on etiology, prevalence, risk factors, and relationship with chlamydia and gonorrhea infections. Mil Med Res. 2016;3:4. https://doi.org/10.1186/s40779-016-0074-5
https://doi.org/10.1186/s40779-016-0074-... ,⁸8. Chelimo C, Wouldes TA, Cameron LD, Elwood JM. Risk factors for and prevention of human papillomaviruses (HPV), genital warts and cervical cancer. J Infect. 2013;66(3):207-17. https://doi.org/10.1016/j.jinf.2012.10.024
https://doi.org/10.1016/j.jinf.2012.10.0... ,⁹9. Ribeiro AA, Costa MC, Alves RRF, Villa LN, Saddi VA, Carneiro MAS, et al. HPV infection and cervical neoplasia: associated risk factors. Infect Agent Cancer. 2015;10:16. https://doi.org/10.1186/s13027-015-0011-3
https://doi.org/10.1186/s13027-015-0011-... , leading to the hypothesis that both are associated¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... .

Studies have shown a greater diversity of vaginal bacteria in HPV positive women than in HPV negative women¹⁰10. Di Paola M, Sani C, Clemente AM, Iossa A, Perissi E, Castronovo G, et al. Characterization of cervico-vaginal microbiota in women developing persistent high-risk Human Papillomavirus infection. Sci Rep. 2017;7:10200. https://doi.org/10.1038/s41598-017-09842-6
https://doi.org/10.1038/s41598-017-09842... ,¹¹11. Champer M, Wong AM, Champer J, Brito IL, Messer PW, Hou JY, et al. The role of the vaginal microbiome in gynaecological cancer. BJOG. 2018;125(3):309-15. https://doi.org/10.1111/1471-0528.14631
https://doi.org/10.1111/1471-0528.14631... . The vaginal microbiota plays an important role in women’s reproductive health and serves as the first line of defense against STI¹²12. Nasioudis D, Linhares IM, Ledger WJ, Witkin SS. Bacterial vaginosis: a critical analysis of current knowledge. BJOG. 2017;124(1):61-9. https://doi.org/10.1111/1471-0528.14209
https://doi.org/10.1111/1471-0528.14209... . It also seems to have a crucial role in the prevention of HPV infection, since it accelerates the clearance of the virus, so an imbalance of vaginal microbiota could be a synergistic factor for the development of HPV related diseases¹²12. Nasioudis D, Linhares IM, Ledger WJ, Witkin SS. Bacterial vaginosis: a critical analysis of current knowledge. BJOG. 2017;124(1):61-9. https://doi.org/10.1111/1471-0528.14209
https://doi.org/10.1111/1471-0528.14209... .

Three meta-analyzes investigated the association between bacterial vaginosis and HPV infection in recent years¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... . Although the results obtained in those studies are important, they included heterogeneous populations and diverse methods for both HPV detection and bacterial vaginosis diagnostic, making it difficult to compare and to interpret the results. In the present systematic review and meta-analysis, we only included declared HIV-negative, young and adult, non-pregnant women. However, all the selected studies used PCR as the chosen method for HPV DNA detection and the Nugent criteria for the diagnosis of bacterial vaginosis, allowing a lower risk of bias in the interpretation of results. Therefore, the purpose of this systematic review and meta-analysis was to investigate the association between bacterial vaginosis and cervical HPV infection in young and adult women.

METHODS

This systematic review and meta-analysis used the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes: The Prisma Statement (Prisma)¹⁵15. Page JM, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021;372:n71. https://doi.org/10.1136/bmj.n71
https://doi.org/10.1136/bmj.n71... as foundation. Established using an acronym for patient, intervention, comparison, and “outcome” - PICO¹⁶16. Santos CMC, Pimenta CAM, Nobre MRC. A estratégia PICO para a construção da pergunta de pesquisa e busca de evidências. Rev Latino-Am Enfermagem. 2007;15(3):1-4.- the guiding question of the study was: is there an association between bacterial vaginosis and cervical HPV infection in young and adult women? “Patients” were young and adult women with the presence or absence of bacterial vaginosis, and “outcome” indicates the presence or absence of cervical HPV infection.

The databases National Library of Medicine (PubMed/Medline) and Science Citation Index Expanded (Web of Science) were searched using descriptors included in the Medical Subject Headings (MeSH terms): “bacterial vaginosis and HPV”. The search for the studies was carried out in June 2019.

Inclusion criteria: original studies that investigated the association between bacterial vaginosis and cervical HPV infection, articles published in English, Spanish or Portuguese, studies conducted in young and adult women, over 15 years old, non-pregnant, declared HIV-negative, studies that used the Nugent criteria¹⁷17. Nugent RP, Krohn MA, Hillier SL. Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation. J Clin Microbiol. 1991;29(2):297-301. https://doi.org/10.1128/jcm.29.2.297-301.1991
https://doi.org/10.1128/jcm.29.2.297-301... for the diagnosis of bacterial vaginosis, and studies in which HPV detection has been carried out using the polymerase chain reaction (PCR) technique. Exclusion criteria: studies of systematic reviews, meta-analyzes and case reports. The articles were included regardless of the publication period. All studies were read and analyzed by two independent researchers (BCTM, VAS). Pregnant and HIV-positive women were excluded from this study because these conditions can function as cofactors for bacterial vaginosis and HPV infection, respectively. We only included young and adult women in order to avoid further confounding factors. The diagnostic methods for bacterial vaginosis and HPV established in this study are considered the gold standard for detecting these conditions¹⁷17. Nugent RP, Krohn MA, Hillier SL. Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation. J Clin Microbiol. 1991;29(2):297-301. https://doi.org/10.1128/jcm.29.2.297-301.1991
https://doi.org/10.1128/jcm.29.2.297-301... .

This systematic review was registered in the International Prospective Register of Systematic Reviews (Prospero) under protocol number: CRD42020140790.

Initially, the titles and abstracts were read from each database. Then, the studies pre-selected in the previous step were read in full. From the selected studies, the following information was extracted: authors and year of publication, number of participants in the research, type of study, country of study, mean age, method of diagnosis of bacterial vaginosis and HPV, positivity for bacterial vaginosis and HPV infection in each group.

In order to identify potential risks of bias, studies were assessed based on criteria adopted by Brusselaers et al.²2. Brusselaers N, Shrestha S, Wijgert J, Verstraelen H. Vaginal dysbiosis and the risk of human papillomavirus and cervical cancer: systematic review and meta-analysis. Am J Obstet Gynecol. 2019;221(1):9-18.e8. https://doi.org/10.1016/j.ajog.2018.12.011
https://doi.org/10.1016/j.ajog.2018.12.0... (2019), presented in Chart 1. Two researchers performed the search and reading of the articles and the data collection instrument was completed independently (Chart 1). We subsequently compared the data in order to minimize possible risks of measurement bias (error in interpretation of results and design). After the application of the classification and assessment tool for the quality of the articles (Chart 2), a score of up to 8 points was assigned to each study. No divergence regarding the evaluation of publications was reported.

This meta-analysis with the objective of verifying the association between bacterial vaginosis and HPV infection was conducted in the Stata program, version 15.0. Initially, the study estimated the prevalence of HPV in both groups (with and without bacterial vaginosis). Assuming that I² values of 25, 50, and ≥ 75% represent low, medium and high heterogeneity, respectively, we used this statistic to verify the heterogeneity between the studies. For combined estimation of study data, odds ratio (OR) and respective 95%CI were calculated for the association between bacterial vaginosis and cervical HPV infection, using random effects models and the results were presented in forest plot. A bilateral p < 0.05 value was considered statistically significant.

RESULTS

Six articles published in English from 2012 to 2019 were included in the study, as described in Figure 1. Table 1 summarizes the results. This meta-analysis assessed a total of 7.119 women (1.131 cases and 5.988 controls). In each study the number of them ranged from 181 to 3.502 and their average age ranged from 16 to 38.5 years. Only one study had a cohort design²⁰20. Oakeshott P, Aghaizu A, Reid F, Howell-Jones R, Hay PE, Sadiq ST, et al. Frequency and risk factors for prevalent, incident, and persistent genital carcinogenic human papilloma virus infection in sexually active women: community based cohort study. BMJ. 2012;344:e4168. https://doi.org/10.1136/bmj.e4168
https://doi.org/10.1136/bmj.e4168... , and the others were cross-sectional studies. From the included studies, only two evaluated the association between bacterial vaginosis and CIN²¹21. Caixeta CAC, Ribeiro AA, Segatti KD, Saddi VA, Alves RRF, Carneiro MAS, et al. Association between the human papillomavirus, bacterial vaginosis and cervicitis and the detection of abnormalities in cervical smears from teenage girls and young women. Diagn Cytopathol. 2015;43(10):780-5. https://doi.org/10.1002/dc.23301
https://doi.org/10.1002/dc.23301... ,²²22. Lu H, Jiang PC, Zhang XD, Hou WJ, Wei ZH, Lu JQ, et al. Characteristics of bacterial vaginosis infection in cervical lesions with high-risk human papillomavirus infection. Int J Clin Exp Med. 2015;8(11):21080-8.. Asia (33.3%) and America (33.3%) conducted most of them with two studies in each continent, then one in Europe (16.7%), and one in South Africa (16.7%), as shown in Table 1.

After applying the classification tool and evaluating the quality of the articles, we classified all studies as low risk of bias, with scores between 6 and 8, therefore, presenting high quality evidence.

Figure 2 shows the association between bacterial vaginosis and HPV infection through a random effect meta-analysis. The pooled estimate showed a significant association between bacterial vaginosis and cervical HPV infection (OR = 2.68; 95%CI: 1.64–4.40; p < 0.001). Therefore, women with bacterial vaginosis were 2.68 times more likely to have cervical HPV infection when compared with women without bacterial vaginosis. Evidence of heterogeneity was found between studies (I²: 87.8%; p < 0.001).

DISCUSSION

The present systematic review and meta-analysis investigated the relationship between bacterial vaginosis and cervical HPV infection, demonstrating a significant association between these conditions. When compared with women without bacterial vaginosis, the random effect model showed that women with bacterial vaginosis were 2.68 times more likely to have cervical HPV infection. The outstanding of our systematic review and meta-analysis is the inclusion criteria of the selected studies comprising those that investigated only declared HIV-negative, young and adult, non-pregnant women. All the selected studies used PCR as the chosen method for HPV DNA detection and the Nugent criteria for the diagnosis of bacterial vaginosis. Furthermore, this study followed PRISMA recommendations in this review, and obtained Prospero registration and certification.

Performing a sensitive and specific exponential amplification of a fragment of the virus genome¹⁸18. Abreu ALP, Souza RP, Gimenes F, Consolaro MEL. A review of methods for detect human Papillomavirus infection. Virol J. 2012;9:262. https://doi.org/10.1186/1743-422X-9-262
https://doi.org/10.1186/1743-422X-9-262... ,¹⁹19. Zeferino LC, Bastos JB, Vale DBAP, Zanine RM, Melo YLMF, Primo WQSP, et al. Guidelines for HPV-DNA testing for cervical cancer screening in Brazil. Rev Bras Ginecol Obstet. 2018;40(6):360-8. https://doi.org/10.1055/s-0038-1657754
https://doi.org/10.1055/s-0038-1657754... , the PCR method uses enzymatic synthesis of viral DNA. Nevertheless, the Nugent criterion consists of counting bacterial morphotypes in a smear stained by the Gram method, quantified and classified using a score, mainly based on the presence or absence of Lactobacillus spp.¹⁷17. Nugent RP, Krohn MA, Hillier SL. Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation. J Clin Microbiol. 1991;29(2):297-301. https://doi.org/10.1128/jcm.29.2.297-301.1991
https://doi.org/10.1128/jcm.29.2.297-301... .These methods were used as the inclusion criteria because they allow more accurate diagnosis, with greater sensitivity and specificity¹⁷17. Nugent RP, Krohn MA, Hillier SL. Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation. J Clin Microbiol. 1991;29(2):297-301. https://doi.org/10.1128/jcm.29.2.297-301.1991
https://doi.org/10.1128/jcm.29.2.297-301... .

Bacterial vaginosis appears to be associated with an increased risk of cervical HPV infection and the inverse relationship (cervical HPV infection associated with an increased risk of bacterial vaginosis) also appears to be consistent¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... . Three systematic reviews with meta-analyses developed in recent years showed a significant association between bacterial vaginosis and cervical HPV infection, since the chance of women with bacterial vaginosis acquiring a cervical HPV infection in these studies ranged from 1.33 to 2.62¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... . However, these studies are heterogeneous, as they compare different patient profiles with positive results for other STIs, different methods of detection of HPV and diagnosis of bacterial vaginosis¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... , which makes consistent conclusions difficult.

HPV has several evasion mechanisms from the immune system, which can favor changes in the vaginal epithelium, causing imbalance in the local microbiota, degradation and alteration of the cervical mucus and the appearance of bacterial vaginosis²2. Brusselaers N, Shrestha S, Wijgert J, Verstraelen H. Vaginal dysbiosis and the risk of human papillomavirus and cervical cancer: systematic review and meta-analysis. Am J Obstet Gynecol. 2019;221(1):9-18.e8. https://doi.org/10.1016/j.ajog.2018.12.011
https://doi.org/10.1016/j.ajog.2018.12.0... ,²⁶26. Brotman RM, Shardell MD, Gajer P, Tracy JK, Zenilman JM, Ravel J, et al. Interplay between the temporal dynamics of the vaginal microbiota and human papillomavirus detection. J Infect Dis. 2014;210(11):1723-33. https://doi.org/10.1093/infdis/jiu330
https://doi.org/10.1093/infdis/jiu330... . The mechanism by which bacterial vaginosis can influence the acquisition of cervical infection by HPV remains unknown, however, there are some hypotheses including the presence of inflammatory cytokines in the vaginal environment due to a decrease in Lactobacillus spp., and the proliferation of microorganisms as a result of changes in the vaginal microbiota²⁷27. Gillet E, Meys JFA, Verstraelen H, Verhelst R, De Sutter P, Temmerman M, et al. Association between bacterial vaginosis and cervical intraepithelial neoplasia: systematic review and meta-analysis. PLoS One. 2012;7(10):e45201. https://doi.org/10.1371/journal.pone.0045201
https://doi.org/10.1371/journal.pone.004... . The degradation of mucin as a consequence of the increased production of some enzymes – especially sialidase – is responsible for breaking down cervical mucus components, leading to bullous discharge that covers the vagina and further favors the degradation of the lining layer of the cervical epithelium, which may cause microlesions and changes in epithelial cells¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... ,³⁰30. Briselden AM, Moncla BJ, Stevens CE, Hillier SL. Sialidases (neuraminidases) in bacterial vaginosis and bacterial vaginosis-associated microflora. J Clin Microbiol. 1992;30(3):663-6. https://doi.org/10.1128/jcm.30.3.663-666.1992
https://doi.org/10.1128/jcm.30.3.663-666... . Such enzymes can promote virulence through the destruction of the mucosal protective barrier and, therefore, increase the susceptibility to cervical infection by HPV, facilitating the adhesion, invasion and, eventually, incorporation of HPV oncogenes in the genome of cells in the transformation zone cervical¹1. Gillet E, Meys JFA, Verstraelen H, Bosire C, De Sutter P, Temmerman M, et al. Bacterial vaginosis is associated with uterine cervical human papillomavirus infection: a meta-analysis. BMC Infect Dis. 2011;11:10. https://doi.org/10.1186/1471-2334-11-10
https://doi.org/10.1186/1471-2334-11-10... ,³⁰30. Briselden AM, Moncla BJ, Stevens CE, Hillier SL. Sialidases (neuraminidases) in bacterial vaginosis and bacterial vaginosis-associated microflora. J Clin Microbiol. 1992;30(3):663-6. https://doi.org/10.1128/jcm.30.3.663-666.1992
https://doi.org/10.1128/jcm.30.3.663-666... .

Furthermore, other effects include changes in the cervical mucosal barrier³⁰30. Briselden AM, Moncla BJ, Stevens CE, Hillier SL. Sialidases (neuraminidases) in bacterial vaginosis and bacterial vaginosis-associated microflora. J Clin Microbiol. 1992;30(3):663-6. https://doi.org/10.1128/jcm.30.3.663-666.1992
https://doi.org/10.1128/jcm.30.3.663-666... and release of volatile amines, which also increases levels of oxidative stress³¹31. Georgescu SR, Mitran CI, Mitran MI, Curuntu CI, Sarbu MI, Matei C, et al. New insights in the pathogenesis of HPV infection and the associated carcinogenic processes: the role of chronic inflammation and oxidative stress. J Immunol Res. 2018;2018:5315816. https://doi.org/10.1155/2018/5315816
https://doi.org/10.1155/2018/5315816... . Another hypothesis is that the anaerobic bacterial metabolism observed in bacterial vaginosis produces ammonia and ammonium nitrite in vaginal secretions, both with carcinogenic potential, can cause changes in cervical epithelial cells, such as exfoliation and transformation³3. Liang Y, Chen M, Qin L, Wan B, Wang H. A meta-analysis of the relationship between vaginal microecology, human papillomavirus infection and cervical intraepithelial neoplasia. Infect Agent Cancer. 2019;14:29. https://doi.org/10.1186/s13027-019-0243-8
https://doi.org/10.1186/s13027-019-0243-... .

A significant association was described between bacterial vaginosis and cervical HPV infection in the present systematic review and meta-analysis. These findings reinforce the need for healthcare professionals to carefully investigate the presence of bacterial vaginosis in young and adult women in association with cervical HPV infection and related injuries.

The main limitation of this study is the fact that it included only studies published and available in the two consulted databases, which may have caused publication bias, due to the tendency to selectively publish statistically significant results. In addition, the lack of some data in the literature can also lead to a bias in the results.

One of the main complaints of women who visit the gynecologist is the presence of vaginal discharge, however, for many times an accurate diagnosis of this symptom is not achieved, resulting in an increase in periodic consultations. Bacterial vaginosis can appear as a recurrent condition, implying in a careful view of this condition by the medical professional. We believe that diagnosis and effective treatment of women with this condition can contribute to reduce cervical HPV infection. Bacterial vaginosis was considered a risk factor for cervical HPV infection, since women with bacterial vaginosis were more likely to be infected with it.

REFERENCES

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