MEM INST OSWALDO CRUZ, RIO DE JANEIRO, 104(6) September 2009
PAGES: 885-891 DOI: 10.1590/S0074-02762009000600011 Full paper
Risk factors associated with human papillomavirus infection in two populations from Rio de Janeiro, Brazil

Katia C SilvaI; Maria Luiza Garcia RosaII; Natalia MoysesI; Larissa A AfonsoI; Ledy HS OliveiraI; Silvia MB CavalcantiI, +

IDepartamento de Microbiologia e Parasitologia, Instituto Biomédico, Universidade Federal Fluminense, R. Prof. Ernani Melo 101, sala 321, 24210-130 Niterói, RJ, Brasil
IIDepartamento de Epidemiologia e Bioestatística, Hospital Universitário Antônio Pedro

Abstract

We investigated human papillomavirus (HPV) infection in two female populations from diverse socio-economic strata from the state of Rio de Janeiro and we also investigated the possible co-factors related to infection and the progression to cancer. In Group I, the reference group of this study, 10.7% of the patients presented HPV infection, as detected by generic PCR, while in Group II (low socio-demographic conditions) HPV was detected in 31.1% of the samples. HPV16 was the most prevalent virus type found in both Groups I and II (5.3% and 10%, respectively), followed by HPV 18 (1.3% and 4.7%, respectively). Although only a small sample was analysed, we detected differences among the groups regarding the rates of HPV infection, HPV types, age, ethnicity, familial income, schooling, marital status, parity, tobacco smoking and oral contraceptive use. For Group I, the Papanicolaou test was the most powerful independent factor associated with HPV status, followed by an age of under 30 years old, the number of sexual partners and black ethnicity. Our data are in agreement with the co-factors that are typically described for the developed world. For Group II, the Pap test was also the most relevant variable that was analysed, but the history of other sexually transmitted diseases and the use of alcohol were additional factors that were implicated in infection. These findings point out the need for the development of general and specific strategies for HPV screening of all Brazilian women.

The World Health Organization presents data placing cervical cancer as the second most prevalent malignant neoplasia in women worldwide, with nearly 500,000 new cases and 250,000 deaths each year (Baseman & Koutsky 2005). Most of the cases arise in the developing world, where organised screening programmes using the Papanicolaou preventive test have not been successfully implemented (Jones 1999). In Brazil, cervical cancer is the second most prevalent cause of death from cancer (INCA 2008). In the last two decades, malignant transformation has progressively been detected in younger women (Pereira et al. 2007).

Large epidemiological and prospective studies conducted in various countries have shown that the risk of developing cervical cancer is strongly associated with the presence and persistence of high-risk genital papillomavirus types (Bosh & San José 2003). Nevertheless, it has been established that human papillomavirus (HPV) infection is the most important, but not the exclusive, risk factor to cervical cancer. Hence, epidemiological investigations have focused on the role of co-factors associated with cancer progression (Baseman & Koutsky 2005).

Brazil is a large country, representing diverse socio-economical conditions in different regions and states. Cancer incidences also vary extensively, ranging from 26.7/105 in the South to 43.8/105 in the North (INCA 2008). Even within the Rio de Janeiro metropolitan area, we can find a portion of the population in a high urban development index and another portion of the population living under the poverty line.

The literature has already indicated that social and economic differences determine diverse profiles in cancer outcome. Additionally, important co-factors are related to cancer, such as sexual behaviour, the number of years of schooling and familial income, among others. However, little is known about these co-factors in relation to the risk of HPV infection (Cuschieri et al. 2004). It is also important to note that most of the previously published Brazilian research has focused on women patients who attended public health clinics and that this group presented high HPV frequencies (Cavalcanti et al. 2000, Oliveira et al. 2007, Pereira et al. 2007). Little is known about middle class female groups, but lower levels of HPV infection might be expected (Syrjanen et al. 2003, Naud et al. 2006). The aim of our study was to evaluate HPV frequency and to determine if socio-economic differences are related to the frequency of HPV infections in two different populations. Finally, we aimed to verify whether or not the cancer co-factors are present in different degrees. Thus, we investigated two populations of females, who attended either a private or a public gynaecological service, from the state Rio de Janeiro. Prophylactic vaccines for HPV infection are now a reality, but since geographical variations in the prevalence of HPV types and co-factors have been documented worldwide (Lepique et al. 2009), further knowledge of the epidemiological data regarding HPV infection in our country may assist health authorities in planning local prophylactic and therapeutic strategies of cancer control.

 

PATIENTS, MATERIALS AND METHODS

Study design - This was a cross-sectional study conducted in order to verify HPV infection rates in two female populations. The sample size was determined according to the female population from Maricá and Itaboraí (approx. 70,000 adult women). The expected HPV prevalence for Group I and Group II ranged from 10-25%, respectively. We also evaluated the co-factors related to the risk of HPV infection and to cancer outcome. The study population included 150 women who attended a private gynaecological clinic from the Município de Maricá (Group I - reference group, minor risk) and 150 women who attended the Policlínica Francisco da Cruz Nunes, Município de Itaboraí (Group II - major risk), from January-December 2005. The women were subjected to a routine exam and were randomly selected for the study. The cervical smears were collected with a cervical cytobrush and were transported in Tris-EDTA buffer and stored at -20ºC.

Questionnaire - A self-administered questionnaire about the demographic data and medical history was answered by all of the women enrolled in this study, following informed consent. All of the women were then interviewed with respect to their reproductive and sexual life variables. The women with a recent history of treatment of lesions associated with HPV, conisation or hysterectomy were excluded. The medical services from the Universidade Federal Fluminense adopted a standard questionnaire that was then applied in this study. The study protocol was approved by the Ethical Committee of the Universidade Federal Fluminense.

Cytologic test - The Papanicolaou-tested smears were classified as normal for a normal epithelium, inflammatory for minor alterations of cells, low grade squamous intraepithelial lesions (LSIL) for low grade neoplasia, high grade squamous intraepithelial lesions (HSIL) for moderate/severe neoplasia, invasive cancer and ASCUS for atypical squamous cells of undetermined significance.

DNA extraction - The samples were incubated for 4 h at 50ºC in digestion buffer (10 mM TRIS-HCl pH 8.3, 1 mM EDTA pH 8.0, 0.5% Tween-20, 400 ?g/mL proteinase K). DNA was extracted with phenol-chloroform-isoamyl alcohol, precipitated with 0.3 M sodium acetate and three volumes of 100% ice cold ethanol, washed with 70% ethanol, air dried and resuspended in 50 ?L of sterile water.

HPV detection by the polymerase chain reaction (PCR) - Consensus primers, MY09/11, which amplify 450 bp DNA sequences within the L1 region of HPV, were used to detect generic HPV DNA. The amplification was carried out in a 50 ?L reaction mixture (1X PCR buffer, 200 ?M dNTPs, 1.5 mM MgCl2, 50 pmol of each primer, 0.25 U unit of Taq polymerase and 5 ?L of sample) as described elsewhere (Pereira et al. 2007). The ?-actin primers were used as an internal control. PCR products were analysed on a 1.3% agarose gel with ethidium bromide staining for visualisation of DNA under an ultraviolet light.

HPV typing - HPV typing was done by PCR amplification with primers from the E6 gene DNA sequences of HPV 6, 11,16, 18, 31, 33, 35 and 58 (Pereira et al. 2007).

Statistical analysis - A data bank including the demographic and behavioural factors was generated and analysed using the EPInfo 2004 statistical software package (Center for Disease Control and Prevention, Atlanta, EUA, 2004). The biological, socio-economic and demographic differences were compared through Chi-square tests with a Yates correction. The significance level of tests (p) was set at 0.05. The association between exposure and outcome was expressed by means of prevalence ratios (PR) (Coutinho et al. 2008).

 

RESULTS

The groups that were analysed were composed of population cohorts attended at their annual preventive cytological test.

The average age of participants was 33 years, ranging from 14-79 years old. The profiles of the demographic and socio-economic characteristics of the two studied groups are presented in Table I. Analysis revealed that there were statistically significant differences regarding mean age of the female population, ethnicity, familial income, schooling, marital status, menarche, parity, tobacco smoking and use of oral contraceptive (OC use).

Regarding HPV infection, we found that in Group I, HPV DNA was detected in 10.7% of the patients (16/150) while in Group II, the HPV DNA was detected in 31.1% (46/150) of the patients. HPV 16 was the most prevalent type found in both groups (5.3% and 10%, respectively), followed by HPV 18 (1.3% and 4.7%, respectively). The high-risk types, 33 and 58, were both found at 0.7% in Group I and at 4% and 2%, respectively, in Group II. Types 6, 11 and 35 were only found in Group II (2%, 0.7% and 2%, respectively) and HPV 31 was not detected. Multiple infections were found in 0.7% of the samples from Group I and in 3.3% of the samples from Group II. Both of the groups presented MY positive samples (4 samples in Group I and 12 samples in Group II) that remained untyped by PCR specific primers (Table II).

As presented in Table II, the patients from Group II had a 1.72-fold greater chance of being infected by HPV (p < 0.001). This group also had a 2.1-fold greater chance of being infected by the high-risk viruses. The cytological test results showed that Group I had a low rate of HSIL (1.3%) while Group II had an 8.7% rate of HSIL. The statistical analysis demonstrated that there was a 1.77-fold greater chance of a woman presenting HSIL if she belonged to Group II (p < 0.001), when compared to women from Group I.

The bivariate-analysis showed that there were specific variables associated with HPV infection in these distinct populations (Table III): in Group I, women younger than 30 years old had a 3.1-fold greater chance of being infected by HPV, as well as black women (PR = 5.2), single, separated or widowed women (PR = 2.7), women with more than one sexual partner (PR = 8.4) and women using oral contraceptives (PR = 2.3). Patients who presented altered results upon cytological testing had a 27.7-fold greater chance of being infected with HPV, compared to women without cytological alterations (p < 0.001). Following analysis of Group II, we observed there to be diverse co-factors related to HPV infection: women using alcohol had a 2.5-fold greater chance of being infected (p = 0.001) and tobacco smoking was related to increased risk of infection (PR = 2.0) as well as a history of other sexually transmitted diseases (STD) (PR = 2.7). Early beginning of sexual life gave borderline results (PR = 1.5). The patients presenting altered results upon cytological testing had a 4.3-fold greater chance of being infected with HPV compared to women without cytological alterations (p < 0.001).

 

DISCUSSION

In Brazil, cervical cancer remains a major public health problem and it has a marked variation in incidence between the different regions of this vast country. An organised national screening programme exists, but in practice it performs inadequately, except for some local programmes (Oliveira et al. 2007). Our study aimed to verify if women in these different regions are differently exposed to the known risk factors of the disease. As expected, the population variables revealed that the two groups were statistically different regarding the rates of HPV infection, frequency of high grade lesions, age, ethnicity, familial income, schooling, marital status, menarca, parity, tobacco smoking and OC uses (Table I).

With regard to HPV infection, we detected a strongly different prevalence amongst the groups: 10.7% of Group I presented HPV infection, while in Group II, nearly 31.1% presented HPV infection (Table II) (p < 0.001). Naud et al. (2006) found infection prevalence rates of 31.4%, similar to those found for Group II (31.1%), after studying a similar population, but with a lower mean age (26.6 years old). It is noticeable that estimates of HPV prevalence among women around the world range from 2-44% (Cushieri et al. 2004, Clifford et al. 2005). Such a wide variation is explained by differences in the age range of the studied groups as well as the sensitivity of the DNA assay for detection of HPV infection (Bosh & San Jose 2003). Due to our small sample size, the stratification by age significantly compromised the statistical power of the analysis, thus requiring further studies that use an adequate number of samples.

The literature has already documented that cervical cancer is a disease associated with populations that subside in lower developed areas that are associated with poverty and its particular socio-demographic variables (Jones 1999). However, HPV infection, now regarded as an endpoint marker for cervical cancer, is related to socio-demographic factors. The rate of prevalence of HPV infection in reference Group I is considered to be low and this is similar to studies from developed countries, such as Italy, the Netherlands and Spain (Clifford et al. 2005). Thus, this reinforces the idea that higher socio-demographic variables result in better control over not only cervical cancer but also HPV infection and likely other STDs.

Following analysis of the profile of HPV types, we noticed that HPV 16 was the most prevalent type found in both Group I and Group II (5.3% and 10%, respectively), followed by HPV 18 (1.3% and 4.7%, respectively). Giuliano et al. (2002) and Syrjanen et al. (2003) described similar results following studies of random populations in Russia and the USA. In Brazil, a large cohort study in São Paulo presented similar results for HPV16, but the prevalence of HPV18 was lower (Villa et al. 2000).

In this study, we investigated the cytological status of the two groups. In both groups, 86% of the patients presented with a normal Papanicolaou test (Pap test) result or an inflammatory result. However, it is interesting to note that the other 14% of the results were statistically different: Group II presented 13 high-risk lesions among the 20 altered Pap tests, while Group I presented only two high-grade lesions, among the 20 positive Papanicolaou smears, revealing a significant risk of cancer development in Group II (p < 0.0001) (Table II).

Despite these differences, the most meaningful result was that an altered cytological result for the two studied populations could then be evaluated as a predictor of HPV infection. In Group I, patients who presented altered results upon cytological testing had a 27.7-fold greater chance of being infected with HPV when compared to women without cytological alterations (p < 0.001) and Group II patients had a 4.3-fold greater chance of being infected with HPV (p < 0.001). In fact, this was expected since the Pap test is a powerful method of clinical detection of active infections caused by HPV in the genital tract. Franco et al. (1999), as well as Naud et al. (2006), also described the Pap test as the most important predictor of HPV infection. In fact, the Pap test may be the only meaningful factor related to risk, since the Pap test can be regarded as an indication that the woman had access to medical care services. Therefore, as expected, these results corroborate the use of the Pap test as an outstanding exam for screening women at risk of HPV infection. The importance of cytology as a marker for cervical cancer has led many authors to reemphasise the relevance of an altered Pap test as an indicator of HPV. Therefore, the combination of cytology and molecular tests are the most important factors described at present for cancer prevention. An alternative study has analysed HPV serology and the cancer biomarkers of proteins p53 and p16, but no agreement on cancer prevention was achieved (Heilman & Kreinberg 2002).

In our study, due to the small sample size, a multivariate analysis was not performed. Thus, we have to consider the possibility that confounding variables led to altered prevalence results. In addition, other risk factors, such as the number of visits to gynaecological care and the interval between Pap tests, although recorded, were not evaluated in this article due to a great amount of misinformation during interviews and thus the data were discarded as incomplete or controversial.

As described in Table III, a highly significant factor associated with HPV infection in Group I was an age under 30 (PR = 3.1). Marital status was also frequently associated with infection (PR = 2.7), as well as ethnicity (PR = 5.2). HPV infection also prevailed in women with more than one sexual partner (PR = 8.4). Several authors have described similar results, especially in regards to the number of lifetime sexual partners (Bauer et al. 1993, Muñoz et al. 1996, Wang et al. 2003, Baseman & Koutsky 2005). We have chosen the criterion "one sexual partner versus more than one sexual partner" since women with a single long-term sexual partner were less likely to acquire sexually transmitted infections when compared to women who reported more than one partner (Pereira et al. 2007). For group II, a previous history of STD was significantly related to HPV infection (PR = 2.7) and this likely reflects other related risk factors, such as the number of sexual partners. It is important to note that infection by other genital pathogens also contributes to the risk of HPV infection by depressing local immunity. Nevertheless, co-infections in the genital tract can result in complex interactions between the different pathogens and the immune system of the host (Ferenczy et al. 2003), a discussion that is beyond the scope of this study.

A few studies have addressed the risk of smoking and infection and have found a significant correlation, attributed to a local impairment of cell-mediated immunity, but the effect of this was small (Burk et al. 1996, Wang et al. 2003, Stern 2005). In our statistical analysis, we found a significant correlation between the presence of HPV DNA and current smokers (PR = 2.0), but further studies concerning the amount of smoking per day are required to elucidate a possible relationship. Alcohol use, not only addiction, was significantly related to HPV occurrence in the genital tract (Table III). As previously proposed by Ho et al. (1988), alcohol use could alter social behaviour, leading to an augmented risk of exposure to STD-causing agents.

The peculiar results that were found for Group II suggested that the analysed co-factors can express the profile of this population, based on alcohol use and history of other STDs. In addition, the high prevalence described may be associated with other borderline variables, such as tobacco smoking, early beginning of sexual life and abortion, among others factors that are usually associated with poorer populations from developing countries. The finding of such diverse conditions and the risk of exposure within the same geographical region, poses a challenge to public health: to develop not only general but also specific strategies for screening all Brazilian women.

 

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Received 16 February 2009
Accepted 4 June 2009
Financial support: Faperj (E26/170-271/2006)

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