TYPE C HEPATITIS VIRUS (HCV) has been recognized as the cause of most cases of non-A, non-B hepatitis in developed countries. Transfusions with blood and blood products are documented risk factors,1,2 and parenteral use of drugs also represents a major route of HCV transmission.3 Nevertheless, over 40% of HCV-infected individuals have no reported risk factors for parenteral exposure, suggesting that other routes of transmission are involved in the spread of the virus.4
Specifically, the role of sexual contact still needs to be defined, although it is accepted that sexual transmission may infrequently occur. Several studies have explored the hypothesis of sexual transmission of HCV infection, reporting that HCV prevalence was 4 to 15 times higher among homosexual men and heterosexual non-intravenous drug users (non-IDU) with multiple partners5–7 than in the general population.8 Studies conducted on non-IDUs attending clinics for sexually transmitted diseases (STD) have shown prevalences of HCV antibodies ranging from 5.2% to 9.7% and have found associations with unprotected sexual intercourse,9 anal receptive intercourse,10–12 and number of lifetime sexual partners.13 Also, specific STDs such as genital herpes simplex virus type 2,14,15 syphilis,12 and human immunodeficiency virus type 1 (HIV-1) infection13 have been found to be associated with an increased risk of HCV seropositivity. Nonetheless, the presence of HCV in semen and in other biologic fluids involved in sexual intercourse has not been definitely demonstrated to date.16–19 Furthermore, there is a lack of information on the risk of sexual transmission of HCV because of the limited number of longitudinal studies conducted.
To understand better the role of sexual behavior in HCV transmission, we enrolled a cohort of HCV-negative individuals attending a voluntary HIV-1 testing program in a large STD clinic in Rome. The principal goals of the study were to estimate the incidence of HCV infection in individuals considered to be at high risk for STDs and to identify possible risk factors for seroconversion.
We studied a cohort of individuals at risk for HIV-1 infection and STDs (homosexual and bisexual men, IDUs, and heterosexual individuals with multiple partners) attending a large municipal STD clinic in Rome, Italy, from June 1, 1992 to December 31, 1994. Information on behavioral risk factors was collected by a standard interview conducted during the HIV pretest counseling session. The interview included questions on demographic characteristics, age at first sexual intercourse, contraceptive and condom use, sexual practices in the past 6 months, and history of STDs and of injecting drug use. A serum sample for HCV, hepatitis B virus (HBV), and HIV-1 serologic testing was taken from all participants during each consultation. Non-IDU heterosexual individuals were defined as those not reporting intravenous drug use or homosexual contacts.
A retrospective longitudinal study was conducted. All individuals with a first negative HCV antibody test who underwent at least one additional test during the study period were included in the study. Participants who had received a blood transfusion either before or during enrollment were excluded from the data analysis.
Sera from all participants were tested with a second-generation enzyme immunoassay (EIA 3.0; Abbott, Wiesbaden, Germany) for HCV antibodies. All EIA-reactive results were confirmed using a second-generation fourband recombinant immunoblot assay (RIBA 2; Deciscan HCV; Sanofi-Pasteur, Paris, France). Sera were also tested for HIV-1 antibodies using an enzyme-linked immunosorbent assay (ELISA Genelavia Mix; Pasteur, Paris, France); HIV-1-reactive sera were confirmed using a Western blot test (NevLav Blot I; Sanofi-Pasteur). For HBV antibodies, an EIA was also used (Sorin; Biomedica Diagnostics, Turin, Italy).
Incidence rates were calculated using the person-time method for the total population and by exposure category. HCV seroconverters were compared with persistently HCV-negative individuals for selected clinical and behavioral characteristics, using a nested case-control analysis. Risk factors for HCV seroconversion were assessed, calculating odds ratios with 95% confidence intervals (CI95%) from 2 × 2 tables. Multivariate analysis using the Cox proportional hazards statistical model20 was performed to assess the independent role of variables identified at the univariate analysis. Data analysis was performed using the SAS Statistical Software System (SAS Institute Inc., Cary, NC). Only for HIV-1-infected individuals were crude incidence rates of HCV infection calculated by the level of immunosuppression. To this end, HIV-1-infected individuals were stratified into three groups on the basis of the degree of immunosuppression: mild immunosuppression (CD4+ cell count > 500 cells/mm3), moderate immunosuppression (201–500 cells mm3), and severe immunosuppression (≤ 200 cells/mm3).
Between June, 1992 and December, 1994, 709 HCV-seronegative individuals were enrolled. With regard to the exposure categories, 453 (63.5%) individuals were heterosexual non-IDUs, 244 (34.4%) homosexual men, and 12 (2.1%) IDUs.
The median age of the participants was 35 years (range: 18–62 years). At baseline, 116 (16.4%) individuals were HIV-1 positive. The median numbers of consecutive HCV tests was 2.5 for heterosexual non-IDUs and 4 for IDUs and homosexual men. No significant differences were found with respect to the number of consecutive HCV tests between HIV-infected and noninfected participants.
A total of 15 HCV seroconversions occurred during the study period. The mean duration of follow-up was 1.25 person/years (p/y), with an overall incidence rate of 1.69 per 100 p/y. Most of the individuals who seroconverted to HCV were men (n = 11; 73.3%), with a median age of 36.8 years and an incidence rate of 1.29 per 100 p/y. Among the 15 HCV seroconverters, 10 (66.6%) were non-IDUs: 5 heterosexual non-IDUs and 5 homosexual men.
The incidence rates varied by specific exposure category. Among IDUs, the incidence was 39.30 per 100 p/y, among homosexual men it was 1.37 per 100 p/y, and among heterosexual non-IDUs it was 0.97 per 100 p/y.
With regard to risk factors for HCV infection, univariate analysis showed an association between HCV seroconversion and parenteral drug use and between HCV and HIV-1 seropositivity at enrollment; a marginal association with history of STDs was also found (Table 1).
Two multivariate logistic regression models for HCV seroconversion are shown in Table 2. Model I, which includes the 12 IDUs, showed a strong independent association of HCV seroconversion with parenteral drug use (relative hazard [RH] = 10.08; CI95% = 1.08–93.92) and a marginal association with HIV-1 seropositivity (RH = 3.35; CI95% = 0.53–21.08), after controlling for age, gender, number of sexual partners, condom use, and current and previous STDs.
After excluding the IDUs, model II showed that among the 697 non-IDUs, only HIV-1 seropositivity tended to be associated with an increased risk of HCV seroconversion (RH = 5.48; CI95% = 0.85–35.40).
Among the 116 individuals who were HIV-1 infected at time of enrollment, 6 (5.2%) HCV seroconversions occurred: 3 in IDUs, 2 in homosexual men, and 1 in heterosexual non-IDUs. After stratifying the 114 individuals with known CD4+ cells count by degree of immunosup-pression, the HCV crude incidence rate was 11.5% (3/26) for HIV-1-infected individuals with severe immunosuppression, 4.2% (2/47) for those with moderate immunosuppression, and 2.4% (1/41) among those with mild immunosuppression; however, the trend was not statistically significant (chi-square for trend = 2.38, P = 0.1).
In terms of morbidity and mortality, viral hepatitis represents one of the most important STDs worldwide, although sexual transmission has been well documented only for HBV.21 For HCV infection, the risk of transmission through sexual intercourse has not yet been well defined, and the controversial results of several studies have limited the adoption of preventive guidelines for health education and counseling.
Several European studies have shown a prevalence of HCV antibodies of 2% to 4% among homosexual men attending STD clinics.22–24 In Italy, a study conducted among homosexual men suggested that the risk of HCV infection is 4 times higher for individuals with HCV-positive partners, compared with those with a monogamous sexual relationship with an HCV-negative partner, and 2.6 times higher among those with over 20 occasional partners/year, compared with those with less than 20.25 Moreover, two other Italian studies conducted among heterosexual partners of HCV-positive individuals with clinical signs of hepatitis showed high HCV prevalences (13% and 17%)26,27; these data were confirmed by those from other studies conducted abroad in the same types of population groups.28,29
To date, very few longitudinal studies have been conducted to assess the occurrence of HCV infection among STD patients and the current study constitutes one of the few attempts to assess risk factors for HCV seroconversion using incident cases of infection. In this study, the incidence rate among IDUs was slightly higher than that reported in a previous study conducted among IDUs attending three drug treatment centers in Naples.3
Parenteral drug use was confirmed to be the strongest determinant of HCV infection, even in population groups at risk for STDs. Nonetheless, the relatively high incidence rate of HCV seroconversion among non-IDUs at risk for STDs confirms that sexual behavior may play a role in HCV transmission.
Univariate analysis showed that HCV seroconverters were more likely to be HIV-1 positive. The RH did not change at the multivariate analysis, but the association became marginally significant because of the limited power of the study. Moreover, HIV-1-infected non-IDUs were over five times more likely to develop HCV antibodies than HIV-1-seronegative non-IDUs, although the difference did not reach statistical significance.
The mechanisms through which HIV-1 may facilitate the sexual acquisition of HCV are not clearly understood, although some hypotheses can be proposed. HIV-1-induced immunosuppression may increase the biologic susceptibility of the HIV-1-infected host. Our study seems to support this hypothesis, showing increased crude incidence rates among HIV-1-infected individuals with severe immunosuppression (11.5%) compared with individuals with moderate (4.2%) and mild immunosuppression (2.4%).
Nonetheless, it is possible that HCV infection may have been transmitted by HIV/HCV-coinfected individuals. In fact, HIV-1-infected individuals could have a greater capacity to transmit HCV infection than HIV-1-negative individuals because of enhanced levels of HCV viremia in the serum and biologic fluids related to the HIV-1-induced immunosuppression, as suggested by mother-to-child HCV transmission.30 However, the HIV serostatus of the sexual partner was not available for all study participants. Finally, it is possible that individuals with a high frequency of risk behavior may acquire HCV and HIV-1 infection independently.
Before drawing conclusions, some limits and biases of the study should be mentioned. The limited power because of the relatively small number of HCV seroconversions may have determined the lack of statistical significance of some associations, although the relative risk was high. Furthermore, incidence rates may have been somewhat biased because of self-selection mechanisms. In fact, individuals undergoing at least two successive tests may not be representative of the total population of STD clinic attendees, especially of all those undergoing HIV testing.
In conclusion, our longitudinal study confirms that injecting drug use is the most important determinant of HCV infection. However, sexual transmission may occur at relatively high rates and seems to be influenced by the HIV-1 serostatus of the host. HIV-1 immunosuppression could facilitate the acquisition of HCV infection. Further longitudinal studies on discordant couples are needed to evaluate the consistency of our results and to confirm our hypotheses.
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