In this large sample of HIV-infected and high-risk HIV-uninfected women, we found that among women who self-reported no history of IDU, sex with an IDU male was independently associated with prevalent HCV infection after controlling for receipt of blood transfusion, older age, unemployment, smoking, birth in the United States, and hepatitis B infection. This effect was statistically significant only for the HIV-infected although no statistically significant interaction was noted. While this study is cross-sectional, it is possible that HIV infection may play a role in increasing the likelihood of HCV sexual transmission because of a compromised immune system in the setting of continued high-risk sexual behaviors.
In this study group, the prevalence of HCV infection among women with no reported history of IDU or receipt of blood transfusion was 6.5% (3.6% for the HIV− and 7.7% for the HIV+). Because of the large proportion of HIV-infected women in our study with high-risk behaviors for both HIV and HCV infection, this prevalence is higher than has been reported for other high risk groups such as patients at two large STD clinics in Canada (3.4%), a sample of sexually active, nontransfused, inner-city women with no evidence of IDU (1.6%), and among women residing in low-income neighborhoods of northern California (2.5%).1,8,25
In the United States, it is estimated that IDU accounts for approximately 60% of HCV transmissions, blood transfusion for less than 5%, sexual exposures approximately 10%–20%, other exposures 10%, with 10% due to unidentified sources of infection.2
In our cohort of HCV positive women, 86.5% reported exposure through parenteral routes leaving 13.5% potentially due to other exposures, including sexual transmission.
Consistent with other studies, we showed that risk-taking behaviors including history of drug use (including crack, cocaine, and heroin), smoking, drinking, and high-risk sex (trading sex for drugs or money, sex with an HIV-positive male, more lifetime sexual partners and STDs) were associated with a higher prevalence of HCV infection.7,10,25–28
A recent study of risk factors associated with acute HCV infection found that 11 of 13 cases with unknown mode of transmission reported high-risk sexual behavior.29
While it has been demonstrated among married couples with one HCV-infected member that HCV sexual transmission is not efficient,30
molecular epidemiologic studies have nonetheless shown that HCV RNA can be detected in the semen of HCV viremic men, and men coinfected with HIV are more likely to have HCV RNA detected in the semen than men with only HCV infection.15,31–33
Only further studies using experimental infection in a cell culture system or an animal model would prove that HCV RNA positivity in semen reflects the presence of infectious virus.
Further study of the sexual practices of women with HIV and at risk for HIV may shed light on potential mechanisms of sexual transmission of HCV. Like HIV, STDs may increase the risk of HCV transmission through ulcerative lesions, providing a portal of entry for HCV. Anal sex, intercourse during menstruation, and sex with physical trauma may also provide avenues for enhanced sexual transmission of HCV through exposure to blood. Among HIV-infected MSM, it has been suggested that high-risk sexual practices including anal fisting and sex in the presence of ulcerative coinfections are associated with HCV acquisition and may have fueled recent HCV outbreaks in this subgroup of MSM.34,35
These same mechanisms may be important for HCV transmission among HIV-infected women engaging in high-risk sexual practices.36
Our study supports earlier findings of Hershow37
et al. in 1998 who evaluated a subgroup of the WIHS cohort (n
296) and found as we did that while IDU was the strongest predictor of HCV infection, sexual risk factors were also independently associated. Our analyses expand on their work by examining the entire WIHS group. While Hershow found only a marginally significant effect of HIV status, we found a statistically significant effect of HIV status for both those with and without IDU.
Because IDU was defined by self-report, it is possible that some women classified as non-IDU chose not to report their own IDU. We attempted to minimize this possible misclassification by excluding 12 women who reported no baseline IDU but later reported IDU at a subsequent WIHS visit. Analysis of the WIHS longitudinal data through 2004 showed overall consistency in reporting of IDU over time. Only 0.5% (12/2522) of the non-IDU women at baseline reported IDU during a follow-up visit compared to 39% of those with IDU at baseline. Of these 12 women, four reported IDU within 1 year of the baseline visit, two within 2 years, and the remaining six reported IDU 5 or more years after the baseline visit. While these 12 women did not differ from the total population by HIV status, age or HCV status, they were removed from the analysis because of the potential for misclassification of their baseline IDU status. Prior studies have also shown that self-reported information from WIHS participants correlates with appropriate biologic markers.38
While IDU women are known to partner with IDU men, studies of sexual behaviors of IDU men have found that they commonly choose non-IDU women as their sex partners.39,40
Neaigus et al. have recently shown that HIV-infected injecting and non-injecting male drug users were more likely to have lower risk sexual partners (HIV- and non-IDU) than high-risk partners, creating a potential bridge for STDs diseases from a high-prevalence to a low-prevalence population.41
Consistent with other studies we found that HCV was associated with older age, birth in the United States, level of education, poverty, hepatitis B infection, and being HIV-infected.1,10,25–27
Being unemployed has not previously been reported as a factor associated with HCV, although low socioeconomic status and poverty have been described as risk factors.8,18,25,28
It is possible that being unemployed may be related to poor health and greater risk-taking behaviors and thus a greater susceptibility to acquiring HCV through both parenteral and nonparenteral means. Further work is needed to determine the specific types of sexual activity that might predispose to HCV transmission.
Limitations of this study include the potential for underreporting STDs, risk behaviors and recall bias, particularly regarding IDU, STDs, and sexual behaviors. Our study did not address specific sexual habits that may increase HCV transmission risk as well as other possible risk factors for transmission, including sharing of razors or toothbrushes, receipt of tattoos, or body piercings. Data regarding cohabitation where these issues could have been explored were not collected in WIHS. Similarly, data were not collected regarding the sharing of straws or other devices to snort drugs, which have been hypothesized as potential mechanisms for HCV transmission through hyperemic and traumatized nasal mucosa. Importantly, this was a cross-sectional analysis of prevalent HCV infection and thus, no conclusions can be made about the risk factors for acquiring HCV infection over time. In IDU populations, the time since first injection is frequently used to judge length of HCV infection because HCV transmission risk is high due to very high blood HCV levels. However, similar assumptions cannot be made with sexual transmission as the risk following sexual exposure is much lower than following blood exposure, most probably since genital HCV levels are very low or undetectable.42,43
Finally, another limitation of the study is the possible underestimation of HCV among the HIV-positive women because of the higher rate of false-negative HCV antibody tests in this population, particularly those with IDU and CD4 cell counts <200
While in the United States HCV infection due to blood transfusions is diminishing due to blood screening, HCV is still a major public health concern. Use of injection and noninjection drugs is still a major problem and is associated with trading sex for drugs or money and engaging in risky sexual behaviors. Concerns about the higher HCV prevalence and increasing HIV rates in Hispanics, who are the fastest growing ethnic minority group in the United States, should alert public health officials to the importance of the potential for sexual transmission of HCV.46
Similarly, in the United States, HCV prevalence rates are highest for non-Hispanic black men between 40–49 years of age raising concern about the potential transmission of HCV to their sexual partners who might engage in high-risk sexual behaviors.1
In conclusion, our study demonstrates an overall HCV prevalence of 6.5% among HIV-infected and high-risk HIV-negative women without a history of IDU or receipt of blood transfusions. In multivariate analyses, older age, birth in the United States, unemployment, hepatitis B, HIV coinfection, and sex with an IDU were associated with HCV infection. Further study of other factors that may increase HCV transmission may provide important information regarding the mechanisms of HCV transmission and how to prevent such transmissions among HIV-infected women with multiple risk factors.