Hepatitis C Virus-Specific Immune Responses in Noninjecting Drug Users

From Journal of Viral Hepatitis

Hepatitis C Virus-Specific Immune Responses in Noninjecting Drug Users

M. Zeremski; J. Makeyeva; K. Arasteh; D. C. Des Jarlais; A. H. Talal

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Abstract and Introduction
Materials and Methods

Discussion 

Results

Discussion Only

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In this study, 19.3% of analyzed  noninjection drug users - NIDUs were found to be HCV seropositive, while 9.8% had detectable, although weak HCV-specific cellular immune responses. Overall, 27.5% of study participants had either HCV-specific antibodies or cellular immunity, which is considerably higher compared to the general population in which HCV prevalence is estimated to be 1.7%.^[3] Our findings are well within the 2–35% HCV seroprevalence range previously reported among noninjection drug users - NIDUs.^[11]

Surprisingly, we did not find any associations between patterns of noninjecting drug use behaviours and HCV-specific immune responses. However, we identified multiple associations between HCV-specific immunity and sexual behaviours, including having more casual opposite sex partners, having sex partners who had ever injected drugs, buying sex, and ever having male-to-male sex.
We believe our findings do not necessarily indicate that HCV exposure occurred only though sexual activities among our subjects. Our measures of both sexual and noninjecting drug use behaviours covered only 6 months prior to the interview, and most HCV exposures probably occurred years earlier. Additionally, having an IDU sexual partner suggests a very high likelihood of contact with an HCV-infected individual. NIDUs with IDU sexual partners may engage in noninjecting drug use and sexual activities simultaneously, which is particularly common when stimulants, such as crack cocaine, are taken.^[26] In such a case, it would be difficult to ascertain which of the two behaviours transmitted HCV. The use of stimulant drugs may also prolong sexual intercourse,^[27] while their vasoconstricting effects may decrease recto-vaginal secretion, consequently enhancing the possibility of tissue abrasions that can lead to blood-to-blood contact and HCV transmission.

In this study, none of the subjects had both HCV-specific antibody and cellular immunity. Of 11 seropositive individuals, 7 had chronic HCV infection while 4 had spontaneously cleared the infection. In general, individuals who do not eradicate HCV have weak or undetectable HCV-specific T-cell responses, which is partially the reason for HCV persistence.^[28] Consequently, our finding of negative ELISpot results in patients with chronic HCV infection is not surprising. Additionally, our previous work showed that almost half of IDUs who spontaneously cleared HCV do not have detectable T-cell responses.^[23] Therefore, as we were unable to perform the ELISpot in two of our NIDU subjects with spontaneous HCV resolution, a lack of overlap between detectable cellular and serologic HCV-specific immune responses in our study population is not unexpected.

Limitations of this work include the relatively modest number of subjects, which may have impacted on our ability to detect significant associations between noninjection drug use patterns and HCV-specific immunity. Our questions covered the preceding 6 months, while HCV exposure probably happened much earlier. Consequently, meaningful associations would occur only if recent behaviours represented long-standing patterns. Lack of questions regarding tattoos, body piercings or blood transfusions, all associated with HCV acquisition, is another limitation of the study. Finally, our behavioural data were based on self-reports, and thus are subject to possible social desirability bias. In particular, some subjects might have injected drugs, but denied doing so during the interviews. However, we did find multiple relationships between HCV immunity and socially undesirable behaviours, e.g. reporting paying for sex, which suggests that social desirability did not completely obscure relationships between behaviour and HCV exposure.

In summary, we found HCV prevalence to be much higher in this cohort of NIDUs compared to that in the general population. HCV seroprevalence was not associated with recent noninjection drug use practices and was associated with recent sexual behaviours. However, given the likely overlap between sexual and drug use partners, we believe that both noninjection drug use and sexual behaviours should be considered potential routes of HCV transmission. We would note the great difficulties in trying to separate sharing of noninjecting drug use equipment from sexual intercourse as routes of HCV transmission among NIDUs. Even though HCV prevalence is clearly elevated among NIDUs, exposure to HCV is still a relatively rare event. Thus, large number of patients would need to be followed for long periods of time in order to identify specific drug use and sexual behaviours associated with HCV exposure among NIDUs. Until additional studies are conducted, we would suggest warning NIDUs that HCV might be transmitted through both sharing of drug equipment and through sexual activity.