HIV-positive patients who are coinfected with hepatitis C virus are significantly more likely to develop an AIDS-defining illness or experience a drop in their CD4 cell count to below 200 cells/mm³ than patients who are only infected with HIV, according to data from London's Chelsea and Westminster Hospital, published in the September 15 edition of Clinical Infectious Diseases (41:6, p. 906, 2005). The study, involving every patients who attended the Chelsea and Westminster Hospital since effective antiretroviral therapy became available and who underwent testing for hepatitis C, found that although the rate of CD4 cell count decline did not differ significantly between coinfected patients and those who were HIV-infected, patients who also had hepatitis C were significantly more likely to progress to AIDS. Although there is good evidence that HIV can worsen the course of hepatitis C virus-related disease, there are conflicting data concerning the impact of hepatitis C virus on HIV. Since the advent of effective anti-HIV treatment, liver disease caused by hepatitis C virus has emerged as a significant cause of illness and death in HIV-positive patients. Investigators from the London treatment centre therefore wished to compare rates of disease progression between patients coinfected with HIV and hepatitis C virus and those who were only infected with HIV.

The end points for the study were the onset of an AIDS-defining illness or a fall in CD4 cell count to below 200 cells/mm³. All patients presenting at the hospital with a CD4 cell count above 200 cells/mm³ since January 1996 were included in the study. A total of 5,800 patients were treated at the Chelsea and Westminster Hospital since effective anti-HIV treatment became available. Of these, 2,000 met inclusion criteria for the study and just under 1,500 of these individuals were tested for hepatitis C virus. A total of 85 patients tested positive providing a coinfection rate of just under 6%. Patients who were naive to antiretrovirals were significantly less likely to experience an event than patients taking anti-HIV therapy. This was because they had higher CD4 cell counts. Women were more likely than men to progress to AIDS or a CD4 cell count below 200 cells/mm³ (p = 0.034), and there was a 1% increase in risk for each one year increase in age. In multivariate analysis, the investigators found that patients who were coinfected with hepatitis C virus were 52% more likely to progress to AIDS or a CD4 cell count below 200 cells/mm³. However the rate of CD4 cell count decline was similar between HIV-infected patients and patients infected with HIV and hepatitis C virus.

"Although..analyses did not show any differences in CD4 cell count decreases between HIV-1-infected patients and patients with HIV-1-HCV coinfection, the groups differed with respect to the likelihood of having an event", comment the investigators. This suggested to them "that HCV infection is having an effect on HIV-1 disease progression that is not reflected in CD4 cell count." They suggest that this could be because hepatitis C virus was having an effect on CD8 cytotoxic T-cells or dendric cells. They conclude, "further effects of HCV on HIV-1 disease progression require additional clarification in large epidemiological studies."