The natural history of antibody responses to Cryptosporidium parasites in men at high risk of HIV infection

Background. Although the clinical severity of cryptosporidiosis is altered by human immunodeficiency virus (HIV)-related immunosuppression, little is known about how risk for Cryptosporidium infection is altered by HIV. Methods. A retrospective cohort study was conducted among 78 participants of the San Francisco Men's Health Study, using stored serological specimens from 8.5 years of follow-up. Cryptosporidium infection was defined as an antibody response to both the recombinant 27-kDa (r27) and native Triton-extracted 17-kDa (TX17) Cryptosporidium antigens. Results. Cryptosporidium infections were detected more frequently by assessment of antibody responses than by routine clinical follow-up (195 [95% confidence interval {CI}, 154-241] vs. 11 [95% CI, 3-30] infections/1000 person-years, respectively). HIV-positive individuals (59%) were more likely than HIV-negative individuals (30%) to have had at least 1 serologically defined infection (P=.028). The estimated infection rate was 230 (95% CI, 175-293) infections/1000 person-years and 140 (95% CI, 86-210) infections/1000 person-years for HIV-positive and HIV-negative individuals, respectively. Median decay time to half-life ranged from 13.8 to 15.1 months. Conclusions. Our study emphasizes that Cryptosporidium infections are common in this population. Although HIV status altered the risk of Cryptosporidium infection, further studies are needed to adequately examine the effect of CD4 cell count.