Estimates of opportunistic infection incidence or death within specific CD4 strata in HIV-infected patients in Abidjan, Côte d’Ivoire: impact of alternative methods of CD4 count modelling

CD4 lymphocyte count is an important surrogate marker of HIV disease progression, but it is often unavailable at the time of clinical events. We analysed data from the Cotrame cohort (1999–2004) and the Trivacan Structured Treatment Interruption trial (2002–2005) to estimate the incidence of opportunistic infections and death within specific CD4 strata in HIV-infected patients receiving highly active antiretroviral therapy (HAART) in sub-Saharan Africa. We used three methods of CD4 modelling: the first assumed that CD4 cell count remained constant until the next measurement; the second assumed that it changed immediately to the level of the subsequent measurement; and the third assumed that it followed a linear function between two consecutive CD4 measurements. The cohort used in this analysis consisted of 981 patients. The incidence rates of opportunistic infections were highest in the lower CD4 strata and decreased in the higher CD4 count strata. The incidence rates of mild opportunistic infections and severe bacterial infections, however, remained high in the highest CD4 stratum. Although all confidence intervals overlapped among the three methods, the incidence rate estimates showed differences of up to 74% in the lowest CD4 stratum. Different methods of estimating CD4 counts at the time of clinical events led to minor differences in incidence rates, except in the CD4 stratum <50 cells/mm3, where the follow-up time was shorter. All of the models indicate that the overall incidence of opportunistic infections under HAART in sub-Saharan Africa is high. This suggests that prophylaxis against opportunistic infections may be needed even for patients receiving HAART.