Background:  AIDS-defining illnesses can occur after initiating HAART and more information can assist in clinical monitoring and targeted prophylaxis in resource-limited settings. This study aimed to determine the incidence and risk factors associated with the development of AIDS-defining illnesses after initiating HAART among South Indian patients.

Methods:  Participants included 1040 therapy-naïve patients initiating HAART between February 1996 and January 2007 with at least 18 months of follow-up at a tertiary HIV referral center in Chennai, India. Univariate and multivariate logistic regression models were used to examine the specific risks associated between the co-variates and the occurrence of infections.

Results:  Two-fifths of patients (40%) developed an AIDS-defining illness after initiating HAART:  11% developed an AIDS-defining illness within 3 months of initiating HAART. The highest incident illnesses within the first 3 months of initiating HAART included pulmonary tuberculosis (TB) (3%), extrapulmonary TB (2%), and cerebral toxoplasmosis (1.3%). The cumulative incidence at 18 months of the most common infections was pulmonary TB (5.4%), extrapulmonary TB (4.1%), and Herpes simplex (5.9%). Fewer than a tenth (3.6%) of patients who developed an AIDS-defining illness also developed IRS during the entire follow-up period. Of all patients who developed an AIDS-defining illness, 3% died. In univariate logistic regression, patients with CD4 cell counts below 100 cells/µL were 1.3 times more likely to develop an infection (95%CI 1.1 to 1.6), patients who experienced immunological failure were 1.5 times more likely to develop an infection (95%CI 1.3 to 1.8), and patients who had developed an adverse event to HAART were twice as likely to develop an infection (95%CI 1.8 to 2.6). These factors remained significant in multivariate logistic regression. 

Conclusions:  This study provides important information about the incidence of AIDS-defining illnesses at different levels of immunosuppression. The relatively high incidence of opportunistic infections within 3 months of initiating HAART demonstrates the possible lack of adequate immune reconstitution in this patient population and demonstrates the need for initiating ART earlier.