A Joint Modeling Approach to Assess the Impact of CD4 Cell Count on the Risk of Loss to Follow up in HIV/AIDS Patients on Antiretroviral Therapy

Lately, joint modeling has been reckoned as a very efficient technique for studying combinations of longitudinal and survival data generated from medical studies. In this paper we have developed a joint model to simultaneously study the longitudinal repeated measures on CD4 cell counts and the time to event (event being defined as loss to follow up) process of HIV/AIDS patients undergoing Anti-retroviral therapy (ART) treatment at Dr. Ram Manohar Lohia Hospital's ART centre, New Delhi, India. Apart from increasing the risk of the HIV infection to progress to AIDS, the event of loss to follow up in patients undergoing ART seriously interferes with the development, improvement, and validation of treatment techniques being used in the therapy. The fact that the problem of loss to follow up from ART has been understated in studies based on ART centers in India has motivated us to investigate the effect of various clinical, socioeconomic and demographic factors on the hazard of loss to follow up in patients undergoing ART treatment. The results of the joint model have been compared with those of the separate analyses of the longitudinal and the survival data. The parameter estimates of both methods are consistent; however, the joint analysis supports the dependence of the hazard of lost to follow up from ART treatment on the rate of change in CD4 counts, apart from the patient's baseline CD4 count. The estimated overall survival probability for HIV/AIDS patients retained on antiretroviral therapy was 0.81; 95%CI (0.76- 0.87).