Estimating the Duration of the Sojourn and the Change in Clinical Conditions for HIV Patients Receiving ART Follow-up in Namibia

This chapter introduces a Semi-Markov process for estimating sojourn time and transition between clinical states of HIV patients under ART follow up. A Semi-Markov process under HIV disease progression can be defined based on the distribution of sojourn times. Sojourn time refers to the amount of time a HIV patient spends in each clinical state in a single stay before he/she makes a transition to another state. HIV disease progression can be broken down into a number of intermediate states, based on CD4 counts. The four states of the Markov process of HIV are commonly defined as: S1: CD4 count > 500 cells/microlitre of blood; S2: 350 < CD4 count 500 cells/microlitre of blood; S3: 200 < CD4 count 350 cells/microlitre of blood; S4: CD4 count 200 cells/microliter of blood. The main objective of this chapter to estimate sojourn and transition between clinical states of patients under ART in Namibia using homogenous semi-Markov processes, on data obtained from Ministry of Health and Social Services (MoHSS), Namibia. It is essential to state that during the follow-up period, no death was recorded and this could be attributed to intensive efforts by the government and various stakeholders. Namibia is the first African country to have reached and exceeded the UNAIDS 2020 goal, to have at least 73% of HIV positive adults viral load suppressed. In this chapter, a retrospective study design was used to obtain data on 2422 patients who were observed 11028 times, during 2008 to 2017 follow up period. The four staged semi-Markov model was employed to estimate sojourn times and transition between clinical states. By the end of the chapter, the main results of the study are given; this includes descriptive statistics on socio-demographic characteristics of the patients, probabilities of transiting from one state to another and sojourn times for each state. Furthermore, a full discussion of the main results is provided. Conclusion is given to reflect on the evidence and to account any limitation of the study. Specific actions that can be taken based on the results and conclusion are included.