A Probability Model for Estimating the Force of Transmission of HIV Infection and Its Application

Information on force of transmission of HIV infection is crucial for better understanding of the epidemic. It is useful for better programme planning and evaluation. The current study aims at fitting probabilistic models for estimating the force of transmission of HIV infection due to different risk behaviour, heterosexual/homosexual/IDUs. The force of transmission between the risk groups bridging the infection is obtained as the joint probability function of the growth probabilities of HIV positivity over time among them. The growth probabilities of HIV positivity is estimated by fitting appropriate probability distributions to observed data from HIV Sentinel Surveillance (HSS) in Andhra Pradesh, India. The joint probabilities are estimated assuming that the risk behavior among the groups is random and the growth of infection within each group is independent in a region. In the study population, the average force of transmission is estimated to be 3.4755E-09 among general population, 1.5508E-03 among MSMs and 4.8455E-03 among IDUs, and 2.132E-03 in the total population. The results are subsequently used to estimate the HIV burden and compared with the estimates derived by other approaches.