Estimating sexual transmission of HIV from persons aware and unaware that they are infected with the virus in the USA

BACKGROUND: New HIV infections stem from people who are aware they are HIV positive (approximately 75% of infected persons in the USA) and those who are unaware of their HIV-positive status (approximately 25%). OBJECTIVE: We estimated the relative contribution of these two groups in sexually transmitting new HIV infections to at-risk (HIV-negative or unknown serostatus) partners in the USA. METHODS: The parameters in the estimation included: number of people aware and unaware they are infected with HIV; 33% of the aware group are at low risk of transmitting HIV because of low/undetectable viral load; 57% relative reduction in the prevalence of unprotected anal and vaginal intercourse (UAV) with at-risk partners in persons aware (compared to unaware) they have HIV; and assumed differences in the average number of at-risk UAV partners in each awareness group (ranging from equal to twice as many in the unaware group). RESULTS: The proportion of sexually transmitted HIV from the HIV-positive unaware group was estimated to range from 0.54 (assuming no difference in average number of at-risk UAV partners between groups) to 0.70 (assuming twice as many at-risk UAV partners in the unaware group). Using the lower bounds, the transmission rate from the unaware group was 3.5 times that of the aware group after adjusting for population size differences between groups. CONCLUSION: The results indicate that the HIV/AIDS epidemic can be lessened substantially by increasing the number of HIV-positive persons who are aware of their status.