JOHANNESBURG — In the early 1990s when South Africa’s Themba Lethu clinic could only treat HIV/AIDS patients for opportunistic diseases, many would come in wheelchairs and keep coming to the health center until they died.

Two decades later the clinic is the biggest antiretroviral, or ARV, treatment center in the country and sees between 600 to 800 patients a day from across southern Africa. Those who are brought in wheelchairs, sometimes on the brink of death, get the crucial drugs, and often become healthy, and are walking within weeks.