Located in the center of the city, Ghiesko (Haitian Group for Studies in Karposi's Sarcoma and Opportunistic Infections) is one of the first AIDS clinics in the world to be set up after the disease broke out in 1981.
Amid the surrounding rubble, and cries of desperation and chaos, it continues dispensing AIDS treatement to the thousands of people whose lives depend on it.
"It's a real pleasure for us health workers to see our patients come here despite what has befallen them," said nurse Naomi Jean-Charles as she renewed prescriptions and handed out pills to dozens of nervous people waiting in line.
"I'm surprised they're still coming. But one learns to work in situations of poverty caused by hurricanes and political unrest," said William Pape, the clinic's founder, who has moved the clinics operations to a wing of the building that survived the January 12 earthquake intact.
Supplied with medications by the Global Fund to Fight Aids, the US President's Emergency Fund for AIDS Relief (Pepfar), and the Merieux Institute, the clinic has never suffered an interruption in its stocks of antiretroviral drugs.
"The patients visit us each month and as a precaution we always give them a month a half's treatment so they won't run short," said Pape, who also teaches at Cornell University.
"What worries me more is not our usual patients but this horrible emergency situation, offering care to people who come in from all over with horrible injuries," he said.
Hundreds of injured Haitians have converged on the clinic in the nearly two weeks since the earthquake, along with some 5,000 homeless people who have taken refuge on land next to it.
A military hospital with a surgical unit has set up shop in a rear courtyard of the clinic, with the help from the US Health Department and American volunteer surgeons.
The 28 Ghiesko centers in Haiti care for half of all Haitians receiving anti-retroviral treatment, or about 12,000 patients, about 6,000 of them in the capital. About 300 people, including 18 doctors, work in the center in Port-au-Prince.
After the earthquake, the center broadcast reminders by radio to AIDS patients that their treatments were waiting for them in the capital or in the provinces, and it organized car pools to bring them from their neighborhoods.
"The war against AIDS, we are going to win it. The prevalence of HIV continues to fall in Haiti," Pape said.
It has fallen from 7.2 percent of the population in urban areas in the 1990s to 2.2 percent in 2009 with fewer than 150,000 people infected.
"The treatments are working," said Jean-Charles, the nurse, who said children born with HIV and who today are 30 years old come in regularly for their medications. "It is an achievement," she said with a smile.