The men show up on foot, on bicycles, by van or car.

Before entering the sky-blue door at the rear of the vast office plaza, they carefully look around to make sure no one is watching them go in.

Behind the door, authorities say, is a Medicare racket. Manassas Medical Center in Doral has billed the taxpayer-funded insurance program for therapy that patients with HIV or AIDS haven't received.

Among the men stepping in on a June morning is Alexander McCray, who regularly stops at Manassas and dozens of Miami-Dade clinics.

McCray, a 40-year-old Opa-locka resident, admits he pockets thousands of dollars in kickbacks in exchange for giving the clinics his Medicare number to bill the agency for phony HIV infusion treatments. Manassas is among hundreds of Medicare-licensed clinics in South Florida that defraud the system with fake HIV-drug claims, according to federal claim records and authorities.

The scams are especially outrageous because HIV infusion therapy, which entails intravenous drips of medication to boost a patient's immune system, has been replaced almost everywhere but South Florida by more effective antiretroviral drugs taken orally. Yet Medicare has continued to allow the outdated HIV infusion services and to pay hundreds of millions of dollars for the treatments because the agency still considers them ``reasonable and necessary.''

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