Superinfection with drug-resistant HIV: case reported

A case of superinfection with a drug-resistant strain of HIV is reported in the August 12^th edition of AIDS. The case involves a 31-year-old gay man in San Diego, California, who was initially diagnosed with a drug sensitive strain of sub-type B HIV but was subsequently discovered to have been superinfected with a strain of sub-type B resistant to two classes of antiretroviral drugs. Superinfection resulted in a significant increase in the individual’s viral load and a fall in his CD4 cell count.

Although it has been suggested that HIV superinfection occurs frequently, there have been few documented cases. The cases which have been identified involve patients who were initially infected with drug resistant HIV and were subsequently superinfected with a wild-type, or drug sensitive strain of the virus.

In the autumn of 2001 a 31-year-old gay man was referred to San Diego Acute HIV Infection and Early Disease Research Program after recently testing HIV-positive. He had previously had a negative HIV test in the late 2000 and had had symptoms suggestive of primary HIV infection in the spring of 2001. Repeat HIV testing in September 2001 indicated that he had, indeed, been infected with HIV in the last six months. Genotypic and phenotypic tests found no primary resistance mutations, and the individual had a CD4 cell count of 571 cells/mm³ and a viral load of 1200 copies/ml.

For nine months the patient’s viral load remained stable. However, it subsequently leapt to 11,600 copies/ml and four months later increased to 142,000 copies/ml. Coinciding with this was a drop in the man’s CD4 cell count by 150 cells/mm³.

One month later he entered a clinical trial investigating the safety and effectiveness of Trizivir (AZT, 3TC, abacavir). The man’s viral load was never suppressed below 50 copies/ml and he reported sub-optimal adherence throughout the four months he was on the study.

Resistance tests after four months found resistance to protease inhibitors, even though the patient had never taken these. However, the patient did report frequent unprotected anal sex since his initial HIV diagnosis.

To establish possible superinfection, the investigators employed four testing techniques using blood samples obtained 260 days apart –drawn when the patient was first seen at the centre and again when the increase in viral load and fall in CD4 cell count suggested that superinfection had occurred.

Tests indicated that the patient had been infected with two distinct strains of HIV sub-type B indicating that this was a case of superinfection rather than coinfection (initial infection with two distinct HIV strains).

Resistance to protease inhibitors and drugs from the nucleoside analogue class was identified.

“This superinfection negatively affected this subject’s disease and course of treatment”, comment the investigators. They conclude, “HIV drug resistance acquired through superinfection significantly lowers the likelihood of successful antiretroviral therapy. It undermines the clinical value of a patient’s prior drug resistance testing and lack of antiretroviral use.”