Viral subtype identification may be important because subtypes may differ in terms of the efficacy of potential vaccines, diagnostic testing for HIV infection, and monitoring of the health of HIV-infected patients. The report, by Tracy L. Sides, MPH, and colleagues of the Minnesota Department of Health and the HIV Program at Hennepin County Medical Center, emphasizes the need for better surveillance of HIV-1 subtypes to determine their prevalence.

For the first two decades of the AIDS epidemic in the United States, HIV-1 subtype B has been the predominant isolate throughout the country. In recent years, non-B HIV-1 subtypes have been spreading in parts of Europe. As Sides and colleagues explained, however, the prevalence of subtype B and other subtypes in the United States is not known, because subtype testing is not conducted with routine HIV/AIDS surveillance.

In 2003, the Minnesota Department of Health piloted HIV-1 subtyping with routine surveillance to describe and monitor non-B-subtype HIV-1 isolates. In Minnesota, African-born persons make up less than one percent of the population, but in 2002 accounted for 21 percent of the state's new cases of HIV infection. Accordingly, Sides and colleagues conducted targeted surveillance of 98 African-born HIV-infected patients to determine the existence and variety of HIV-1 subtypes. They also conducted surveillance on 28 non-African patients to monitor the introduction of non-B subtypes into Minnesota.

All of those infected with non-B subtypes were African immigrants attending health clinics in the Minneapolis-St. Paul area. Of the 98 African-born HIV-1-infected patients, 87 were successfully subtyped and 95 percent of these were infected with non-B subtypes. Seven different subtypes were identified, all consistent with strains endemic to the patients' regions of birth. Of the non-African HIV-1-infected patients, 25 were successfully subtyped and all were infected with subtype B.

The researchers believe that their results underestimate the prevalence of non-B subtypes in Minnesota because recent immigrants are less likely than assimilated immigrants to have access to the American health care system. Since their estimates are based solely on patients from health care facilities, they probably missed recent immigrants with HIV infection.

In an accompanying editorial, Diane Bennett, MD, MPH, of the Centers for Disease Control and Prevention explained that this study is important because few such investigations of U.S. subtype prevalence have been conducted, and because the results have national public health implications. "The findings of a high prevalence of non-B subtypes in a state where African-born individuals make up less than one percent of the population," she said, "suggest that it may be time to consider implementing HIV subtype surveillance in states with larger immigrant populations and throughout the United States."

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