Studies Confirm Rise of HIV Variant Strains in the United States and Importance of Reliable Viral Load Testing

Since the first diagnostic test for the human immunodeficiency virus (HIV) came on the market in 1985, public health authorities have been concerned about HIV's ability to mutate and create new strains of subtypes that may elude detection.

While many of the variant strains of HIV are not as prevalent in the United States as other countries, studies suggest that the influx of immigrants from countries where these strains are more common is increasing the number of newly diagnosed patients infected with variant HIV-1. If gone undetected, these variant strains of HIV could compromise treatment.

According to some studies, these infections, found mainly in immigrant populations from Africa and Asia, may represent up to 10 percent of HIV-1 infections in certain areas of the United States.

With the US launch of Abbott's RealTime HIV-1 viral load test, a highly sensitive test designed to detect and measure group M, N and O strains of HIV-1 as well as all known group M non-B subtypes, physicians now have a reliable test to help ensure that their patients are receiving the most effective treatment.

The test, marketed through Abbott's alliance with Celera, has been developed for use on Abbott's automated molecular diagnostics m2000™ system, based on real-time polymerase chain reaction (PCR) technology.

The test is intended for use as a marker of disease prognosis and as an aid in assessing viral response to antiretroviral treatment. Both the RealTime HIV-1 assay and the m2000 system are being showcased at the annual meeting of the American Association for Clinical Chemistry (AACC) in San Diego, July 15-19.

"With the increasing prevalence of HIV-1 non-B subtypes in the United States and other countries, it is critically important to have a reliable and accurate viral load test to monitor treatment efficacy and implement preventive measures for our increasingly diverse patient populations," said Linqi Zhang, Ph.D., associate professor and staff investigator, Aaron Diamond AIDS Research Center.

"Abbott has developed an assay with these considerations in mind, which will undoubtedly facilitate better treatment in both the developed and developing world."

HIV-1 can be divided into groups M (major), O (outlier) and N (new). The vast majority of isolates cluster in the M group, but the high mutation rate and rapid evolution of the virus has resulted in the emergence of different group M subtypes, designated A through K, and circulating recombinant forms.

A study by Dr. Zhang and his colleagues, focusing on the genetic characterization of HIV-1 strains circulating in immigrant populations in New York City, indicates that multiple subtypes of HIV-1 are present in these populations. The results of the study were published in the Journal of Acquired Immune Deficiency Syndrome in 2006.

"It is generally assumed that infections in the United States are exclusively with the B (subtype) and that this situation is going to continue into the foreseeable future," the authors wrote. "This study shows that this is unlikely to be the case and that non-B subtype strains already have a strong presence in the United States and have the potential for spreading in the future."

In another study by the Centers for Disease Control and Prevention earlier this year involving more than 3,000 HIV patients at 409 sites from 11 states, 5.1 percent of those patients were infected with HIV-1 non-B subtypes or a recombinant form (subtype C accounting for 2 percent and CRF02_AG accounting for 1.4 percent). The study demonstrated that the range of non-B subtypes and recombinant forms across the regions was 0 to 10.8 percent.

"Successful monitoring of people on HIV drug therapy mandates use of viral load assays to effectively identify and quantify all variant HIV-1 subtypes," said John Robinson, Ph.D., senior director, research and development, Abbott Molecular. "The reliability and precision of the Abbott RealTime HIV-1 test on the m2000 system for detecting HIV-1 subtypes across a broad dynamic range should help physicians be confident about assessing viral levels in their patients, enabling them to provide optimal treatment."