STD Quarterly-Testing strategy gives look at HIV incidence
When it comes to distinguishing new HIV infections from longstanding infections, public health officials are looking to the STARHS — the Serologic Testing Algorithm for determining Recent HIV Seroconversion.
Developed by scientists at the Atlanta-based Centers for Disease Control and Prevention (CDC) along with other colleagues, the STARHS technology allows researchers to determine whether infection occurred in the last four to six months. With this testing strategy, public health officials can begin to know which populations are becoming HIV-infected today and how to help stem further spread of the disease.
"First and foremost, it is most useful as a tool to help us measure incidence," says Sandra Schwarcz, MD, MPH, director of AIDS surveillance with the San Francisco Department of Public Health. "What is particularly exciting about it is that it allows us to measure incidence in a cross-sectional survey, at a single point in time, and that has not been possible before."
The STARHS strategy uses two separate HIV antibody tests. The first test is the standard antibody test, the enzyme-linked immunosorbent assay (EIA). It is used to detect the presence of HIV just six to eight weeks after infection.
The second test is a less sensitive, or detuned, form of the standard antibody test. Because people who have been infected recently (those who have seroconverted within the previous four months) have lower levels of antibody, they will test seropositive on the standard, sensitive EIA and seronegative on the less sensitive EIA. People with long-standing infections (defined as those who have seroconverted sometime before the previous four months) will have antibody levels sufficiently high to test positive on both of the assays.1
The ability to determine early HIV infection means the identification and notification of previous sexual and needle-sharing partners can be enhanced, say public health officials.1 Early detection also may have positive implications for medical treatment and may strengthen HIV epidemiological surveillance.
For some time, CDC researchers had been looking at easy ways to measure HIV incidence and measure new infections, says Robert Janssen, MD, deputy director of the Division of HIV/AIDS Prevention — Surveillance and Epidemiology. This had proven to be no simple task, as scientists were unable to use a number of markers to determine new infections.
At the same time, researchers were examining methods to confirm the safety of the blood supply. CDC mathematical statistician Glen Satten, PhD, came upon the idea of using older, less sensitive assays to identify people early in infection, Janssen recalls.
"Even though they [the older assays] were pretty good, there was still a period during which someone would be reactive on the new assay but not reactive on the old assay," Satten explains. "Presum ably, the first assays were made to be as good as possible [making the time interval as small as possible], so I wondered, could we make a 'bad' assay — one that could detect HIV as late as possible but still reliably detect HIV?"
To achieve this goal, scientists modified three elements — sample dilution, sample incubation time, and conjugate incubation time — of the present 3A11 assay (Abbott Laboratories, Abbott Park, IL) to produce the less sensitive assay.
In a large multi-population study, researchers were able to show the validity of the dual-testing algorithm. They stated, "The sensitive/less sensitive testing strategy provides accurate diagnosis of early HIV-1 infection, provides accurate estimates of HIV-1 incidence, can facilitate clinical studies of early HIV-1 infection, and provides information on HIV-1 infection duration for care planning."2
Since the study was published, researchers from the CDC have spent much time standardizing the testing strategy, says Janssen.
"It is a test that is simple in principle, and even the lab techniques are simple in principle," he notes. "Making the dilutions can be difficult."
The protocol has since been refined so the testing strategy may be reproduced easily. Several testing sites are working under an investigational new drug application with the U.S. Food and Drug Administration, says Janssen, and a number of researchers are using the dual-testing algorithm strategy to enroll patients in their studies of early HIV.
Scientists also are looking at the application of the STARHS technology in international testing situations, Janssen confirms. Further work is needed to refine the test for the various subtypes of HIV found in other countries.
Incidence still high
Results from applying the STARHS technology in high-risk settings were presented recently at the recent National HIV Prevention Conference in Atlanta, which was convened by the CDC and 17 other sponsoring organizations. The findings indicate that HIV incidence continues at high levels in the United States.3-6 The highest rates of infection in the four presentations were found among gay and bisexual men and people coinfected with other sexually transmitted diseases.7
"This new testing technique provides us with a snapshot of the epidemic's leading edge," says Janssen. "We can now better identify new epidemics while they are still emerging, and intervene before infection spreads more broadly."
References
1. Schwarcz S. A new HIV test to detect recent infections. FOCUS 1999; 14(3).
2. Janssen RS, Satten GA, Stramer SL, et al. New testing strategy to detect early HIV-1 infection for use in incidence estimates and for clinical and prevention purposes. JAMA 1998; 280:42-48.
3. McFarland W. HIV incidence among clients at anonymous sites in San Francisco. Presented at the National HIV Prevention Conference. Atlanta; Aug. 30, 1999.
4. Weinstock H. HIV sero-incidence among high risk heterosexuals and men who have sex with men in the U.S. using a dual EIA testing strategy. Presented at the National HIV Prevention Conference. Atlanta; Aug. 30, 1999.
5. Valleroy L. HIV incidence among young men who have sex with men in seven U.S. metropolitan areas. Presented at the National HIV Prevention Conference. Atlanta; Aug. 30, 1999.
6. Schwarcz-Kaplan S. Trends in HIV incidence among STD clients in the San Francisco Health Department — 1989-98. Presented at the National HIV Prevention Conference. Atlanta; Aug. 30, 1999.
7. National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention. New Data Show Decline in AIDS Deaths Slowing Down. Centers for Disease Control and Prevention, Atlanta; Aug. 30, 1999.
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