Updating HIV testing algorithms for today’s world

Dec. 1, 2010

WB and IFA confirmatory tests, however, are less sensitive in early HIV infection than some of the newer tests. Fourth-generation immunoassays became available in the U.S. in June 2010, and nucleic-acid amplification tests (NAATs) have been available for several years for detection of HIV RNA, which may be present during the so-called “window period” between infection and the development of detectable antibodies. Diagnosing illness during the window period — defined clinically as acute infection — enables more effective disease management and earlier counseling to help people change behaviors associated with disease transmission.

For the past several years, APHL has been involved in efforts to update HIV testing guidelines both in the U.S. and in resource-constrained nations with limited availability of laboratory testing. In April 2009, APHL and the CDC released a status report, describing a menu of proposed HIV testing algorithms that, upon further evaluation, might be used to augment or replace the algorithm currently used to detect HIV infection in the U.S. Earlier this year, the two organizations convened the 2010 HIV Diagnostics Conference, involving HIV test manufacturers; federal, state, and local health officials; Department of Defense officials; academicians; and public-health, clinical, and hospital laboratorians.

A major outcome of the 2010 conference was the proposal of a single laboratory algorithm for HIV testing. The proposed protocol uses a highly sensitive immunoassay as an initial test, ideally a fourth-generation antigen-antibody combination test. Specimens positive on the initial assay would be subjected to an antibody test with the ability to discriminate between HIV-1 and HIV-2. Specimens that test negative with the HIV-1/2 discriminatory assay or that yield inconclusive results would be subjected to a NAAT.

This proposed algorithm offers several advantages. It can 1) detect acute infection; 2) has a more rapid turnaround time than an algorithm employing a WB; 3) detects both HIV-1 and HIV-2 antibodies; 4) differentiates HIV-1 from HIV-2; and 5) eliminates WB testing, which is often indeterminate. APHL and CDC are continuing to collect supporting data to substantiate this proposed algorithm.

APHL, with CDC support, is also providing technical assistance to the Nigeria Federal Ministry of Health and CDC-Nigeria, which is developing and validating a standard for HIV testing that will be mandated for use in all Ministry of Health settings: hospitals, clinics, and HIV counseling and testing centers. Because most sub-Saharan African nations have a high prevalence of HIV infections, a parallel HIV testing algorithm is used to minimize false-negatives. Nigeria, however, has a relatively low HIV seroprevalence, estimated at 3.3% and, therefore, proposes to use a serial testing algorithm to minimize false positives. Nevertheless, with a population of approximately 150 million, Nigeria has the second largest HIV-positive population in sub-Saharan Africa, and the challenge of providing access to accurate and inexpensive HIV testing is not insignificant.

The proposed algorithm uses only rapid tests that can be stored without refrigeration, require little to no subjective interpretation, and provide same-day results at a cost of about $2 to $5 per test, compared to about $20 for an enzyme-linked immunosorbent assay. Phase I of the algorithm development — rapid HIV test kit evaluation in a controlled laboratory setting — is complete, and Phase II — pilot testing in non-controlled settings, with results compared to enzyme-linked immunosorbent assay and WB, is underway. Nationwide implementation of the new algorithm is expected to begin in 2011.

APHL’s work in both the U.S. and Africa reflects the critical need to fully exploit HIV test advances to support public-health efforts to curb HIV and to benefit high risk individuals around the world.

Nancy Maddox, MPH— writing on behalf of the Association of Public Health Laboratories — is co-founder of Maren Enterprises, a consulting firm specializing in technical and promotional writing in the field of public health.