OPTIMAL HIV TESTING BY RISK GROUP

Purpose: The CDC currently recommends one-time and annual HIV testing regimens for low-risk and high-risk individuals respectively. Since these recommendations were released in 2006, early initiation of highly active antiretroviral therapy (HAART) has become more common.  In light of these developments we re-analyze the optimal HIV testing regimen.

Method: We build a simple mathematical model to find the optimal testing frequency for various risk groups, using annual incidence rates as proxies for risk. We focus on high-risk (1% annual incidence), moderate-risk (0.1% annual incidence) and low-risk (0.01% annual incidence) individuals. The key parameter in our model is the incremental net monetary loss (INML) of delaying detection of an HIV infection by one year.  This parameter incorporates both monetary and health care costs.  We calculate the optimal testing frequency for three values for INML, $4,000, $1000, and $150.  We estimate an INML of $4,000 from a scenario of early HAART initiation and consider an INML of $1000 to be a more conservative value.

Result: With an INML of $4,000, the optimal time between tests is 4 years for low-risk groups, 1.2 years for moderate-risk groups, and 0.4 years for high-risk groups.  For an INML of $1,000, the optimal time between tests is 8 years, 2.4 years, and 0.8 years for low, moderate, and high-risk groups.  The current CDC guidelines are close to the frequencies that would be optimal with an INML equal to $150, an implausibly low value.  For an INML of $150, the optimal time between tests is 20 years for low-risk groups and 2 years for high-risk groups.

Conclusion: With a reasonable INML, our model suggests that HIV testing for low-risk individuals should be more frequent than the one-time testing currently recommended by the CDC.