Replacing clinic-based tests with home-use tests may increase HIV prevalence among Seattle men who have sex with men: evidence from a mathematical model

Abstract

Background: Home-use tests have potential to increase HIV testing but may increase the rate of false-negative tests and decrease linkage to HIV care. We sought to estimate the impact of replacing clinic-based testing with home-use tests on HIV prevalence among men who have sex with men (MSM) in Seattle, Washington.

Methods: We adapted a deterministic, continuous-time model of HIV transmission dynamics parameterized using a 2003 random digit dial study of Seattle MSM. Test performance was based on the OraQuick In-Home HIV Test (OraSure Technologies, Inc, Bethlehem, PA) for home-use tests and, on an average, of antigen-antibody combination assays and nucleic acid amplification tests for clinic-based testing.

Results: Based on observed levels of clinic-based testing, our baseline model predicted an equilibrium HIV prevalence of 18.6%. If all men replaced clinic-based testing with home-use tests, prevalence increased to 27.5% if home-use testing did not impact testing frequency and to 22.4% if home-use testing increased testing frequency 3-fold. Regardless of how much home-use testing increased testing frequency, any replacement of clinic-based testing with home-use testing increased prevalence. These increases in HIV prevalence were mostly caused by the relatively long window period of the currently approved test. If the window period of a home-use test were 2 months instead of 3 months, prevalence would decrease if all MSM replaced clinic-based testing with home-use tests and tested more than 2.6 times more frequently.

Conclusions: Our model suggests that if home-use HIV tests replace supplement clinic-based testing, HIV prevalence may increase among Seattle MSM, even if home-use tests result in increased testing.

Figure 1

Flowchart of a mathematical model of home-use testing among MSM in Seattle. Compartments are defined by anal sexual activity level A (none; 1, low; 2, high), true HIV serostatus, and HIV testing site C (0 [home-use tests] vs. 1 [clinic-based tests]). HIV-infected men are further subdivided by disease stage, detectability by clinic-based or home-use tests, and (if diagnosed) by ART use.

Figure 2

Equilibrium HIV prevalence for various proportions of home-use testing (vs. clinic-based testing) in the population at varying testing frequencies among those testing at home. As the proportion of MSM who test at home instead of in a clinic increases, equilibrium HIV prevalence rises. If home-use tests replace clinic-based testing completely, prevalence increases from 18.6% to 27.5%, assuming no changes in testing frequency. Increasing testing frequency among men testing at home reduces this effect on prevalence but does not reverse it completely. Note: a 3-fold increase in testing frequency results in an average of 3 and 6 tests per year among low- and high-activity men, respectively.

Figure 3

Equilibrium HIV prevalence at varying testing frequencies and home-use test window periods when all testing occurs at home. The gray line represents the equilibrium prevalence in the baseline scenario of 100% clinic-based testing: 18.6%. Average testing frequency in the figure ranges from 1 to 6 tests per year among low-activity men and 2 to 12 tests per year among high-activity men. With a 90-day window period, if clinic-based testing is replaced completely by home-use tests, equilibrium prevalence is greater than 18.6% regardless of home much home-use tests increase testing frequency. If the window period of a home-use test were 60, 42, 28, or 15 days, equilibrium prevalence would equal 18.6% if home-use tests increased testing frequency by 2.6, 1.6, 1.20, or 1.1 times, respectively.

Figure 4

Increases in equilibrium HIV prevalence as a result of replacing clinic-based testing with home-use tests varying the rate of HIV testing and the window period of clinic-based tests. The impact of replacing clinic-based testing with home-use tests on equilibrium HIV prevalence depends on the average testing frequency among MSM as well as the window period of the tests. The more frequently MSM test for HIV infection and the shorter the window period of clinic-based tests, the greater the increase in HIV prevalence when clinic-based testing is replaced with home-use tests. For example, in the model scenario representing Seattle, low-activity men average 1 test per year, high-activity men average 2, and the window period of clinic-based testing is 15 days. Replacing clinic-based testing with home-use tests in this scenario results in an 8.9% increase in equilibrium HIV prevalence (18.6%–27.5%). On the other hand, in a setting where low- and high-activity MSM average 1 test every 2 years and clinic-based tests have a 42-day window period, replacing clinic-based testing with home-use tests results in only a 1.0% increase in prevalence (33.6%–34.6%).