Little is known about the frequency, subsequent outcomes and factors associated with indeterminate HIV rapid results. We assessed final HIV serological outcomes for individuals with rapid indeterminate test results and associated risk factors in Rakai, Uganda.
54,469 HIV rapid test results, defined by two parallel rapid tests, among 31,413 participants aged 15-49 years in the Rakai Community Cohort Study were assessed. 8361 participants were tested on two separate visits and 7354 had three time points tested. Each visit was approximately 18 months apart. Indeterminate results were defined as contradictory rapid test results or inconclusive concordant rapid test results. The final HIV status for each indeterminate observation was determined using previous HIV status information and additional testing, including PCR, ELISA and Western blot when necessary. Generalized estimating equations together with modified Poisson regression models with robust variance were used to assess prevalence ratios (PRs) of subsequent HIV serological outcomes and factors associated with indeterminate rapid test results.
The prevalence of HIV rapid test indeterminate results was 2.7% (1490/54,469). Of the 1,490 rapid indeterminate observations, 26% were eventually classified as HIV positive. The proportions of persons with rapid indeterminate results progressing to HIV rapid positive, negative, or still indeterminate at the subsequent visit were 19%, 40% and 41%, respectively. For individuals with two consecutive indeterminate results who had a third follow-up visit (67 individuals), 21% (14/67) tested negative, 9% (6/67) were positive and 70% (47/67) were still indeterminate.
Factors associated with higher risk of an indeterminate result were: women vs. men (adjPR 2.07, 95% CI 1.77,2.41); >44 vs. <20 years of age (adjPR 1.69, 95% CI 1.26,2.26); student vs. farmer (adjPR 0.62, 95%CI 0.46, 0.83); shopkeeper vs. farmer (adjPR 0.81, 95%CI 0.68, 0.96); ART vs. not (adjPR 1.29, 95% CI 1.10,1.51). In total, 4.4% of individuals on ART had indeterminate test results.
The frequency of indeterminate rapid results was low (<3%), and a quarter ultimately tested HIV positive. 41% of individuals with an indeterminate result had an indeterminate result on a follow-up visit and 0.64% of the population had continuous indeterminate results over a 3 year period.