Feasibility of pooling sera for HIV-1 viral RNA to diagnose acute primary HIV-1 infection and estimate HIV incidence

Objective: To develop a pooling method for detection of viral RNA for diagn osis of acute HIV infection and estimation of HIV-1 incidence. Methods: Sera from 700 consecutive seronegative patients attending sexually transmitted disease clinics in Pune, India, were screened individually for p24 antigen, and pooled into seven pools of 100 for detection of HIV-1 RNA by reverse transcriptase-polymerase chain reaction. HIV-1 incidence was ca lculated by the traditional cohort method, the p24 antigen method, and a mu ltistage pooling method in which RNA-positive pools were re-analyzed in sma ller pools. Results: Sera from 700 individuals were grouped into seven pools of 100, of which four were positive. These four positive pools were subdivided into e ight pools of 50, of which seven were positive. The seven positive pools we re subdivided into 35 pools of 10, of which 10 were positive. Based on the 10 RNA-positive pools, the point estimate of HIV-1 incidence was 19.9% per year [95% confidence interval (CI), 7.3-31.8%]. Of the 700 samples analyzed for p24 antigen, eight were positive, resulting in a point estimate of inc idence of 18.5%/year (8.0-36.5%). In contrast, the incidence rate based on the traditional cohort method of follow-up was lower at 9.4%/year (4.8-16.4 %) due to a low follow-up rate. Testing of individual samples from the 10 R NA-positive pools identified 10 individuals with acute primary HIV-1. Conclusion: The multistage pooling method for detection of HIV-1 RNA was mo re sensitive than the p24 antigen method, and was five-fold less expensive than the p24 antigen assays. Pooling samples for RNA detection was effectiv e in estimating current incidence rates with cost savings that would be pra ctical for use in developing countries. (C) 2000 Lippincott Williams & Wilk ins.