USE OF POOLING AND OUTPATIENT LABORATORY SPECIMENS IN AN ANONYMOUS SEROPREVALENCE SURVEY OF HIV-INFECTION IN BRITISH-COLUMBIA, CANADA

Objective: To conduct an anonymous HIV seroprevalence survey to establ ish a baseline estimate;of HIV seroprevalence in a general population; to evaluate serum pooling and alternative testing strategies as cost- saving measures. Design: Prospective anonymous HIV seroprevalence stud y using outpatient laboratory specimens. Setting: Two large non-hospit al-associated outpatient chemistry testing laboratories in the major p opulation centers in British Columbia, Canada. Patients and sera: Left over sera received for chemistry screen testing in outpatient laborato ries were provided to the study after chemistry testing was completed. Those from patients aged <15 and greater than or equal to 55 years we re excluded. Methods: Patient identifiers were erased from samples. Se ra were pooled 10:1 and tested by viral lysate enzyme-linked immunosor bent assay (ELISA). Sera from HIV-positive pools were tested individua lly. All individual HIV-positive specimens were retested for verificat ion of positivity using a recombinant protein ELISA. Main outcome meas ures: HIV seroprevalence rates were stratified by sex, age group, and geographic area; and costs of pooling and alternative algorithm strate gy were compared with those of conventional methods. Results: A total of 80 238 sera were collected from 66 658 individuals (53% women, 47% men). Of these, 276 men (88.3 per 10000) and 24 women (6.8 per 10000) were HIV-seropositive. The highest rates were in those aged 30-34 year s, for both men and women. Using pooling and non-Western blot verifica tion saved US$2.07 per specimen, or 80% of the cost for conventional t esting. Conclusions: The anonymous outpatient laboratory setting is pr acticable to obtain a reasonable estimate of HIV seroprevalence rates in a general population. Such studies can be made cost-effective by po oling sera and using alternative confirmatory strategies.