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Open Access Research article

Low specificity of HIV-testing on sputum specimens kept at ambient temperatures for 4 to 7 days: a blinded comparison

Saidi M Egwaga1, Timothy M Chonde2, Mecky I Matee3, Sayoki G Mfinanga4, Prosper E Ngowi2, Fred Lwilla1 and Frank GJ Cobelens56*

Author Affiliations

1 National Tuberculosis and Leprosy Program, Dar-es-Salaam, Tanzania

2 Central Tuberculosis Reference Laboratory, Dar-es-Salaam, Tanzania

3 Muhimbili University College of Health Sciences, Dar-es-Salaam, Tanzania

4 National Institute for Medical Research, Muhimbili Medical Research Centre, Dar-es-Salaam, Tanzania

5 KNCV Tuberculosis Foundation, The Hague, The Netherlands

6 Center for Infection and Immunity Amsterdam, Academic Medical Center, Amsterdam, The Netherlands

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BMC Clinical Pathology 2007, 7:8  doi:10.1186/1472-6890-7-8

Published: 19 September 2007

Abstract

Background

HIV testing on sputum using the QraQuick HIV1/2® assay has high sensitivity and specificity, and holds promise for application in tuberculosis surveys. Its performance under conditions that may occur during surveys in resource-poor countries is however, unknown. We assessed, in a blinded comparison with HIV serum testing, the sensitivity and specificity of the OraQuick® assay for detecting HIV antibody in sputum specimens kept at ambient temperature for up to 7 days, with and without decontaminant.

Methods

Paired sputum and blood specimens from consecutively diagnosed smear-positive tuberculosis patients were tested with OraQuick® and 2 HIV-1/2 ELISA's. Sputum was tested within 24 hours of collection, split into 2 aliquots with and without addition of cetylpyridium chloride, and tested again after 4 and 7 days.

Results

Complete data was available for 377/435 (87%) enrolled patients; 132 (35%) tested HIV positive on serum. The sensitivity of the sputum test was 94.7% (95% CI 89.4–97.8) on day 1, 93.2% on day 4 and 92.9% on day 7. The specificity was 92.9% (95% CI 88.9–95.8) on day 1, and declined to 76.7% on day 4 (p < 0.001) and to 62.7% on day 7 (p < 0.001). Adding cetylpyridium chloride further decreased the specificity to 67.8% on day 4 (p = 0.04) and to 49.6% on day 7 (p = 0.004).

Conclusion

Transportation of sputum specimens at ambient temperatures for 4 days or more, and addition of decontaminant, strongly affect the specificity of the OraQuick® assay. Unless applied within one day, this assay is not suitable for estimation of HIV-prevalence among tuberculosis patients in survey settings.