A study to evaluate immunodiagnostic tests for tuberculosis infection and determinants of TB infection in a population of health care workers in the Western Cape of South Africa

Background: Health care workers are at increased risk of acquiring latent tuberculosis infection (LTBI). The emergence of interferon - gamma release assays (IGRAs) for the diagnosis of LTBI, presents an opportunity for improved estimation of TB infection prevalence and incidence. Their utility in settings with high background prevalence TB and HIV infection is unknown. Major aims of the study were to: * Evaluate the prevalence and factors associated with TB infection using both tuberculin skin test (TST) and IGRA assays in a sample of health care workers. * Evaluate change in interval test response over one year to determine annual risk of infection and determinants associated with test conversion. Methods: Participants completed a questionnaire on occupational and environmental characteristics including a TB symptom screen and underwent chest radiograph and rapid HIV test. Three tests for latent TB infection were administered: TST, QuantiFERON - TB Gold In - Tube (QFT - GIT) and a T - SPOT.TB test. All tests were repeated one year later. Results: The prevalence of TB infection at baseline was 84%, 65% and 60% as measured by TST, QFT - GIT and T - SPOT.TB. There was only fair agreement between TST and IGRAs. HIV positive status was significantly associated with having a TST negative / T - SPOT.TB positive discordant test response (OR=4.72). TST had superior sensitivity than IGRAs for the diagnosis of LTBI. In primary level staff a positive TST outcome, was negatively associated with HIV positive status (OR=0.41). Long employment duration was positively associated with TST (OR=4.17) and QFT - GIT (OR= 2.42) positivity. Involvement in sputum collection (OR=3.25) and home - based care of TB patients (OR= 4.14) was associated with a positive IGRA test. The conversion rate for TST and IGRAs was 38% and 22%, respectively. Reversion rates ranged from 1 % - 16 % and was lowest for TST. Factors associated with conversion (for IGRAs) included employment sector, counselling of TB patients and a baseline positive TST. Conclusion: The annual rate of TB infection was very high pointing to occupational exposure as a contributory factor. TST had superior sensitivity than IGRAs for LTBI diagnosis but poor uptake on serial testing. IGRAs had excellent uptake but its clinical utility was negatively influenced by high rates of reversion.

Grantor dc:publisher.institution

Department of Public Health and Family Medicine

Year dc:date.issued

2015

Author dc:creator

• Adams, Shahieda

Advisors dc:contributor.advisor

• Dheda, Keertan
• Ehrlich, Rodney

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/15468

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/15468