“Risk factors for tuberculosis among close IGRA-negative contacts of persons with infectious tuberculosis in Singapore”

Abstract

BackgroundContacts of infectious TB cases testing positive on Interferon-Gamma Release Assay (IGRA) are followed up to exclude active disease. However, factors that predispose IGRA-negative contacts to TB could improve screening and follow-up strategies in a medium TB burden country like Singapore. MethodsWe conducted a retrospective study of IGRA-negative contacts aged ≥2 years identified during contact investigation between January 2014 and December 2022. We examined the risk factors associated with developing active TB among contacts previously testing IGRA-negative, using univariate and multivariable logistic regression and odds ratios (OR) with 95% confidence intervals (CI). ResultsOf 60,377 IGRA-negative contacts, 150 developed TB disease and half were notified within 23 months of index diagnosis. IGRA-negative contacts of a smear-positive index were more likely to develop TB. Independent risk factors for TB were being over 50, Malay, having Diabetes or End-Stage Renal Failure, a “family” relationship with the index or exposure in a dormitory or nursing home. ConclusionCertain risk factors could help optimize follow-up strategies and preventive treatment in IGRA-negative individuals. The incidence of TB in this group was 150/100,000 population, substantially higher than in the community, with a median 92 weeks to develop disease. Findings suggest that follow-up be extended to 24 months for contacts with these risk factors.