Prevalence of abnormal radiological findings in health care workers with latent tuberculosis infection and correlations with T cell immune response

Abstract

Background: More than half of all health care workers (HCWs) in high TB-incidence, low and middle income countries are latently infected with tuberculosis (TB). We determined radiological lesions in a cohort of HCWs with latent TB infection (LTBI) in India, and determined their association with demographic, occupational and T-cell immune response variables.

Methodology: We obtained chest radiographs of HCWs who had undergone tuberculin skin test (TST) and QuantiFERON-TB Gold In Tube (QFT), an interferon-gamma release assay, in a previous cross-sectional study, and were diagnosed to have LTBI because they were positive by either TST or QFT, but had no evidence of clinical disease. Two observers independently interpreted these radiographs using a standardized data form and any discordance between them resolved by a third observer. The radiological diagnostic categories (normal, suggestive of inactive TB, and suggestive of active TB) were compared with results of TST, QFT assay, demographic, and occupational covariates.

Results: A total of 330 HCWs with positive TST or QFT underwent standard chest radiography. Of these 330, 113 radiographs (34.2%) were finally classified as normal, 206 (62.4%) had lesions suggestive of inactive TB, and 11 (3.4%) had features suggestive of active TB. The mean TST indurations and interferon-gamma levels in the HCWs in these three categories were not significantly different. None of the demographic or occupational covariates was associated with prevalence of inactive TB lesions on chest radiography.

Conclusion/significance: In a high TB incidence setting, nearly two-thirds of HCWs with latent TB infection had abnormal radiographic findings, and these findings had no clear correlation with T cell immune responses. Further studies are needed to verify these findings and to identify the causes and prognosis of radiologic abnormalities in health care workers.

Figure 1. Study flow chart and distribution of individuals according to their tuberculin skin test (TST) and QuantiFERON-TB Gold assay (QFT) results.

Figure 2. Distribution of tuberculin skin test indurations, and interferon gamma levels across different radiological categories.

With the individuals with a normal CXR as the reference, the mean TST indurations (mm) in the groups with calcified nodules alone, and other inactive lesions were not statistically significant (p values 0.98, and 0.34). TST induration was significantly higher in HCWs with radiological lesions suggestive of possible active TB (p=0.03), as compared to those with normal CXR. With the individuals with a normal CXR as the reference, the mean IFN-g values (IU/mL) in the groups with calcified nodules alone, other inactive lesions, and lesions suggestion of active TB were not statistically significantly (p values 0.34, 0.63 and 0.91 respectively)