Vitamin D status and latent tuberculosis infection: conversion in nursing homes, Spain.

OBJECTIVE

To examine the potential association between vitamin D (VitD) deficiency and latent tuberculosis infection (LTBI) and its effect on TB infection conversion (TBIC) incidence.MATERIAL AND

METHODS

We carried out a cross-sectional and prospective cohort study of nine pulmonary TB cases that occurred in 2015-2016 in five nursing homes and one mental disability institution in Castellon, Spain. QuantiFERON®-TB Gold and the tuberculin skin test were used to detect LTBI and TBIC, respectively. Serum 25-hydroxyvitamin D was measured using chemiluminescence immunoassay. Poisson regression and inverse probability weighting were used for statistical analyses.

RESULTS

The study included 448 residents, 341 staff members with 48 relatives of TB cases (participation rate 82%): of these, respectively 122 (27.2%), 37 (10.9%) and 7 (14.6%) were LTBI-positive; and respectively 22 (7.7%), 10 (3.8%) and 1 (3.7%) were TBIC-positive. LTBI was not associated with VitD status. Severe VitD deficiency (SVDD; defined as VitD level < 10 ng/ml), found in 45.1% of residents, as well as VitD levels of <30 ng/ml (aRR 10.41 95% CI 1.48-73.26), were associated with increased TBIC risk (adjusted relative risk [aRR] 12.1, 95% CI 1.51-97.10), suggesting SVDD as a threshold effect.

CONCLUSION

Severe VitD deficiency is a TBIC risk factor.