Abstract
Background: Serum vitamin D (VitD) status is associated with active tuberculosis (TB) and TB infection conversion (TBIC).
Objectives: The objective of the present study was to quantify the risks of TB (latent, conversion, disease) in accordance with VitD
status and other variables among the contacts of pulmonary TB patients.
Methods: From 2009 to 2012, a cohort of the contacts of pulmonary TB patients was studied to rule out and prevent TB in Castellon
(Spain). The exams performed included a tuberculin skin test (TST), a QuantiFERON Gold in-tube test® (QFTGIT), blood and radiographic
tests, and an initial measurement of serum VitD status. Contacts who were initially without active TB were followed up
through 2015. Multinomial logistic regression (MLR) analyses were carried out.
Results: From a total of 572 contacts of pulmonary TB patients with VitD status measurement, 523 completed the follow-up (participation
rate 91.4%). Among them, five groups could be established: 3 new cases of pulmonary TB (0.6%), 27 cases of TBIC (5.2%),
116 cases of latent TB infection (LTBI) (22.2%), 125 uninfected TB contacts with only one TST or QFTGIT measurement (23.9%), and 252
uninfected TB contacts with two TST or QFTGIT measurements (48.2%). The comparison of these five groups revealed several significant
differences, including age, whether they were foreign-born, place of residence, social class, high exposure to an index case with
sputum acid-fast bacilli (AFB), and VitD status. The MLR analysis for all groups, with the group of uninfected TB contacts with two
TST or QFTGIT measurements as a reference, estimated that only two of these factors were significantly associated with TB in three
or more groups; these factors were VitD status and high exposure and a sputum AFB-positive index case. VitD status was a protector
against pulmonary TB with a relative risk (RR) of 0.86 (95% confidence interval [CI] 0.74 - 0.99) and against TBIC (R = 0.95; 95% CI 0.91
- 0.99), while it was not associated with LTBI (RR = 0.99; 95% CI 0.97-1.01). Only 34.0% of the contacts had sufficient VitD levels (≥ 30
ng/mL).
Conclusions: Our results suggest that a sufficient VitD level could be a protective factor against TBIC and active TB.