There is controversy regarding the potential influence of vitamin D deficiency, exposure to environmental tobacco smoke, BCG vaccination, season and body habitus on susceptibility to Mycobacterium tuberculosis (MTB) infection.
We conducted a cross-sectional analysis to identify determinants of a positive QuantiFERON®-TB Gold (QFT) assay result in children aged 6-13 years attending 18 schools in Ulaanbaatar, Mongolia. Data relating to potential risk factors for MTB infection were collected by questionnaire, physical examination and determination of serum 25-hydroxyvitamin D (25[OH]D) concentrations. Risk ratios were calculated using generalized estimating equations with adjustment for potential confounders, and population attributable fractions (PAFs) were calculated for modifiable risk factors identified.
946/9,810 (9.6%) participants had a positive QFT result. QFT-positivity was independently associated with household exposure to pulmonary TB (adjusted risk ratio [aRR] 4.75, 95% CI 4.13-5.46, P<0.001; PAF 13.1%, 95% CI 11.1%-15.0%), vitamin D deficiency (aRR 1.23, 95% CI 1.08-1.40, P=0.002; PAF 5.7%, 1.9%-9.3%), exposure to environmental tobacco smoke (one indoor smoker, aRR 1.19, 95% CI 1.04-1.35; two or more indoor smokers, aRR 1.30, 95% CI 1.02-1.64; P for trend, 0.006; PAF 7.2%, 95% CI 2.2%-12.0%) and increasing age (aRR per additional year 1.14, 95% CI 1.10-1.19, P<0.001). No statistically significant independent association was seen for presence of a BCG scar, season of sampling or body mass index.
Our findings underline the importance of contact tracing in TB-exposed households as a strategy to identify MTB-infected children. Vitamin D deficiency and exposure to environmental tobacco smoke may be modifiable risk factors for MTB infection.