Exposure to second-hand smoke and the risk of tuberculosis in children and adults: A systematic review and meta-analysis of 18 observational studies
Abstract
Background
According to WHO Global
Health Estimates, tuberculosis (TB) is among the top ten causes
of global mortality and ranks second after cardiovascular
disease in most high-burden regions. In this systematic review
and meta-analysis, we investigated the role of second-hand smoke
(SHS) exposure as a risk factor for TB among children and
adults.
Methods and Findings
We performed a
systematic literature search of PubMed, Embase, Scopus, Web of
Science, and Google Scholar up to August 31, 2014. Our a priori
inclusion criteria encompassed only original studies where
latent TB infection (LTBI) and active TB disease were diagnosed
microbiologically, clinically, histologically, or
radiologically. Effect estimates were pooled using fixed- and
random-effects models. We identified 18 eligible studies, with
30,757 children and 44,432 adult non-smokers, containing SHS
exposure and TB outcome data for inclusion in the meta-analysis.
Twelve studies assessed children and eight studies assessed
adult non-smokers; two studies assessed both populations.
Summary relative risk (RR) of LTBI associated with SHS exposure
in children was similar to the overall effect size, with high
heterogeneity (pooled RR 1.64, 95% CI 1.00–2.83). Children
showed a more than 3-fold increased risk of SHS-associated
active TB (pooled RR 3.41, 95% CI 1.81–6.45), which was
higher than the risk in adults exposed to SHS (summary RR 1.32,
95% CI 1.04–1.68). Positive and significant
exposure–response relationships were observed among
children under 5 y (RR 5.88, 95% CI 2.09–16.54), children
exposed to SHS through any parent (RR 4.20, 95% CI
1.92–9.20), and children living under the most crowded
household conditions (RR 5.53, 95% CI 2.36–12.98).
Associations for LTBI and active TB disease remained significant
after adjustment for age, biomass fuel (BMF) use, and presence
of a TB patient in the household, although the meta-analysis was
limited to a subset of studies that adjusted for these
variables. There was a loss of association with increased risk
of LTBI (but not active TB) after adjustment for socioeconomic
status (SES) and study quality. The major limitation of this
analysis is the high heterogeneity in outcomes among studies of
pediatric cases of LTBI and TB disease.
Conclusions
We found that SHS
exposure is associated with an increase in the relative risk of
LTBI and active TB after controlling for age, BMF use, and
contact with a TB patient, and there was no significant
association of SHS exposure with LTBI after adjustment for SES
and study quality. Given the high heterogeneity among the
primary studies, our analysis may not show sufficient evidence
to confirm an association. In addition, considering that the TB
burden is highest in countries with increasing SHS exposure, it
is important to confirm these results with higher quality
studies. Research in this area may have important implications
for TB and tobacco control programs, especially for children in
settings with high SHS exposure and TB burden.
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Source:
PLOS Medicine
