Ambient sulfur dioxide levels associated with reduced risk of initial outpatient visits for tuberculosis: A population based time series analysis

Abstract

Background: Recent biochemical studies suggest that exogenous sulfur dioxide (SO₂) at low concentrations may have been beneficial in inhibiting mycobacteria tuberculosis (TB) growth. However, there is a dearth of population-based studies.

Objectives: To examine the association of ambient SO₂ levels and initial TB outpatient visits.

Methods: In Ningbo, China, we collected all daily initial outpatient visits for TB and routinely air pollution monitoring data between January 2009 and December 2013. A time-series study was conducted by using generalized additive regression (GAM) with log-linear Poisson models to estimate the associations between daily initial TB outpatient visits and daily average concentration of SO_2. Other traffic-related co-pollutants were adjusted. Sensitivity analyses were conducted to examine the relationship when 1% extreme SO₂ concentrations excluded or if related to the early onsets of TB symptoms.

Results: SO₂ concentrations in Ningbo were low with a daily average of 25 μg/m³ (i.e. 0.0089 ppm). Negative associations were identified between ambient SO₂ concentrations and daily initial TB outpatient visits. A 10 μg/m³ increase in SO₂ at lag₃ and lag_0-3 days were associated with -2.0% (95%CI, -3.2, -0.8) and -4.6% (95%CI, -6.8, -2.4) changes, respectively, in initial TB outpatient visits according to single-pollutant models. The negative association became stronger when nitrogen dioxide (NO₂) or particulate matter with aerodynamic diameter less than 10 μm (PM₁₀) was adjusted in two-pollutant models. This association was higher in males vs. females and in middle-aged adults vs. the elderly. We found a stronger negative association between SO₂ concentration and the initial symptom occurrence.

Conclusion: Short-term exposure to ambient SO₂ was associated with reduced risk of initial TB outpatient visits, suggesting acute protective effects of low-level ambient SO₂ exposure on bacteria-induced pulmonary infections.

Keywords: China; Sulfur dioxide; Time-series study; Tuberculosis.