Affiliation: Gillings School of Global Public Health, Department of Epidemiology
Mycobacterium tuberculosis is the causative agent of pulmonary tuberculosis (TB) disease, but environmental factors may influence disease susceptibility and or progression from infection to disease. Ecologic analyses, including a preliminary study conducted, suggest a possible link between active TB and ambient air pollution. Animal models demonstrate that air pollution is associated with a reduction in cytokines that normally prevent latent TB infection (LTBI) from progressing into clinical disease. The primary objective of this investigation was to evaluate the association between ambient air pollution (as measured by SO2, NO2, CO, O3, PM2.5 and PM10) and incident pulmonary TB (PTB). An additional aim was to determine whether cigarette smoking is a risk factor for PTB disease in this population, and whether smoking influences the association between air pollution and increased risk of developing PTB. To address these aims a case-control study nested among members of Kaiser Permanente Northern California (KPNC) was undertaken. Using electronic clinical databases (ECD), incident cases of PTB diagnosed among adults between the years 1996-2010 were selected, and controls without a history of PTB matched to the cases on age, gender, and race/ethnicity. Cigarette smoking, current and historical residential addresses, and other covariates of interest were abstracted from the ECD. To estimate individual-level pollutant exposure geocoded addresses were linked to inverse distance weighted surfaces of average monthly pollutant concentrations, produced by the California Air Resources Board. Logistic regression models were used to evaluate the relationship between individual air pollutant and incident PTB, stratifying on history of cigarette smoking. These results are the first from an analytic epidemiologic investigation undertaken to formally evaluate the hypothesis that individual-level estimates of air pollution concentrations are associated with an increased risk of incident PTB. Considering the high air pollution levels and increasing TB rates internationally, their potential association warrants study.