Winter season temperature drops and sulfur dioxide levels affect on exacerbation of refractory asthma in South Korea: a time-trend controlled case-crossover study using soonchunhyang asthma cohort data.

OBJECTIVE: According to the American Thoracic Society, approximately 5% of all asthmatics have refractory asthma (RA); these patients fail to recover lost lung function even after long-term treatment with high doses of medications.
METHODS: Using a time-trend controlled case-crossover study design, we calculated odds ratios to evaluate whether exposure to ambient air pollutants and certain meteorological conditions on the day of admission (Lag 0) and up to 3 days before admission (Lag1 through Lag 3) were associated with acute RA exacerbation. Results were obtained after controlling for the effects of seasonality, smoking, and allergen sensitivity; we stratified our data into four seasons with respect to the median temperature of each month and further stratified them according to self-reported smoking status and skin-prick test results.
RESULTS: In our study, RA patients (n = 82), living in metropolitan city of Seoul and Kyunggi Province, accounted for 3.7% of all asthmatics (n = 2298) registered in our asthma cohort between 2005 and 2009. In winter, a 1°C decrease in ambient temperature and a 1 ppb increase in sulfur dioxide concentration on the day of Lag 1 were associated with 14.8% (95% confidence interval [CI]: 0.9-26.7) and 19.7% (95% CI: 3.3-38.7) increases in the risk of RA exacerbation among nonsmokers, respectively. Similar associations were obtained on the day of Lag 2. The association remained unchanged after excluding patients sensitive to Dermatophagoides farinae and Dermatophagoides pteronyssinus.
CONCLUSIONS: Exposure to temperature drops and increased sulfur dioxide concentrations are positively associated with the occurrence of acute RA exacerbation during winter with 1 or 2 day lags.