Weather patterns and Legionnaires' disease: a meteorological study.

This study examined the impact of meteorological conditions on sporadic, community-acquired cases of Legionnaires' disease in England and Wales (2003-2006), with reference to the 2006 increase in cases. A case-crossover methodology compared each case with self-controlled data using a conditional logistic regression analysis. Effect modification by quarter and year was explored. In total, 674 cases were entered into the dataset and two meteorological variables were selected for study based on preliminary analyses: relative humidity during a case's incubation period, and temperature during the 10-14 weeks preceding onset. For the quarter July-September there was strong evidence to suggest a year, humidity and temperature interaction (Wald chi2=30.59, 3 d.f., P<0.0001). These findings have implications for future case numbers and resource requirements.