![[ Visit Client Website ]](images/banner.jpg)
BACKGROUND: Legionellosis is caused by the bacteria Legionella, found naturally in the environment, usually in water. Disease occurs when individuals inhale contaminated water vapor, and historically has been associated with exposures such as hot tubs, cooling towers, nebulizers, and decorative fountains. Incidence of legionellosis has been increasing in New Jersey (NJ) over the last decade. The majority of cases have no identified exposure, indicating that a broader common exposure may exist. Recently, researchers have hypothesized that the incidence of legionellosis may be associated with weather patterns, such as increased rainfall, humidity, heat, and cloud cover.
METHODS: Two study designs were used to evaluate associations of legionellosis and meteorological factors: time-series and case-crossover. Cases of legionellosis among NJ residents reported from 2003 through 2013 were geocoded to one of five climatic regions in NJ, based on home address. Cases in which patients were out of NJ during the entire incubation period (2 through 10 days prior to onset) were excluded. For the time-series, the number of cases per month in each region was matched with the average monthly temperature (daily minimum, maximum, and mean), precipitation, dew point, relative humidity, sea level pressure, wind speed (daily maximum and mean), gust, and visibility. Time-stratified case-crossover study design with bi-directional control sampling was employed to estimate increased risk of legionellosis with daily weather exposure data. Each case was matched to two controls by day of symptom onset. Daily lag exposures were also evaluated (Lag0-Lag15) Multivariate Poisson regression for time-series controlling for month, year, and region and multivariate conditional logistic regression for case-crossover estimated associations of temperature, rainfall, and relative humidity while controlling for other meteorological factors. Interquartile range (IQR) rate ratios were compared to estimate the effect of meteorological exposures and legionellosis.
RESULTS: Using time-series analysis, we determined the rate of legionellosis was 2.7 times greater (95% CI: 2.44-2.99) for each IQR increase of monthly dew point (IQR: 37.1°F). Increasing monthly averages of minimum daily temperature and relative humidity were strongly associated with legionellosis with IQR rate ratios of 2.57 (95% CI 2.34-2.83) and 2.48 (95% CI 2.25-2.73). In the case-crossover design relative humidity (OR=1.16, 95% CI 1.07-1.25) and sea level pressure (OR=0.89, 95% CI 0.85-0.93) were most strongly associated with legionellosis in multivariate models.
CONCLUSIONS: It is possible that meteorological factors, such as warm, humid weather with low barometric pressure, allow proliferation of Legionella in natural environments, increasing the rate of legionellosis.