Abstract
BackgroundWe investigated the relationship between average monthly temperature and the most common clinical pathogens causing infections in intensive care patients.MethodsA prospective unit-based study in 73 German intensive care units located in 41 different hospitals and 31 different cities with total 188,949 pathogen isolates (102,377 Gram-positives and 86,572 Gram-negatives) from 2001 to 2012. We estimated the relationship between the number of clinical pathogens per month and the average temperature in the month of isolation and in the month prior to isolation while adjusting for confounders and long-term trends using time series analysis. Adjusted incidence rate ratios for temperature parameters were estimated based on generalized estimating equation models which account for clustering effects.ResultsThe incidence density of Gram-negative pathogens was 15% (IRR 1.15, 95%CI 1.10–1.21) higher at temperatures ≥20°C than at temperatures below 5°C. E. cloacae occurred 43% (IRR = 1.43; 95%CI 1.31–1.56) more frequently at high temperatures, A. baumannii 37% (IRR = 1.37; 95%CI 1.11–1.69), S. maltophilia 32% (IRR = 1.32; 95%CI 1.12–1.57), K. pneumoniae 26% (IRR = 1.26; 95%CI 1.13–1.39), Citrobacter spp. 19% (IRR = 1.19; 95%CI 0.99–1.44) and coagulase-negative staphylococci 13% (IRR = 1.13; 95%CI 1.04–1.22). By contrast, S. pneumoniae 35% (IRR = 0.65; 95%CI 0.50–0.84) less frequently isolated at high temperatures. For each 5°C increase, we observed a 3% (IRR = 1.03; 95%CI 1.02–1.04) increase of Gram-negative pathogens. This increase was highest for A. baumannii with 8% (IRR = 1.08; 95%CI 1.05–1.12) followed by K. pneumoniae, Citrobacter spp. and E. cloacae with 7%.ConclusionClinical pathogens vary by incidence density with temperature. Significant higher incidence densities of Gram-negative pathogens were observed during summer whereas S. pneumoniae peaked in winter. There is increasing evidence that different seasonality due to physiologic changes underlies host susceptibility to different bacterial pathogens. Even if the underlying mechanisms are not yet clear, the temperature-dependent seasonality of pathogens has implications for infection control and study design.
Highlights
Seasonality is characteristic of many infectious diseases and has been recognized since Hippocrates who began his first book Epidemics with the description of the weather [1]
The time series of the incidence rates for the different Grampositive and Gram-negative pathogens in 73 German intensive care units (ICU) and mean monthly temperature in Germany are depicted in figure 1 and figure 2
There was an 8% increase for A. baumannii (IRR = 1.08; 95%confidence intervals (CI) 1.05–1.12), followed by K. pneumoniae, Citrobacter spp. and E. cloacae with 7%
Summary
Seasonality is characteristic of many infectious diseases and has been recognized since Hippocrates who began his first book Epidemics with the description of the weather [1]. He wrote in 400 BC: ‘‘Whoever wishes to investigate medicine properly should proceed : in the first place to consider the seasons of the year...’’. Data on summer peaks in the incidences of other Gram-negative bacterial infections among hospitalized patients have only recently been published [6,7,8]. The authors of the study by the University of Maryland reported that incidence rates for E. coli were 12 percent higher in summer than in winter. We investigated the relationship between average monthly temperature and the most common clinical pathogens causing infections in intensive care patients
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