Adjusted incidence rate ratios for Gram-positive and Gram-negative pathogens by temperature in the month prior to isolation. As reference we defined temperatures in the month prior to isolation <5°C.

Abbreviations: °C, degree Celsius; IRR, incidence rate ratio; CI, confidence interval; GP, Gram-positive pathogens; GN, Gram-negative pathogens; CoNS, coagulase negative Staphylococci.
* p-value, chi-square test with 4 degree of freedom (type III test); ** p-value, chi-square test with 1 degree of freedom (type III test);.
NOTE: Adjusted incidence rate ratios were calculated using generalized estimating equations models using negative binomial distribution and logarithmic transformed patient days as offset parameter; 5965 monthly data sets of 73 different ICUs, January 2001 to December 2012. The adjusted models accounts for cluster effects within an ICU and for significant confounding parameters from the first model building step:
a, autoregressive factor AR(1) number pathogens in the previous month;
b, linear time trend;
c, quadratic time trend;
d, cubic time trend;
e, ICU is located in a university hospital;
f, hospital size > = 1000 beds;
g, type of ICU medical;
h, type of ICU surgical.