Mean daily temperature (°C) and absolute humidity (g/m
) during the hazard and reference periods starting 7 days before and after the beginning of the hazard period. Values represent means of the observed cases of influenza (n = 66). For the logistic regression analyses the mean temperature and AH was calculated from the three preceding days (day-3 to 0) of the onset of an influenza infection and similarly for the reference periods 7 days before and after the infection. A maximum decline in temperature and AH was calculated as the largest change (maximum versus minimum) occurring in these parameters within the three day period (e.g. day −3 versus day −2, day −3 versus day −1, day −2 versus day −1 etc.) and similarly for the reference periods.