Seasonal variation in the acute presentation of urinary calculi over 8 years in Auckland, New Zealand

OBJECTIVE To determine the incidence of acute presentation of urinary calculi (UC) in Auckland, New Zealand, during the period 1999-2007, and whether there was any significant seasonal variation. PATIENTS AND METHODS The details of all UC within the population presenting acutely to public hospitals in Auckland between 1999 and 2007 were collected using clinical coding searches International Classification of Disease 10th revision (Australian Modification) N132 and N20. Climatic variables for the Auckland region were obtained from the National Institute of Water and Atmospheric Research, New Zealand. The mean atmospheric temperature, hours of sunshine and humidity data were calculated monthly for this period. RESULTS During the study there were 7668 acute presentations of UC in the Auckland region. A Poisson regression model showed that the number of presentations was significantly related to temperature (P < 0.001) and hours of sunshine (P = 0.004) but not humidity (P = 0.14). For each degree increase in temperature the number of presentations increased by 2.8% (95% confidence interval 1.3-4.3%). For each 1-h increase in sunshine, the number of presentations increased by 0.2% (0.06-0.33)%. CONCLUSION The acute presentation of UC in Auckland, New Zealand, varies significantly with temperature and hours of sunshine. Humidity was not a significant factor.