Lower air temperature is associated with higher ambulance transports in Sakata area, Yamagata prefecture, Japan

To investigate the link between low air temperature and ambulance transports in Japan. Data on climate parameters i.e. air temperature, humidity and daylight hours in Sakata area, Yamagata prefecture, Japan, which is northern part (Tohoku) in Japan, was obtained from Japan Meteorological Agency. Monthly data on ambulance transports due to acute disease from 2005 to 2011 was also directly obtained from Sakata area official website, Japan. The relations between air temperature and ambulance transports were evaluated by ecological study. Ambulance transports per day were 10.1 ± 1.0 and mean air temperature was 13.0 ± 8.4 (°C). Ambulance transports per day were weakly and negatively correlated with mean air temperature, mean of the highest air temperature, mean of the lowest air temperature, the highest air temperature and daylight hours. It was also weakly and positively correlated with mean humidity. However, the relation between ambulance transports and mean air temperature was well estimated by quadratic curve (r = 0.633, p < 0.0001). Lower air temperature was closely associated with higher ambulance transports, as well as higher air temperature was associated with higher ambulance transports in Sakata area, Japan.