BackgroundIn Japan, the demand for emergency transportation for people with heat-related illness has recently increased. The purpose of this study was to investigate the relationship between incidents of heat-related illness and the daily maximum temperature.

MethodsThe daily maximum temperatures in Japan's 11 districts over the past 10 years were classified into four categories, with cutoff points at the 50, 75, 95, and higher than 95percentiles. We then conducted a logistic regression analysis of emergency transportation demand in each temperature category by age group, using the 50percentile as the reference category for each area.

ResultsThere were 42,931 cases of emergency transportation due to heat-related diseases during the study period. Classified by age, 12.5%, 43.4%, and 44.1% of cases involved children, adults, and elderly people, respectively. The analysis showed that the number of cases of emergency transportation for people with heat-related diseases (per 100,000 people; corresponding to a 1.0°C increase in the daily maximum temperature) was 0.016-0.106 among children (24.9-169.9 children required emergency transportation for heat-related diseases), from 0.013 to 0.059 among adults (19.8-98.2 adults required emergency transportation), and from 0.045 to 0.159 among elderly persons (30.0-145.4 elderly people required emergency transportation). The risk was highest for elderly persons, followed by children and finally adults. Cases of emergency transportation due to heat-related illness increased by 2.4-8.9 times when the daily maximum temperature was approximately 1.5°C above the mean daily maximum temperature. In fact, the daily maximum temperature had a larger effect than the daily relative humidity level on emergency transportation for people with heat-related diseases.

ConclusionPublic health organizations and health-care services should support elderly people and children, two high-risk groups for heat-related diseases.