Mortality statistics of the heat stroke in Japan: What statistical category should be used?

Abstract

The vital statistics of Japan do not include a category for mortality statistics using the term “heat stroke.” “Exogenous causes of injury and death” included the items “excessive heat (E900)” until 1994 along with “exposure to excessive nature heat (X30)” and “exposure to excessive heat of man-made origin (W92)” from 1995. The mortality counts of heat stroke is thought to be the mortality counts due to heat among these exogenous causes. According to the press release materials of the Ministry of Health, Labor and Welfare (MHLW), the mortality counts due to “exposure to excessive natural heat (X30)” should be the mortality counts of heat stroke. However, the “influence of exogenous causes of injury, intoxication, and others” included the subcategories “effects of heat (N992)” and “effects of heat and light (992)” until 1994 along with the “effects of heat and light (T67)” from 1995, which describes the specific symptoms of heat exhaustion such as heat stroke and sunstroke. Consequently, we believe the counts of T67, as the nature of injuries, is equivalent to the mortality counts of heat stroke. This study compared the mortality counts related to heat stroke regarding these statistical categories. There was no significant difference in the mortality counts between statistical categories until 1994. From 1995 to 2017, T67 was higher than X30, such that adding X30 to W92 made the difference between T67 and X30+W92 smaller. The possible cause for this is that E900 as a code of exogenous causes was divided into X30 and W92 from 1995. In the case of the mortality counts due to heat, we believe it is more appropriate to use the mortality counts in terms of the nature of injuries, rather than using the mortality counts due to excessive heat in nature (classification by causes). It is assumed that the mortality counts due to the “effects of heat and light (T67)” indicates the mortality counts of heat stroke in Japan.