Asthma mortality based on death certificates: A demographic survey in Kagawa, Japan

We aimed to determine the reasons for the high rate of asthma mortality in Kagawa Prefecture, Japan, by analyzing death certificates.

We analyzed the death certificates between 2009 and 2011 in a demographic survey. Of 1187 patients with documented disease names suggesting bronchial asthma, analysis was performed on 103 patients in whom the cause of death was classified as asthma based on ICD-10 Codes. The patients were then classified into the following 4 groups: asthma death, asthma-related death, non-asthma death, and indistinguishable death. Based on this classification, consistency between ICD-10-based asthma death and asthma/asthma-related deaths was examined for each age group as well as for the site of death.

Of 103 asthma deaths based on the ICD-10 classification, 30 (29%) were classified as asthma death, 44 (43%) as asthma-related death, 16 (16%) as non-asthma death, and 13 (13%) as indistinguishable death. Asthma death based on our classification correlated with that of ICD-10-based classification as a cause of death in patients younger than the median age (87 years), but correlation was not observed in patients aged older than 87 years. Deaths occurred outside the hospital in 45% of patients, and many ICD-10-based deaths reported at nursing homes and geriatric health care facilities were classified as non-asthma deaths in this survey.

Re-examination of the death certificate revealed that asthma deaths were reported incorrectly on the death certificates of elderly patients who died outside the hospital.