Evolution of mortality associated with heat-sensitive diseases in Japan during the COVID-19 pandemic

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In a recent study published in PLOS ONEresearchers assessed the impact of the coronavirus disease 2019 (COVID-19) pandemic on mortality from temperature-sensitive illness.

Study: Impact of the COVID-19 pandemic on the evolution of mortality from temperature-sensitive cardiovascular and respiratory diseases in Japan. Image Credit: max.ku/Shutterstock

Cardiovascular and respiratory diseases caused 345,476 and 172,727 deaths respectively during the COVID-19 pandemic in 2020. Compared to 2019 (pre-COVID-19), this represented a considerable decrease of 5,029 and 20,507, respectively. This indicates that examining changes in the number of cardiovascular and respiratory deaths caused by behavioral changes will be crucial in researching a variety of issues, including climate change, public health, and population aging.

About the study

In the present study, researchers assessed variations in temperature-sensitive disease mortality during the COVID-19 pandemic in Japan.

The three largest cities that were the subject of this study were the city of Sapporo (Sapporo), the city of Osaka (Osaka) and the 23 wards of Tokyo (Tokyo), which have a population of 1.97 million , 2.75 million and 9.71 million, respectively, in 2021. These teams were rated because they presented different climates. For example, in August, average ambient temperatures were 22.3°C in Sapporo, 29°C in Osaka, and 26.9°C in Tokyo, while average temperatures in December were 0.9°C in Sapporo , 17.1°C in Osaka and 15.8°C in Tokyo.

The monthly death toll for each cause of death is made available on the Japanese government’s “e-Stat” portal website. Due to statistical reports produced by the Japanese Ministry of Health, Labor and Welfare (MHLW), the figures were very reliable. Heart failure (HF), intracerebral hemorrhage (ICH), cerebral infarction (IC), respiratory diseases (Resp), cardiac arrhythmia and conduction disorders (CACD) and ischemic heart disease (IHD) ) were the seven diseases examined in this study. The age-adjusted mortality rate (TMadj.) was applied to the population by age group to take into account annual variations and differences between cities.

Available data collected and provided by the Japan Meteorological Agency (JMA) served as the source for the Monthly Mean Temperature (MMT). The Automated Meteorological Data Acquisition System (AMeDAS), a network of many meteorological stations, was installed by the JMA throughout Japan. For the analysis, the corresponding AMeDAS in Sapporo City, Osaka City and Ota Ward in Tokyo were selected. The team estimated the outside air temperature to be around 1.5m above the ground.

Additionally, the duration of the COVID-19 pandemic was considered to be from March to December 2020, and the months between 2010 and 2019 were compared to those of the pre-pandemic era.

Results

For CACD, CI, HF, IHD, ICH and Resp, the MRadj. increased steadily in winter and decreased in summer from January 2019 to December 2020. Numerous studies have documented an increase in respiratory and cardiovascular mortality in the elderly during winter. In March 2020, COVID-19 began to spread in Japan. The overlap between the period of decline and the period of spread of COVID-19 seems to be a coincidence since the reduction of the MRadj. between spring and summer was observed in 2020 as well as in the pre-COVID-19 period.

With a decline in annual MMT in all cities, MRadj. increased with statistically significant associations for May IHD in Osaka and Sapporo, May CI in Osaka and Tokyo, and May Resp in Osaka and Tokyo. This indicated that MMT for the majority of diseases in these three cities had a high contribution rate for MRadj. in May.

Despite a more temperate environment and higher MMT than Sapporo, Tokyo and Osaka demonstrated a significantly negative MR responseadj. to MMT in May. This could be because the optimum temperature where temperature-sensitive mortality is at its lowest throughout the year varied by region. The team noted that the August MRadj. of cities assessed responded positively to MMT. This observation was also made in Sapporo whose August MMT was considerably lower than Tokyo and Osaka. Therefore, if the temperature in a given year was higher or lower than the ideal climatological temperature of the city, mortality from disease increased.

In Sapporo, an additional 324 to 980 people were expected to die between April and December 2020. This equates to 1.19 to 1.56 times the number of recorded deaths. On the other hand, 651 to 2,653 deaths were predicted in Tokyo between April and December 2020, which is 1.10 to 1.39 times the actual number of reported deaths. In Osaka, an estimated 235 to 1,343 deaths have occurred, which is 1.08 to 1.48 times the number of deaths reported during the same period. In the absence of the pandemic, in Sapporo, Osaka and Tokyo, the death rates corresponding to heat-sensitive diseases would have increased from 19% to 56%, from 8% to 48% and from 10% to 39%.

Conclusion

Overall, the study used data obtained from three major Japanese cities of Sapporo, Tokyo and Osaka, to assess mortality changes related to temperature-sensitive respiratory and cardiovascular diseases during the COVID-19 pandemic.

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