Objective  To examine the impact of extreme apparent temperature (AT) on daily emergency visits for hypertension in Shenzhen city, Guangdong province for providing evidence to revision of public health policies relevant to hypertension management and ambulances allocation.

  Methods  The data on daily emergency visits for hypertension from January 2013 to December 2020 were collected from the Shenzhen First-Aid Service Platform and daily meteorological data of Shenzhen city over the same period were collected simultaneously for the estimation of daily average AT. Distributed lag nonlinear model (DLNM) was used to analyze the lag day and lag period effects of extreme AT on daily emergency visits for hypertension. Relative risk (RR) and population attributable risk percent (PARP%) were adopted in estimating the effects.

  Results  During the 8-year period in the city, totally 14 491 outpatient emergency visits for hypertension occurred based on the records of the platform; the daily number of visits ranged from 1 to 28 and the average number of daily visits was 9.28 ± 0.90. During the same period for the city, the lowest daily average AT was – 4 ℃ and the highest was 39.4 ℃, with an average AT of 25.62 ± 7.95 ℃. A nonlinear effect of extreme AT on daily emergency visits for hypertension was observed; the number of the daily visits decreased with daily average AT but increased with daily average AT when the daily average AT being 30 ℃ and above. The results of DNLM analysis showed that in comparison to appropriate AT (30 ℃), both extreme low AT (9 ℃) and extreme high AT (36 ℃) were associated with an increased risk of daily emergency visit for hypertension during the lag period of 0 – 21 day, with the relative risk (RR) (95% confidence interval 95%CI) of 1.783 (1.303 – 2.433) and 1.315 (0.994 – 1.747); the lag effect of the extreme low AT was much stronger on the daily emergency visits of male hypertension patients and those aged under 65 years, with the RR (95%CI) of 1.721 (1.050 – 2.811) and 1.872 (1.184 – 2.982), respectively. The PARP of extreme low AT-related daily emergency visits for hypertension was 13.64% generally for the study period.

  Conclusion  The extreme AT is of significant impact on daily emergency visit of hypertension patients in Shenzhen city, especially for the male patients and the patients aged under 65 years.