Community-wide Mortality Rates in Beijing, China, During the July 2012 Flood Compared with Unexposed Periods

Abstract

Background: On 21-22 July 2012, Beijing, China, suffered its heaviest rainfall in 60 years. Two studies have estimated the fatality toll of this disaster using a traditional surveillance approach. However, traditional surveillance can miss disaster-related deaths, including a substantial number of deaths from natural causes triggered by disaster exposure. Here, we investigated community-wide mortality risk during this flood compared with rates in unexposed reference periods.

Methods: We compared community-wide mortality rates on the peak flood day and the four following days to seasonally matched nonflood days in previous years (2008-2011), controlling for potential confounders, to estimate the relative risks (RRs) of daily mortality among Beijing residents associated with this flood.

Results: On 21 July 2012, the flood-associated RRs were 1.34 (95% confidence interval = 1.11, 1.61) for all-cause, 1.37 (1.01, 1.85) for circulatory, and 4.40 (2.98, 6.51) for accidental mortality, compared with unexposed periods. We observed no evidence of increased risk of respiratory mortality. For the flood period of 21-22 July 2012, we estimated a total of 79 excess deaths among Beijing residents; by contrast, only 34 deaths were reported among Beijing residents in a study using a traditional surveillance approach.

Conclusions: To our knowledge, this is the first study analyzing community-wide changes in mortality rates during the 2012 flood in Beijing and one of the first to do so for any major flood worldwide. This study offers critical evidence on flood-related health impacts, as urban flooding is expected to become more frequent and severe in China.

Figure 1.

Daily mortality counts for Beijing residents in July 2012 (red) compared with average mortality counts in July of previous years for (A) all-cause mortality, (B) circulatory mortality, (C) respiratory mortality, and (D) accidental mortality. Shown for comparison are the mean (blue line) of the five-day moving average of mortality, as well as the range (grey area) of daily mortality counts in July of the four previous years (2008–2011). The yellow vertical lines show the peak flood day (July 22).

Figure 2.

Estimates of the relative risk of mortality for four mortality outcomes on the peak flood day (lag 0) and on the four following days (lags 1–4) compared with matched unexposed days from other years, with modeled control for temperature and long-term mortality trends. Dots show point estimates and horizontal lines show 95% confidence intervals. The gray vertical line shows as a reference a relative risk of 1.