Download:
-
Tropical cyclone (TC) is significantly and adversely associated with both accidental and non-accidental mortality (1-2). Additionally, accidental deaths from drowning, physical trauma, and electrocution during TCs have been well characterized in epidemiologic studies. However, whether heterogeneity exists in TC-associated risk for non-accidental mortality sub-causes remains unclear. Recognizing non-accidental mortality sub-causes susceptible to TCs is essential for devising mitigation. While the longer-term effect of TCs on non-accidental mortality, such as circulatory mortality, has been recognized (2), little is known about the short-term non-accidental mortality risk of TCs.
TC’s complex features generally stimulate cascading responses affecting non-accidental disease mortality (3). There is evidence that TC could substantially increase the risk of non-accidental mortality. The associated risks could result from several pathways; for example, TC can cause problems in accessing medical care (3), can damage infrastructure including public transportation and utility systems, and can increase exposure to other hazards like extreme heat.
We examined short-term associations of TC with mortality outcomes in China. China’s relatively high daily mortality enables the statistical analysis of rare health outcomes (4). Specifically, we aimed to 1) quantify TC-associated mortality risk and identify sensitive sub-causes; 2) recognize vulnerable sub-population and regions.
-
From the China Mortality Surveillance System of the National Center for Chronic and Noncommunicable Disease Control and Prevention, China CDC, we obtained mortality data, including residents’ daily mortality for 280 Chinese counties from 1 January 2013 to 31 December 2018 (
Supplementary Figure S1 ). The International Classification of Diseases classified mortality data, 10th Revision (ICD–10), including all-cause (A00–Z99), non-accidental (A00–R99), accidental (V00–X56), circulatory (I00–I99), and respiratory diseases (J00–J99). We also included mortality data due to 18 sub-causes (Supplementary Table S1 ).We obtained TCs data from the Tropical Cyclone Information Center of the China Meteorological Administration. For each TC event, we classified a county as exposed if the storm’s central track came within 60 km of the county’s geographic center (
Supplementary Figure S2 ). Meteorological data were collected from the European Centre for Medium-Range Weather Forecasts.A case-crossover study design was used to examine the county-level association between TCs and mortality. Each exposed day was matched to five unexposed days by county. We considered TC-associated risk up to six following days (1). Using the matched multi-county data, we fit generalized linear mixed-effect models (GLMMs) with a Poisson distribution to estimate TC-associated mortality risk (expressed as rate ratio, RR), adjusting for potential confounders. An unconstrained distributed lag function was used for the TC exposure variable. A county-specific random intercept was included.
We performed stratified analyses by sex, age, and the subset of counties by TC exposure frequency. We conducted sensitivity analyses to investigate the model’s robustness. All the statistical analyses were completed using R (Version 3.6.1, The R Foundation for Statistical Computing). More details are provided in the Supplementary Materials.
-
China was hit by forty-six TCs during 2013–2018 (Figure 1). 153 out of 280 counties were exposed to at least one TC and were analyzed. Southeast coastal areas were frequently affected (Figure 1). The total counts of all-cause mortality were 4,147 and 20,062 on TC-exposed days and selected five reference days, respectively (Table 1).
Figure 1.Spatial distribution of 153 eastern Chinese counties (blue circles) that were exposed to at least one tropical cyclone over the study period (2013–2018).
Note: Curves show the tracks of the 46 tropical cyclones that made landfall on China continent in this period; color of storm tracks denotes the maximum wind speed. Color of the circle in each county indicates the frequency of tropical cyclone exposures during the study period.Variable Exposure days (N=336) Reference days (N=1,680) Total Mean±SD Median (P25, P75) Maximum Total Mean±SD Median (P25, P75) Maximum All-cause 4,147 12.3±7.9 10 (7, 17) 48 20,062 11.9±7.6 10 (6, 16) 43 Cause-specific Non-accidental 3,844 11.4±7.3 10 (6, 15) 40 18,472 11.0±7.0 10 (6, 15) 39 Accidental 303 0.9±1.2 1 (0, 1) 8 1,590 1.0±1.2 1 (0, 1) 7 Circulatory disease 1,648 4.9±3.9 4 (2, 7) 26 7,557 4.5±3.4 4 (2, 6) 24 Respiratory disease 449 1.3±1.5 1 (0, 2) 8 2,323 1.4±1.5 1 (0, 2) 8 Sex Male 2,405 7.2±4.9 6 (4, 10) 28 11,471 6.8±4.6 6 (3, 10) 28 Female 1,742 5.2±3.7 4 (2, 7) 20 8,591 5.1±3.8 4 (2, 7) 23 Age (years) 0–64 964 2.9±2.4 2 (1, 4) 17 4,826 2.9±2.3 2 (1, 4) 14 65–74 802 2.4±2.1 2 (1, 3) 11 3,907 2.3±2.0 2 (1, 3) 12 >75 2,381 7.1±5.0 6 (3, 10) 24 11,329 6.7±4.8 6 (3, 9) 29 Note: N=the number of TC exposure days. Table 1. Summary statistics of daily mortality on tropical cyclone exposure days and reference days (exposure∶reference=1∶5) in 153 Chinese counties (2013–2018).
Compared with reference days, TC-associated RRs for all-cause and non-accidental mortality were 1.07 [95% confidence interval (CI): 1.03–1.10] and 1.08 (95% CI: 1.04–1.11) at lag 0 day (the exposure day), respectively. Although accidental mortality did not increase on the TC-exposed day, it did by the third day following exposure (RR=1.18, 95% CI: 1.06–1.30). We found significant associations at lag 0 between TC exposure and circulatory mortality (RR=1.12, 95% CI: 1.06–1.18) and respiratory mortality (1.12, 95% CI: 1.01–1.23) (
Supplementary Table S2 ,Supplementary Figure S3 ). Effect estimates from sensitivity analyses were consistent with the primary ones (Supplementary Table S3 ).TC was associated with increased risks for several mortality sub-causes at lag 0 day, including ischemic heart disease, myocardial infarction (MI), cardiac arrest, cerebrovascular disease, stroke, chronic obstructive pulmonary disease (COPD), and Parkinson’s disease; for example, MI mortality risk increased by 15% (Figure 2). The estimated RRs remained elevated for mortality due to cardiac arrest, cerebrovascular disease, and stroke in the subsequent 2–3 days. We also observed appreciable lagged effects for lower respiratory infection, asthma,influenza, and pneumonia (Figure 2).
Figure 2.Lag-specific rate ratio of sub-cause mortality associated with tropical cyclone exposure, on average across all exposed counties.
Males had a higher TC-associated risk for accidental and circulatory mortality than females but lower for respiratory mortality (
Supplementary Figure S4 ). The difference in risk estimates by sex was not statistically significant. Residents aged 65–74 years presented a significantly lower respiratory mortality risk than those younger than 65 and older than 74 years. We observed a higher cardiorespiratory mortality risk in counties that experienced ≥3 TC events than in those experiencing 1–2 events and lower accidental mortality risks, though the difference was not significant (Supplementary Figure S4 ).
HTML
-
To the best of our knowledge, this is the first multi-center, multi-event study examining the short-term associations of TCs with many mortality outcomes in China. Among residents in 153 Chinese counties during 2013–2018, TCs were associated with elevated risks for several non-accidental mortality, especially circulatory and respiratory sub-causes. TCs were also associated with renal failure and Parkinson’s disease mortality. Our findings suggest an urgent need to expand the public health focus of natural disaster management to include non-accidental mortality outcomes.
Two similar Chinese studies existed but on a much smaller scale. One study reported a RR of 1.05 (95% CI: 0.96–1.16) for circulatory mortality associated with TCs in Guangzhou (2008–2011) (5). The other indicated elevated mortality risk during the two years following Typhoon Morakot (2009) in Taiwan (6). These reported longer-term TC-associated mortality risks were consistent with western studies (2). However, TC-associated circulatory mortality risk was much more substantial in the short term, with a 12% increase on the TC-exposed day in this study and a 1.2% increase in the following month from a previous study (2). Our findings complement the limited knowledge by providing evidence of TC’s short-term circulatory mortality risk, focusing on a time scale relevant to rapid public health response.
Mortality due to several circulatory diseases markedly increased in association with TC. TC immediately impacted cardiac arrest and MI mortality. It is known that TC may have a longer-term effect on MI; for example, 30-day MI mortality increased by 31% during Hurricane Sandy in New Jersey (7). We found MI mortality increased by 15% on TC-exposed days, suggesting a short-term risk of TC. Psychological stress after TC exposure may help explain the elevated risk associated with TC. TC occurrences typically generate psychological stress for affected individuals, provoking physiological responses. Among these responses, the hypothalamic-pituitary-adrenocortical and autonomic nervous system responses primarily contribute to cardiovascular disease development (8). Stress may also trigger stroke, a possible explanation of TC-associated increased risk of cerebrovascular disease and stroke mortality (9). Our findings suggest an urgent need to expand the public health focus of TC management to include circulatory sub-causes.
Accidental deaths (like drowning and being hit by falling tree limbs) often occur during TC (10). We only observed increased accidental mortality risk at lag day 3 (RR=1.18). During TCs, fatal injuries or drowning often occur in heavily impacted areas where strong winds and severe rainfalls may block roads and damage communications. Therefore, the rescue teams might not arrive in time, and the deceased had to be determined a few days later. It may also be possible that it took several days to find and identify all accidental deaths caused by TCs. Furthermore, though insignificant, TC-associated accidental mortality risk was higher in males than females, which is consistent with previous findings. For example, the ratio of males to females was 1.87/1.00 among victims of Hurricane Sandy. Occupation type by sex might be a reason for this result, as men dominate some jobs (like bus drivers and rescue team members) with higher health risks than others during TCs.
TC was also associated with an increased mortality risk due to lower respiratory infections, COPD, influenza and pneumonia, renal failure, and urinary system diseases. While the underlying mechanism is not adequately understood, TCs likely affect mortality through damaging infrastructure (3). First, TCs can damage transportation and communication infrastructure, which may impede people from seeking medical treatment. Beyond that, utilities and power outages play a crucial role in increasing the risk of death for patients relying on electrically powered medical technologies like ventilators and oxygen, especially for those at hospitals who are particularly vulnerable to the impact of power outage (3).
Parkinson’s disease mortality significantly increased on TC days but not in the next few days. External shocks and movement difficulties may partly explain the elevated mortality risks. According to a previous study on TCs’ effects on Parkinson’s disease in American older adults, the hospitalization rate for Parkinson’s disease increased in the week after TCs (2). It can be possible that patients with severe Parkinson’s disease might be extremely fragile to the impacts of tropical cyclones and more likely to die than those who had less severe conditions and could be hospitalized in the following days.
Our study has some limitations. First, exposure misclassification may exist. Previous research has evaluated TC-associated health risks in America using a multi-hazard-based exposure assessment (1–2). Distance from a storm track effectively captured some signal of TC’s health risk (1). Future research is needed to develop alternative methods of TC exposure assessment in China. Second, confounding residuals may be possible. We used a matched design by county; county-level confounding factors that were time-invariant could be controlled at the study design stage. However, some county-level confounders (such as socioeconomic characteristics) could be time-variant. So confounding residuals may exist in the results (2).
Our findings offer practical implications. Firstly, it is crucial to improve TC’s early warning system, which should be able to alarm vulnerable individuals to take proper measures. The authorities should provide adequate medical resources for affected residents, especially people with TC-associated sensitive diseases. Also, the public should be well educated about TC’s health risk.
-
No conflicts of interest.
| Citation: |
|