Heat Mortality, Mortality Displacement and SARS CoV-2

Biostatistics (Public Health); Environmental Health (Public Health); Climate

The timing of SARS CoV-2 and summer, 2020 heat waves provides a rare opportunity to examine heat related mortality, as heat waves and the SARS CoV-2 virus impact similar segments of the population.

Research Interests
  • Weather, climate, and human health
  • environmental health

Heat waves are the main cause of weather-related mortality in the United States, primarily impacting the elderly, infants, and individuals with certain comorbid conditions.  Daily mortality peaks are well-correlated with peaks in heat and humidity, with typical lags of one day or less.  Because heat waves impact the most vulnerable members of the population, there is often a notable and statistically significant decline in mortality for a period of days following the heat wave mortality peak, as the population is less vulnerable to heat.  Thus, the heat-related deaths were displaced forward in time.

A clear understanding of the impact of weather on health requires an accurate accounting of these events.  Heat impacts are often underestimated when only heat stroke is retrospectively examined in death certificates, as heat is routinely ignored in autopsy reports.  However, heat impacts are also overestimated when mortality displacement is not considered.  Literature estimates of heat displacement range from zero (none of the deaths are displaced) to 100% (all of the people were likely to die in the near-term).   Furthermore, displacement varies spatially based upon the adaptation of various communities to heat impacts.

Despite its importance in understanding the net impact of heat waves on health, mortality displacement research is incomplete.  The ongoing SARS-Cov-2 pandemic provides a rare opportunity to resolve the confusion associated with heat-related mortality displacement and thus provide a more definitive understanding of the net impact of heat on human mortality. 

In the United States, mortality from the pandemic began regionally in February and March of 2020, and by May had spread throughout much of the country.  Deaths from the SARS-CoV-2 virus occur primarily among the elderly population (median age is 80) and among individuals with a variety of comorbidities, including diabetes, COPD, heart disease, kidney disease, and  the immuno-compromised, all of which are characteristics also associated with heat-related mortality.  Furthermore, spring and summer of 2020 saw widespread heat waves across much of the continental United States, in some cases with unprecedented duration.

 The timing of the pandemic and subsequent heat waves thus provides a unique, perhaps once-in-a-lifetime, research opportunity to examine mortality displacement.  As the pandemic was linked with significant mortality among a population that is similarly most susceptible to heat, the resulting heat waves should have shown a markedly lower mortality than would typically be expected.  We would thus hypothesize that heat waves in the summer of 2020 would exhibit significantly lower mortality as compared to prior, comparable heat waves, because of mortality displacement associated with the pandemic.  

We propose to examine this hypothesis first in the Commonwealth of Virginia, as both the heat wave and pandemic impacts vary significantly over time and space.  For example, some areas of the Commonwealth exhibited high pandemic mortality in April and May while others did not.  How did mortality in the summer, 2020 heat wave compare to prior heat waves?  Was there any heat-related mortality?  If there was, what comorbidities were expressed in that population?

We would furthermore compare the timing of the 2020 heat waves to the intensity of timing of pandemic mortality.  Did locations that were largely spared of pandemic-related deaths see higher heat-wave mortality than other locations where pandemic deaths were high?  Are there any relationships between the timing of pandemic deaths (early vs. late spring or summer peak) and the timing of heat waves?  This kind of analysis could provide insight into the time required for the population affected by a shock event (like a pandemic or heat wave) to recover and return to its baseline vulnerability.

 

Desired outcomes

More accurate estimates of the toll of heat on human mortality in Virginia relative to the roll of mortality displacement.

Better estimates of years of life lost from heat and heat waves as a function of comorbid factors.

Better estimates of the varying impact of heat and heat waves or mortality and mortality displacement in different geographic areas of Virginia.