Why the Number of Heat-Related Deaths May Be Unclear for Weeks

The weekend is expected to bring some relief to parts of the South that have been smothered by a broiling heat wave. But the death toll will probably remain unclear for weeks, if not months: Even though heat-related illness is known to be a leading cause of death from weather or environmental events in the United States, getting an accurate count is difficult.

This is in part because the symptoms of heat-related illness can vary and worsen a patient’s underlying medical conditions, meaning heat-related deaths are often misclassified and thus undercounted, according to the Centers for Disease Control and Prevention.

To find the number of heat-related deaths in Travis County, Texas, for example, one would first have to wait a minimum of 30 days for medical examiner reports to be completed. The next step would be to find the number of cases in which the official cause of death was listed as hyperthermia, or abnormally high body temperature, said Hector Nieto, a county spokesman. But extreme heat can also contribute to a rise in other potentially fatal conditions, like heart failure, and those deaths may be missed.

The county medical examiner’s office categorizes deaths only by cause and manner, not by a potentially precipitating event, Mr. Nieto said. During the state’s brutal winter storm in 2021, it was “impossible for us” to give a winter storm death toll, he recalled. The medical examiner’s office could report only the total number of deaths around the time period, and “from there it was up to somebody else to interpret if that was a winter storm death,” he said.

Determining an accurate death toll can also be complicated in Texas because the vast majority of the state’s counties do not have their own medical examiners’ offices and rely on those in larger counties to determine cause of death.

There is also the more fundamental matter of a state’s willingness to report heat-related deaths, which the C.D.C. says are largely preventable. Texas has not reported a single heat-related death in its prisons since 2012, even though a dangerous lack of air-conditioning in many facilities has been a known problem for years. The Texas Department of Criminal Justice has recorded 32 inmate deaths in what has been a sweltering month. None so far have been attributed to excessive heat.