Body temperature may not really gauge COVID

I went to get a coronavirus test after Thanksgiving, and the nurse took my temperature — 97.7 degrees Fahrenheit. This is not unusual for me, even though it was lower than what we think of as normal.

Normal body temperature is one health-related number that most everybody knows — 98.6 degrees. It’s even easier in Celsius — a flat 37 degrees.

Despite the exactitude of the widely accepted number, down to one-tenth of a degree, body temperature is not that fixed.

A recent study compiled data from 150,280 adult outpatient visits to Stanford Health Care facilities over a 10-year period. The average temperature was 98.0 degrees for men and 98.2 degrees for women.

Another recent study, of 96 adults, found an average temperature was 97.0 degrees. And a 2017 study, of 35,488 adults, came up with an average of 97.9.

These results lead to two key observations: Temperature is pretty variable. And if anything, average human body temperature is typically less than the long-accepted 98.6.

“The number comes from a mid-19th-century study,” says Julie Parsonnet, an infectious-disease physician at Stanford University School of Medicine. In that study, a German physician, Carl Wunderlich, collected a million temperature readings from many thousands of patients and published this average: 98.6 degrees.

“Wunderlich was a giant in the field,” says Philip Mackowiak, professor emeritus at the University of Maryland School of Medicine and an expert on fever and body temperature. He points out that while 98.6 was the “average,” Wunderlich never called it “normal.”

Indeed, most doctors know that a person’s body temperature varies across the day and over the life span. “Your temperature is likely to be lowest in the morning,” Parsonnet says. “Women tend to be warmer than men, and temperature tends to drop with age.”

Body temperature can fluctuate in very cold or warm conditions and with activity such as exercise, Mackowiak says. In addition, he says the very term body temperature is a misnomer, as it depends on what part of the body one measures: mouth, ear, armpit or rectum.

Still 98.6 has persisted. “People want simple answers even when the question is complex,” Mackowiak says.

The variability in reallife temperature readings is one reason 99 degrees is not generally considered a fever. Most organizations use 100 degrees (or higher) as a threshold temperature at which students shouldn’t go to school and employees shouldn’t go to work.

Parsonnet knew that modern studies consistently found average body temperatures that were lower than 98.6 and she wondered what accounted for the difference. Better thermometers? That today’s doctors tend to use oral readings rather than the under-the-arm method that Wunderlich used in 1851? Or have we humans changed in some fundamental way?

Parsonnet and her team studied three data sets: one from Civil War veterans up to 1930, another from a U.S. survey in the early 1970s, and her own data from Stanford clinics starting in 2007.

She documented a steady decline in average body temperature over the decades.