Americans are suffering through a very bad cold season — but not a terrible flu season, which would be far more threatening, according to the makers of a smart thermometer that accurately tracked last year’s highly lethal flu season.
Nearly 1 million American households use Kinsa Health’s internet-connected thermometers and they submit about 40,000 readings a day. This week, about 10 percent more Americans have fevers than did even at the peak of last year, the company said.
“Lots of people are sick — but they have colds, not flu,” said Inder Singh, founder of Kinsa Health, in a telephone interview.
The company made that conclusion, he said, based on how long the fevers lasted. Typically, a cold’s fever lasts only a day or two, while the fever that accompanies flu lasts three to seven days.
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The Centers for Disease Control and Prevention had no comment Thursday night on Mr. Singh’s assessment, although the agency has expressed interest in the thermometers and the maps he generates from their data.
The C.D.C. normally tracks flu season by collating weekly reports from doctors about how many patients come in with flu symptoms, and how many are hospitalized with it. So the agency’s data lags the on-the-ground reality by up to two weeks.
Kinsa, by contrast, gets fever data almost instantly; additionally, parents and other users can enter other symptoms into the company’s app. In theory, Kinsa may be able to rapidly track an outbreak of norovirus, for example, which typically causes moderate fevers but profuse vomiting.
In mid-January last year, Mr. Singh predicted that the 2017-2018 flu season would be quite severe while the C.D.C. was still forecasting one of “moderate severity.”
At that point, only a small number of Americans had been hospitalized. But the thermometers were tracking high, long-lasting fevers spreading from California to the Midwest.
After the season ended, the C.D.C. said it had been the worst in more than a decade and estimated that it killed about 80,000 Americans. (A typical season kills 20,000 to 30,000.)
The dominant strain last year was H3N2, which tends to be more deadly; thus far this season, the dominant strain is a descendant of the novel H1N1 strain that first appeared in 2009. That strain was very infectious, but not very lethal.
The polar vortex that struck the Midwest in late January actually slowed the transmission of colds and flu, Mr. Singh said — presumably because so many schools were closed. But it shot up starkly within days after schools reopened and children were back in classrooms together.
Mr. Singh also predicted that this year’s flu season is peaking right now.
“The number of illnesses lasting longer than three days rose massively in the last few days,” he said. “That inflection point is typically an indication that flu season is about to peak.”
According to the C.D.C.’s weekly FluView, flu typically peaks in mid-February. If Mr. Singh is correct that the season is peaking now, it will most resemble the 2016-2017 season, which was moderately severe.
At the moment, the sickest areas in the country are Texas and Louisiana, where more than 8 percent of people are ill, according to Kinsa. In New England, 7 percent of people are running fevers.
