A U.S. disease surveillance network that monitors doctors’ offices and hospitals has picked up a rise in people with a fever and cough, but who don’t test positive for influenza.
It’s not clear if the increase represents a rise in coronavirus cases that are being missed because of a shortage of testing in the U.S. It’s possible that worried people with some other respiratory illness are showing up for care in greater numbers.
But it’s another piece of evidence as academics, public health experts and the government try to answer what none knows so far — how many people in the U.S. have been infected by the new coronavirus, and how fast is it spreading?
The reports come from states as well as the U.S. Centers for Disease Control and Prevention’s national flu surveillance network. Along with people who test positive for the flu, the networks track patients who show up with “influenza-like illness,” defined as a fever of more than 100 degrees Fahrenheit plus a cough, sore throat, or both. Those are the same symptoms as coronavirus — as well as other illnesses.
Reading the Numbers
One analysis looked at data from the surveillance networks from the last several weeks and found an uptick in symptomatic people seeking health care — but who tested negative for the flu. The trend was most pronounced in the Pacific Northwest, which includes Washington state, the site of the U.S.’s largest number of confirmed coronavirus cases.
“There may be enough community transmission in some states to show up,” said Caitlin Rivers, a professor at Johns Hopkins Center for Health Security who helped lead the analysis. Community transmission refers to ongoing person-to-person spread of a disease.
The analysis looked at visits by patients through March 7. Rivers and her partners said that while it could suggest some relatively small level of currently undiagnosed spread of coronavirus, it would need to be confirmed with testing.
Testing, however, has been a major problem in the U.S. For weeks, hospitals, doctors and local health authorities have complained that there are not enough tests to check all the patients that come in with symptoms. Some people have been told they can’t be tested, and later been diagnosed positive.
While the U.S. government has promised that those efforts will greatly increase with more diagnostic companies offering tests starting soon, the lack of testing during recent weeks was declared “a failing” by Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, a leader of the U.S. response.
Early on, testing was focused on people who fit a narrow set of criteria — such as travel from a foreign country with a significant number of cases, or contact with a known case. There are at least 2,400 confirmed coronavirus cases in the U.S., and at least 50 known deaths, according to data compiled by Bloomberg from state and local reports.
Now that more testing is coming online, many people are testing negative, said Deborah Birx, who is part of the White House’s coronavirus task force. In South Korea, which has widespread testing, about 3% to 4% of tests are positive. In the U.S., tests run by two major lab companies are coming back at about 1% to 2% positive, Birx said at a White House press conference Friday.
All of that makes it difficult to unpack the signal from the noise.
Influenza levels naturally start to fall at about this time every year, said William Morice II, chair of laboratory medicine and president of Mayo Clinic Laboratories, a lab testing group associated with the famed health-care system. The existing flu surveillance system isn’t designed to catch subtle changes that the initial stages of a coronavirus outbreak would create.
“We just don’t know, to be completely honest,” Morice said.
The researchers who analyzed the national data warned that the rise in people going to the doctor could be because of the media attention on the outbreak.
“Media attention could also drive more individuals with mild influenza-like illness to seek care than usual even in the absence of widespread Covid-19 transmission in the U.S.,” they wrote in the analysis, which is being updated as more data roll in.
In New York, a city-level surveillance network showed a similar increase to the analysis conducted by Rivers and her colleagues. The percentage of people showing up at the doctor’s office with influenza- like illness rose to about 5%, up from about 4%, in the week ending March 7, according to a report published by the city’s health department. A similar trend was noticed in emergency room visits. At the same time, the number of people testing positive for the flu declined.
In Washington state the trend was the same. The number of people coming in to health-care providers with flu-like symptoms that week was 6.8%, up from 4% two weeks before. But positive flu tests were down during those weeks, according to the state report.
Lacking widespread testing for the new coronavirus, researchers have attempted to model how many cases there are in the U.S.
One such academic, Trevor Bedford, estimates there could be 10,000 to 40,000 current cases in the U.S. Bedford studies infectious diseases at the Fred Hutchinson Cancer Research Center, a Seattle-based academic center.
“The seeming sudden appearance of outbreaks across the U.S. are not due to a sudden influx of cases,” Bedford said on Twitter. “Transmission chains have been percolating for 4-8 weeks now and we’re just now starting to see exponential growth pick up steam.”
Most people who get the coronavirus experience mild symptoms, and may not even know they have it. They can still pose a wider risk, however, by spreading it to older people or those with underlying health conditions who are more vulnerable. The disease appears to be about 10 times more deadly than the flu, which has about a 0.1% fatality rate, Fauci has said.
— With assistance by Michelle Fay Cortez
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