The analysis showed that just over half of adults infected with coronavirus in King County, Wash. in February and March who called 911, received care from rescuers and went to an emergency room had a fever or breathing difficulties.
"Instead, there was a wide range of presenting complaints," Dr. Tom Rea, who co-authored the JAMA Network Open study, told UPI.
Forty percent reported severe fatigue, nearly 28 percent had signs of "altered mental status" -- or confusion -- and up to 10 percent experienced severe nausea and vomiting, the researchers said.
"Hence, there needs to be a wide net of suspicion for COVID,'' particularly among older adults, said Rea, a professor of medicine at the University of Washington.
The findings are based on an analysis of 775 confirmed cases of COVID-19 in King County, which includes Seattle, and was one of the early outbreak hot spots in the United States. The cases were reported between Feb. 1 and March 18.
Researchers said 124 -- or 16 percent -- of the cases included an EMS response. Patients who called 911 and received EMS care were roughly 75 years old, and 47 -- 38 percent -- had three or more chronic health conditions, with high blood pressure and heart disease the most common.
"They can present in a variety of ways, many of them atypical," Rea said. "EMS [needs] to be on alert and assure they are protected and that hospitals are prepared to test this group even when they do not have conventional symptoms."
Fifty-seven -- 46 percent -- of the patients in the study lived in a long-term care facility, though researchers said nonspecific signs and symptoms of COVID-19 were also widely seen in others.
Just over 16 percent required breathing assistance -- with CPAP or another device -- when EMS arrived.
As of June 1, 65 -- 52 percent -- of the patients in the study had died, researchers said.