Nov. 12 (UPI) -- Symptom-based screening programs implemented a U.S. airports at the start of the COVID-19 detected just nine cases of the virus among more than 766,000 travelers, according to data released Thursday by the Centers for Disease Control and Prevention.
During the program, which was in effect from Jan. 17 to Sept. 13, only 298 -- or 0.04% -- of the travelers met the criteria for enhanced screening and just 35 underwent COVID-19 testing, CDC researchers reported.
The findings suggest that "most infected travelers [went] undetected by symptom-based screening at airports" and were therefore able to unknowingly spread the virus within their "destination communities," they said.
"Because ... infection and transmission can occur in the absence of symptoms and because the symptoms of COVID-19 are nonspecific, symptom-based screening programs are ineffective for case detection," the CDC researchers wrote.
On Jan. 17, the CDC, working with the U.S. Department of Homeland Security, began to screen passengers arriving from Wuhan, China -- the "epicenter of the COVID-19 outbreak at the time" -- at Los Angeles International Airport, San Francisco International Airport and John F. Kennedy International Airport in New York City.
By Feb. 3, the initiative was expanded to include all passengers arriving from mainland China, all of whom were routed to one of 11 designated airports, according to the CDC.
On March 2, travelers from Iran were added to this list, as were travelers from 26 European countries less than two weeks later.
As of May 28, the screening program was expanded to 15 airports and included travelers from Brazil.
At the same time, the CDC issued a series of advisories designed to discourage travel to and from the United States because of the pandemic.
The symptom-based airport screening program was discontinued on Sept. 14, according to the agency.
Instead, the CDC's strategy "has transitioned to enhancing communication with travelers to promote recommended preventive measures," including the wearing of face coverings while in transit, and "encouraging pre-departure and post-arrival testing," the researchers said.
"Airport-based activities may have led travelers to take actions to prevent the spread of COVID-19, including by staying at home for 14 days after arrival," they wrote.
"However, the low number of COVID-19 cases detected through symptom-based screening programs highlighted the need for fundamental change in the U.S. border health strategy," they said.