CDC: Screening at SFO didn’t stop coronavirus.
Volume of travelers, possibility of asymptomatic carriers among hurdles to effective monitoring
The health screening of travelers from China and Iran created an elaborate system of temperature checks and interviews as flights were funneled through San Francisco International Airport and other busy travel hubs.
What it didn’t do: Stop COVID-19.
“Despite intensive effort, the traveler screening system did not effectively prevent introduction of COVID-19 into California,” the U.S. Centers for Disease Control and Prevention concluded in a report released Monday.
Only three of the 11,547 international travelers reported to local health departments for follow-up after landing at California airports from Feb. 3 to March 17 ended up on the state’s list of more than 26,000 cases of coronavirus by mid-April.
Two had traveled from Iran and the third from China.
The report reveals the challenge of trying to hermetically seal off a nation.
“We knew the importance of cases that were occurring overseas. And we were trying to deal with that. But we didn’t know what we were doing,” said Dr. John Swartzberg, clinical professor emeritus of infectious diseases and vaccinology at UC Berkeley’s School of Public Health.
“We used an awful lot of resources in a very uncoordinated way to try to solve the problem — when it was already too late,” he said.
Monitoring travelers was laborintensive and limited by incomplete information, the volume of travelers and the potential for asymptomatic transmission, according to the report.
The Return Traveler Monitoring team, staffed by the California Department of Public Health, required 1,694 “person hours” — the equivalent of six people working full-time for seven weeks.
President Donald Trump has said his administration slowed the spread of the coronavirus into the United States by acting decisively to bar travelers from China and Iran on Jan. 31. But there were delays in screening passengers from Italy and South Korea, despite climbing COVID-19 cases in those countries.
In hearings last week, a Democratic-led U.S. House of Representatives subcommittee said information from several U.S. agencies found the screening program did little to stop the spread of the virus through U.S. airports.
In recent weeks, many countries, including the United States, have imposed travel restrictions to help curb the spread of the coronavirus.
Airport closures, the suspen
sion of all incoming and outgoing flights, and nationwide lockdowns are some of the measures countries are adopting in an effort to help contain the pandemic.
Traveler screening for COVID-19 has a major challenge: It does not detect infections that are asymptomatic. Health screening at airports is most successful when infected travelers can be readily identified, according to the CDC.
For example, monitoring for Ebola from Africa in 2014-2015 was effective because the illness has obvious clinical symptoms. And Ebola is contagious only after symptoms appear.
Screening is also easier if there is a relatively small number of travelers who need to be tracked.
During the Ebola outbreak, only 21 travelers per week from three disease-affected countries in Africa were monitored, on average, in California.
That compares to the 1,431 travelers who had to be monitored each week for signs of COVID-19.
Additionally, the effectiveness of California’s program was limited by incomplete traveler information received by federal officials and reported to states, as well as the number of travelers needing follow-up, the report found.
About 13% of records had errors and had to be corrected.
These ranged from incorrect U.S.-based telephone numbers to insufficient location data, misspelled names or wrong birthdates. Some records were duplicates.
Flight manifests or other independent records to verify traveler information were unavailable.
This delayed efforts to reach travelers — and some travelers were completely lost to authorities.
To succeed, such programs need more efficient methods of collecting and transmitting passenger data, so that local health jurisdictions can reach at-risk travelers quickly, according to the CDC. This would ease quick testing, case identification and “contact tracing” investigations.
The effectiveness of airport screening may also depend on the phase of a pandemic.
It’s most effective early on, when containment is possible.
But it also could be helpful in the future, as community transmission decreases and our borders once again need protection, according to the CDC.
“We’ve learned so much. With technology improving, in terms of sampling and testing, this might be an area that would help a little bit. But it’s not the first place to put resources,” cautioned UC Berkeley’s Swartzberg.
“The virus is here. People bringing it in — that’s a really teeny part of the problem,” he said. “We’re closing the barn doors after the horse has left.”