Do airport screenings for coronavirus work? CDC program identified only 1 case per 85,000 travelers
According to experts, symptom-based screening programs are ineffective because Covid-19 has a wide range of nonspecific symptoms common to other infections, and there are many asymptomatic cases
As an early effort to prevent the importation of coronavirus, the US Centers for Disease Control and Prevention (CDC) established entry screening at designated US airports for passengers from certain countries. However, a study by the agency shows that temperature and symptom-based screening programs did not help detect Covid-19 cases. They could identify just one case per 85,000 travelers screened. This suggests that passenger entry screening was “resource-intensive with low yield” of laboratory-diagnosed Covid-19 cases. Additionally, contact information was missing for a substantial proportion of screened travelers in the absence of manual data collection.
According to experts, such programs are not effective because coronavirus has a wide range of nonspecific symptoms common to other infections, and there are also many asymptomatic cases. “Symptom-based screening programs are ineffective because of the nonspecific clinical presentation of Covid-19 and asymptomatic cases. Reducing Covid-19 importation has transitioned to enhancing communication with travelers to promote recommended preventive measures, strengthening response capacity at ports of entry, and encouraging pre-departure and post-arrival testing. Collection of contact information from international air passengers before arrival would facilitate timely post-arrival management when indicated,” write authors.
In January 2020, with support from the US Department of Homeland Security (DHS), the CDC instituted an entry risk assessment and management (screening) program for air passengers arriving from certain countries with widespread, sustained transmission of coronavirus.
On January 17, entry screening of air passengers arriving from Wuhan, China, the epicenter of the coronavirus outbreak at the time, began at three US airports: Los Angeles International Airport, California; San Francisco International Airport, California; and John F Kennedy International Airport, New York City.
Beginning February 3, entry screening was expanded to all passengers arriving from mainland China after the issuance of a presidential order restricting entry to US citizens, lawful permanent residents, and other excepted persons. These travelers were routed to one of 11 designated airports. On March 2, travelers from Iran were added. As Europe became a new epicenter of coronavirus, travelers from 26 countries in the European Schengen Area (effective March 14), the UK, and Ireland (effective for both March 17) were added, and the number of airports to which passengers were routed expanded to 13. When travelers from Brazil were added on May 28, screening expanded to 15 designated airports.
The aim was to reduce the importation of coronavirus cases into the US and slow subsequent spread within states. Screening aimed to identify travelers with Covid-19-like illness or who had a known exposure to a person with coronavirus and separate them from others. Screening also aimed to inform all screened travelers about self-monitoring and other recommendations to prevent disease spread and obtain their contact information to share with public health authorities in destination states.
What did the study find?
During January 17-September 13, 766,044 travelers were screened, out of which 298 (0.04%) met the criteria for public health assessment. This is because travelers had either been in Hubei Province (16, 5.4%), reported contact with a person with Covid-19 (four, 1.3%), or had signs or symptoms that triggered a public health assessment (278, 93.3%).
Among the 278 persons who had coronavirus-like symptoms, the most common signs or symptoms triggering assessment were cough (73%), self-reported fever (41%), measured fever (17%), and difficulty breathing (13%). According to researchers, 40 (14%) of these travelers were medically evaluated at a local healthcare facility, and 35 (13%) were tested for Covid-19. Nine of the 35 tests returned positive results, representing 0.001% or 1 per 85,000 of all travelers screened.
Fourteen additional travelers with laboratory-confirmed coronavirus were identified through other mechanisms rather than as a direct result of entry screening: six via established processes with airlines and airport partners to detect ill travelers and notify CDC, and eight through notifications about travelers who had received a positive test result in the US or another country before travel.
The agency relied initially on existing federal traveler databases to obtain passenger contact information to share with states, but missing or inaccurate data prompted adding manual data collection to the screening process. Manual data collection resulted in 98.1% complete records (phone number and physical address). The CDC sent state health departments contact information for approximately 68% of screened travelers.
“These findings demonstrate that temperature and symptom screening at airports detected few Covid-19 cases and required considerable resources. Reasons for the low yield were likely multifactorial and might have included an overall low Covid-19 prevalence in travelers, the relatively long incubation period, an illness presentation with a wide range of severity, afebrile cases and nonspecific symptoms common to other infections, and asymptomatic infections. (Another reason maybe) travelers who might deny symptoms or take steps to avoid detection of illness (for example through the use of cough suppressant medications),” the team explains.
Stating that the hallmark of effective public health programs is a reassessment of methods used for public health practice based on available evidence, the CDC recommended a shift from the resource-intensive, low-yield, symptom-based screening of air travelers, and on September 14, the screening program was discontinued.
The CDC currently recommends that all travelers should follow its recommendations for mask use, hand hygiene, self-monitoring for symptoms, and social distancing during travel and after arrival to the US. Travelers with higher exposure risk are advised to take additional precautions, including post-arrival testing, avoiding contact with persons at higher risk for severe disease, and staying home as recommended or required by jurisdictional public health authorities. The agency has also enhanced the public health response capacity at ports of entry.
“Pre-departure testing of travelers, ideally with specimen collection within 72 hours before departure, might reduce the risk for coronavirus transmission during travel. Post-arrival testing could allow for shortening of post-travel self-quarantine periods that protect against travel-associated imported (translocated) infections. Finally, progress in understanding immunity biomarkers and duration of protection, in developing one or more vaccines, and in testing hold promise for refining risk stratification and optimizing management of travelers to reduce Covid-19 transmission and translocation related to commercial air travel,” conclude authors.