Does the Passenger Next to You Have COVID?

A growing proportion of COVID-19 infections in travelers may be asymptomatic, according to data from Chinese researchers.

From April to October 2020, less than 0.1% of all travelers entering China tested positive for SARS-CoV-2, but the proportion of asymptomatic infections in these cases rose from 27.8% in April to 59.4% in October (P<0.01), reported Zunyou Wu, MD, PhD, of the Chinese Center for Disease Control and Prevention in Beijing, and colleagues.

“The finding of a high and increasing proportion of asymptomatic infections among all SARS-CoV-2-positive international entrants to China may signal an increase in asymptomatic infection globally,” the authors wrote in a JAMA research letter. “This study has implications for traveler screening policies and procedures.”

Researchers noted China implemented mandatory screening for SARS-CoV-2 of people traveling into the country via air, sea, or land at border checkpoints beginning on April 1, 2020. Those who tested positive were hospitalized for isolation, while those who tested negative were required to quarantine for 14 days before being retested on day 13.

The U.S. is attempting to enact more stringent travel guidance of its own. CDC recently required international air travelers to the U.S. to provide proof of a negative COVID-19 test, and has been weighing requiring a COVID-19 test prior to domestic flights, though travel industry groups are pushing back on these proposed regulations. A federal mask mandate for federal travel — including planes, trains, and boats — and transportation hubs went into effect on Feb. 1.

In the current study, Wu and colleagues examined data from over 19 million travelers entering China from April to October 2020. Overall, 3,103 (<0.1%) people tested positive for SARS-CoV-2. About three-quarters were men, and around 80% were ages 20 to 49. Among those testing positive, 43.6% were symptomatic (dropping from 71.0% in April to 35.9% in October), about 4.4% were pre-symptomatic (or developed symptoms soon after being tested, increasing from 1.2% to 4.7% over the study period) and 52% were asymptomatic. There was a significant association between presence of symptoms and age.

Interestingly, the authors noted that 44% of SARS-CoV-2-positive entrants arrived from four of 86 countries.

Limitations to the data include the inability to detect how many symptomatic individuals were screened in due to prior infection and prolonged viral shedding or how many symptomatic individuals were screened out, the authors said.