Nearly 11,000 passengers have potentially been exposed to coronavirus on flights in the US, according to research by the Centers for Disease Control and Prevention (CDC).
The American public health body identified that thousands of travellers may have been at risk after investigating 1,600 cases of people who flew while infected with Covid-19.
However, the CDC said it is unable to identify how many people contracted the virus while on flights due to a lack of data.
“CDC is not able to definitively determine that potential cases were associated (or not) with exposure in the air cabin or through air travel given the numerous opportunities for potential exposure associated with the entire travel journey and widespread global distribution of the virus,” said a spokeswoman for the CDC's Division of Global Migration and Quarantine, reports the Washington Post.
"An absence of cases identified or reported is not evidence that there were no cases.“
She added that it can be difficult to prove that people exposed to Covid-19 while flying who then test positive actually contracted the infection on the aircraft, as nailing down the moment of transmission is tricky.
The CDC does not always have access to local health authorities’ testing data either, making it hard to build up an accurate picture of flight-based transmission.
Although modern aircrafts’ advanced air ventilation systems, which pump out fresh air mixed with used air that’s been cleaned by a powerful filter, arguably make planes safer than a busy bar, the proximity to other people for a long period of time does pose a certain amount of risk.
Sitting close to others and potentially touching shared surfaces, in onboard toilets, for example, mean passengers can’t help but be potentially exposed to the virus.
Although data is hard to come by, at least one study proves that Covid-19 can be contracted during air travel, even when travellers are careful.
Published by the CDC, the study was based on evidence collected on an evacuation flight from Milan, Italy, to Incheon, South Korea, and at the government quarantine facility passengers were taken to after landing.
A total of 310 passengers were scheduled to the board the flight on 31 March, at the height of the pandemic.
Pre-boarding, passengers were examined by medical staff at the airport, which involved physical examinations, medical interviews and body temperature checks out of the airport.
Eleven passengers who exhibited Covid-19 symptoms were removed from the flight, while 299 asymptomatic passengers were permitted to board the 11-hour flight to South Korea.
All passengers were given medical-grade masks and kept 2m apart at the airport and on the plane.
“Most passengers wore the N95 respirators except at mealtimes and when using the toilet during the flight,” according to the study.
All passengers were taken directly to a government facility to quarantine when they reached South Korea.
But one 28-year-old woman, who had quarantined prior to the flight and tested negative upon arrival, tested positive 14 days later.
Scientists concluded she could only have contracted the virus while on the plane, with the toilet identified as the most likely place of transmission.
“Our results suggest that stringent global regulations for the prevention of Covid-19 transmission on aircraft can prevent public health emergencies,” said the study’ authors.
The CDC’s official guidance currently states: “Air travel requires spending time in security lines and airport terminals, which can bring you in close contact with other people and frequently touched surfaces.
“Most viruses and other germs do not spread easily on flights because of how air circulates and is filtered on airplanes.
“However, social distancing is difficult on crowded flights, and sitting within six feet of others, sometimes for hours, may increase your risk of getting Covid-19.”