Study Shows How Easily SARS-CoV-2 Can Spread on a Flight

Doug Brunk

February 08, 2021

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It's no secret that SARS-CoV-2 can be spread during airline flights, but a new analysis designed to assess possible points of infection on a long-haul flight from Dubai, United Arab Emirates, to New Zealand last fall demonstrates just how easy it is to contract the virus.

Dr Joep de Ligt

The study, which was published online January 5 in Emerging Infectious Diseases, "shows just how transmissive this virus is and that we should all be doing our best to reduce transmission where and when we can," one of the study authors, Joep de Ligt, PhD, manager of bioinformatics and genomics at the Institute of Environmental Science and Research in Porirua, New Zealand, told Medscape Medical News. "Another important message is that, while useful, a negative preflight test is not a guarantee that people will not carry or contract the virus. If people have to fly, they should be advised to take all possible precautions."

In March 2020, New Zealand closed its borders to all but its citizens, permanent residents, and those who had received an exemption. In April, the country implemented a policy of managed isolation and quarantine (MIQ) at the border. This required individuals who arrived in New Zealand to stay in a government-assigned facility for at least 14 days before entering the New Zealand community.

In June, the country's health officials began to test people who were returning to New Zealand and were staying in MIQ facilities. Nasopharyngeal swabs were taken on the third and the 12th day of the quarantine period. Health officials also tested anyone who developed symptoms or who were identified as having come into close contact with people whose SARS-CoV-2 test results were positive.

As of October 2020, testing of people in MIQ had identified 215 persons infected with SARS-CoV-2 among 62,698 arrivals. Of these 215 persons, seven had arrived on an Emirates flight of 86 passengers that had left Dubai on September 28 and had arrived in Auckland, New Zealand, on September 29. The flight made a refueling stop in Kuala Lumpur. The passengers originated from five countries ― Switzerland, Ireland, Ukraine, South African, and India. There was a layover in Dubai. To assess possible points of infection, the researchers, with consent from the seven affected passengers, analyzed information about their journeys and disease progression as well as virus genomic data.

Comprehensive Data

"Our study was one of the first with comprehensive evidence of in-flight transmission while protective measures like mask and glove wearing, plus predeparture testing, were in play," de Ligt said. "The integration of both detailed epidemiological and genomics data meant that we could draw conclusions about how and where the infections happened. Most countries don't have the time and resources to perform such detailed analysis, and as such, the study provides an important piece of data for policymakers internationally when evaluating the transmission risks for flights."

Five of the seven passengers reported that they had tested negative before departure. All seven were seated within four rows of each other during the flight. No passengers entered or exited the aircraft during the 2-hour refueling period in Kuala Lumpur. During the flight and before departure from Dubai, mask use wasn't mandatory. Five passengers self-reported using masks and gloves while on the airplane; two did not use them.

After the researchers evaluated epidemiologic data, the in-flight seating plan, symptom onset dates, and genomic data from these seven travelers, they determined that two passengers were likely index case-patients who had become infected before the flight; four probably became infected during the flight; and the remaining passenger probably became infected while in MIQ.

"All 7 passengers were seated in aisle seats within 2 rows of where the presumed index case-patient(s) were seated," de Ligt and his coauthors write. "Combined, these data present a likely scenario of more than 4 SARS-CoV-2 transmission events during a long-haul flight from Dubai to Auckland."

According to de Ligt, there is a chance that some passengers were carrying virus at levels below the limit of detection. "There is also a chance that people got infected after their predeparture test, since many regions in the world have uncontrolled community spread of the virus," he said.

Three of the passengers tested positive on day 3 of their 14-day quarantine period. According to the researchers, this "indicates some of the complexities of determining the value of predeparture testing, including the modality and timing of any such testing," they write. "Although not definitive, these findings underscore the value of considering all international passengers arriving in New Zealand as being potentially infected with SARS-CoV-2, even if predeparture testing was undertaken, social distancing and spacing were followed, and personal protective equipment was used in-flight."

The researchers also note that "the auxiliary power unit of the flight EK448 aircraft was reported as having been inoperative for ≈30 minutes during the 2-hour refueling stop in Kuala Lumpur, such that the environmental control system would not have been working during this period."

Masking Wasn't Mandatory on Flight

Natascha Tuznik, DO, FACP, who was asked to comment on the study, took issue with a phrase in the discussion section of the article, which reads, "These transmission events occurred despite reported in-flight use of masks and gloves."

Dr Natascha Tuznik

"Masking was not mandatory during the flight, which is a big problem," said Tuznik, an infectious disease specialist at the University of California, Davis, School of Medicine, Sacramento, California. "There was also a 2-hour layover in Kuala Lumpur. During that layover, there was a reported problem with the auxiliary power unit for about 30 minutes. It's not surprising that people got infected, because they're not taking the proper precautions and there were circulation issues. The other thing the authors didn't comment on, which is always a concern on these long flights, is the meals. When meals are being served, people are taking their masks off."

In her opinion, the study "reinforces that if you're going to be taking a long flight, you have to consider that your chance of being exposed is going to go up," Tuznik said. "You really need to be vigilant about wearing your mask. If they serve food on the flight, that's something to consider, that you're going to have to take your mask off and that you might be sitting by somebody who's infectious.

"The seating on the plane matters, too. These seven passengers were very close to one another. They say the window seat is probably your best bet, and if you can avoid moving around [during the flight]. It may be difficult to not use the bathroom on a long flight, but that's still a gamble. If you pick a window seat that happens to be right next to a person who's infectious, that's just bad luck; you can't predict that," she said.

The data for the analysis were drawn from a long-haul flight, although de Ligt said tSARS-CoV-2 transmission is possible on shorter flights as well. "More and more studies are coming out, some of them from shorter flights where transmission has been observed," he said. "The important thing to note is that ventilation should be more effective on those shorter flights, and limited movement to bathrooms or for eating should also help reduce the risks."

The study was funded by the New Zealand Ministry of Health, the Ministry of Business, Innovation and Employment, the New Zealand Health Research Council, and the ESR Strategic Innovation Fund. The researchers have disclosed no relevant financial relationships.

Emerg Infect Dis. Published online January 5, 2021. Full text

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