1st US airline offers rapid COVID-19 testing to some passengers

Jul 27, 2020
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In order to get a positive test for the virus, enough of it must be forming in an infected person at the time of assay. This can actually take a number of days after infection. You have the disease, but for days can test negative (1). If one were on a very long flight, say 15 hours, it is possible that they could test negative at the start of the flight, and test positive at the end, if they are on the verge of "crossing-over" : negative-to-positive when they boarded the flight. It would largely depend on the rate of viral replication in a given individual.

Looking up the "longest commercial airline flight", it came back as:

"Singapore Airlines' direct flight from Singapore to Newark, New Jersey, is currently the longest flight in the world, lasting around 18 hours and 30 minutes and traveling 9,534 miles."

People using such long fights, lasting many hours, certainly run a risk (likely slight), of contracting the disease even if all people tested negative minutes before wheels-up. The actual risk would be variable depending on the origin of the flight and all those aboard, the number of people on board, and other mitigating or exacerbating factors.

Best solution: Don't take long flights.

The longer the flight, the greater the risk. In some infected passengers who later who may end up in the ER, the virus could multiply at an exponential rate, meaning the carrier could become infective half way though an 18 hour flight. While this seems fanciful, this virus is so strange that until proven otherwise, many experts would agree that it is real possibility. Once an individual tests positive, they could easily become infective within hours. On a long flight, that could be many hours of increasing exposure as the virus replicates.

(1) https://medical.mit.edu/covid-19-updates/2020/07/when-should-i-be-tested
 
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Sep 24, 2020
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Fortunately the cabin air is constantly refreshed with outside air. The entire passenger air supply is replaced every three minutes or so.
 
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Jul 27, 2020
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Fortunately the cabin air is constantly refreshed with outside air. The entire passenger air supply is replaced every three minutes or so.
This is true. But contact surfaces are not "refreshed", and an infected passenger could contaminate various surfaces to spread the virus.

The biggest issues would be 1) proximity to an infected person, (2) rate of viral shedding, and (3) direction of air flow carrying any invective aerosols, and (4) contaminated surfaces.
 
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Jul 27, 2020
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Fortunately the cabin air is constantly refreshed with outside air. The entire passenger air supply is replaced every three minutes or so.
Reading through the article again, a part of the screening process could leave a big hole in its reliability. Quoting from the story:

"Travelers who opt for a mail-in test will receive a nasal swab self-collection kit from the testing company Color, and are recommended to return their samples within 72 hours of their trip. Color will provide test results via text or email within 24 to 48 hours."

End quote

This means you can return a swab for assay 72 hours before boarding (and obtaining a negative test). This provides at least three days for an infected passenger to ramp up production of the virus before their flight.

In a worse-case scenario, an infected person could take their swab sample 3-4 days after being infected (but before a "positive" viral load appears), and send it off up to 3 days before the flight. They get a negative result the day before the flight from the 3-day post-infection sample, meaning they are getting clearance 6 days after they were infected. Unless you run another test just prior to boarding, such a person could already be a super-spreader but would not know this due to the time lag from infection to positive assay, and be a possible threat for viral spread (assuming they are asymptomatic at the time of boarding.)

It would seem that very accurate testing just before boarding would be optimal, limiting the time frame for an active infection to be shedding virions while in flight.
 
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