If one takes the flight XXX ->YYY->ZZZ, with a layover at YYY where one left the airport, does airport XXX or YYY count as the 1st embarkation point?

Question

https://www.iatatravelcentre.com/world.php -> United States indicates:

2. Passengers entering or transiting through the USA must have a negative COVID-19 test taken at most 3 days before departure from the first embarkation point. Tests accepted are: antigen, NAAT, RT-LAMP, RT-PCR or TMA. Passengers details (e.g., name and date of birth) in the certificate must match those stated in the passport or other travel document; and the test result must specify "negative" or "not detected". If marked "invalid" it is not accepted.

If one takes the flight: airport XXX (not in the US) -> airport YYY (not in the US) -> airport ZZZ (in the US), with a layover at YYY during which one left the airport and reentered it, does airport XXX or airport YYY count as the first embarkation point? The purpose of defining the first embarkation point is satisfying the covid-19 requirements.

Assume that:

• airport XXX and airport YYY are in 2 different countries,
• the layover at airport YYY lasts less than 24 hours,
• the flight XXX ->YYY->ZZZ is on a single ticket,
• no checked baggage will be retrieved and re-checked at airport YYY: all baggage are checked at airport XXX through to the final destination (airport ZZZ),

in case this changes the answer.

Answer 1

CDC tells us:

If I have one or more connecting flights to the US, does the 3-day period apply to the first flight or the last one? Do I need to get another test if I have a connecting flight?

If your itinerary has you arriving to the US via one or more connecting flights, your test can be taken within the 3 days before the departure of the first flight.

If the 3-day testing period expires before one of your connecting flights, you only need to get retested before boarding connecting flights if:

• You planned an itinerary incorporating one or more overnight stays en route to the US. (NOTE: You do not need to be retested if the itinerary requires an overnight connection because of limitations in flight availability.), OR
• The connecting flight is delayed past the 3-day limit of testing due to a situation outside of your control (e.g., delays because of severe weather or aircraft mechanical problem), and that delay is more than 48 hours past the 3-day limit for testing.

So it depends on whether "the itinerary requires an overnight connection because of limitations in flight availability".

Note also that they count it as 3 days, not 72 hours. So for your second flight departure, even if that is considered as the point of departure, any test taken in the 3 days before that flight, even very early in the morning, is valid. Of course timezones may play for or against you :-)