Late yesterday the CDC updated its requirement for COVID testing to include all arrivals in to the US. It has previously only covered passengers from the UK. Full details can be read using this link.
Key wording is as follows:
If you plan to travel internationally, you will need to get tested no more than 3 days before you travel by air into the United States (US) and show your negative result to the airline before you board your flight, or be prepared to show documentation of recovery (proof of a recent positive viral test and a letter from your healthcare provider or a public health official stating that you were cleared to travel).
On January 12, 2021, CDC issued an Order requiring all air passengers arriving to the US from a foreign country to get tested no more than 3 days before their flight departs and to present the negative result or documentation of having recovered from COVID-19 to the airline before boarding the flight. Air passengers will also be required to confirm that the information they present is true in the form of an attestation. This Order is effective as of 12:01am EST (5:01am GMT) on January 26, 2021.
The order goes live in about 7 hours.