She said: “It was a crazy experience.
“There were 150 people on the flight, and my biggest fear was giving it to them.”
After feeling unwell Ms Fotieo performed a rapid test with a kit she had brought with her which came back positive.
She remained in the toilet for the rest of the journey.
A flight attendant provided her with food and drinks.
Ms Fotieo, who is from Michigan, posted a video on Tiktok from the toilet which has been viewed four million times.
In the video she praised the flight attendant for helping her during the ordeal.
On arrival in Reykjavik, she had to isolate in a Red Cross hotel.
There is a seven-day average of 277,000.
Due to isolation rules, air travel is understaffed with as many as 1,100 cancellations across the USA on Thursday, according to air travel data site FlightAware.