Dozens of pupils and three teachers from a British school were rushed to hospital in the US after the outbreak of a "virulent" stomach bug.
The party from Crookhorn College in Waterlooville, Hampshire, were in Washington DC when ambulances were called to Hotel Harrington on Sunday.
One parent told the BBC her daughter showed symptoms after eating at a branch of Planet Hollywood in New York.
The restaurant said it did not believe it was the cause of the mass sickness.
The group is expected to land in the UK on Wednesday.
In total, 48 children and three teachers were treated, with 13 found to be suffering "gastrointestinal distress".
The rest were treated as a precaution, according to the District of Columbia Fire and EMS.
The Department of Health, Washington, DC said it was "investigating this outbreak of illness".
Parent Susan Crowle said her 16-year-old daughter Nicola was the first pupil to fall ill shortly after the group arrived in New York.
Two days later, other students also started to feel poorly, she said.
The only meal Nicola had eaten during the trip was at Planet Hollywood on the first day, Ms Crowle said.
Nicola had been admitted to hospital with stomach problems, where she spent two nights before being discharged.
Ms Crowle said her daughter then tried to "sleep off" the illness on the coach trip to Washington, but collapsed when she arrived and was again admitted to hospital as other students started to fall ill.
She added that Nicola's condition was improving and she expected to make the flight back to the UK with her fellow pupils.
Update multiple sick people Harrington Hotel. #DCsBravest transported a final total of 48 Juveniles and 3 adults. That includes those previously transported. Some of those have no symptoms but are being tx as a precaution. We utilized our ambulance buses in this process. pic.twitter.com/DQ3vx66uO2— DC Fire and EMS (@dcfireems) April 2, 2018
In a statement, the school confirmed a "virulent gastro virus" had affected "most" of those attending the six-night trip, which had started in New York on Wednesday.
It said an additional member of staff had flown to Washington DC to provide "further support to the students".
Two students remained in hospital on Tuesday, the school said.
It praised school staff in the US for doing "the most amazing job at looking after the children" adding its main priority was "to ensure that all the students and staff get home safe and well".
Jackie Branson, chair of governors at the school, said all students were expected to be able to fly back to the UK later.
She added that Public Health England had been informed.
In a statement, Planet Hollywood said: "As the rest of the group became sick 48 hours after their visit, we can pretty safely assume that it is extremely unlikely that Planet Hollywood was involved."
It added other groups who were at the restaurant "on the same evening, at the same time, reported no issues".