- Several passengers fell ill on two separate flights from Guam to Tokyo.
- Local news reported they were all students and teachers from the same high school.
- Some felt ill before boarding, suggesting it wasn't caused by the airlines' inflight meals.
Dozens of passengers fell ill with symptoms of food poisoning on United Airlines and Japan Airlines flights last Thursday.
Both flights were traveling from Guam, an island in the western Pacific Ocean, to Tokyo Narita Airport.
The Japanese national broadcaster NHK reported the illness affected 27 students and teachers from the same high school traveling across both flights. It added that their symptoms included vomiting and fevers.
In a statement shared with Business Insider, United said that "several customers showed signs of possible food poisoning."
It added that it activated its "in-flight medical service" before landing and worked with Tokyo health authorities on arrival.
Japan Airlines told BI that 16 passengers traveling together fell ill on Flight 942. The airline added that their illnesses weren't caused by its inflight meals.
Six of them had stomach pains and other symptoms before boarding, while nine felt ill after takeoff and another one after landing, it added.
In a similar incident earlier this year, United Airlines had to briefly ground a jet for deep cleaning.
A group of passengers fell ill with symptoms such as vomiting, although as they were all returning from the same cruise, it appeared similarly not to have been caused by inflight meals.
Airlines have strict and thorough cleaning processes to avoid incidents of mass illness.
Perhaps the most infamous one took place on a Japan Airlines flight in 1975, when 197 people fell ill after some of the meals were believed to be contaminated by Staphylococcus bacteria, which caused food poisoning.