Health officials said on Friday that they could not rule out that beetroot salad contaminated with a bacterium served on board was responsible for the suspected food poisoning suffered by dozens of passengers of two Cathay Pacific flights arriving from Nepal this month.

The Centre for Health Protection (CHP) said its investigation found that 43 passengers, aged between 11 and 75, developed food poisoning symptoms such as vomiting, nausea, abdominal pain and diarrhoea, about 10 to 60 minutes after having meals on the CX640 flights from Kathmandul on January 8 and 9.

None of the passengers had to be taken to hospital, the CHP said.

"Stool samples from two patients tested positive for Staphylococcus aureus. The overall clinical symptoms and incubation period of the affected persons were compatible with food poisoning caused by Staphylococcus aureus," the centre said in a statement.

It added that the beetroot salad was the only food served on board that was likely to have caused such poisoning, from a statistical standpoint.

However, tests on samples taken from the aircraft showed the level of Staphylococcus aureus in the salad did not exceed food safety standards.

The CHP said the food was supplied exclusively to Cathay for its flights from Kathmandu since the start of the month and the factory concerned was later asked to stop providing it. Inspections of the factory found the way the food was being handled might have increased the risk of contamination.

In response, Cathay acknowledged the findings but stressed that no signs of contamination were found in the samples it checked in its own lab.

"Cathay Pacific confirms that this salad is not served on any of our other flights. Aside from these two cases, there have not been any similar instances of customers experiencing symptoms of suspected food poisoning on any of our recent flights," it said in a statement.

The airline apologised again to passengers affected and added that it has reinforced food-handling processes and staff training on hygiene.