An epidemiological analysis into food poisoning clusters among passengers on two Cathay Pacific Airways flights from Kathmandu to Hong Kong identified beetroot salad as the most likely source of contamination.

The Centre for Health Protection of the Department of Health, Hong Kong, released its findings on Friday.

Based on the investigation results, the department “did not rule out that the food poisoning” clusters on flight CX640 were caused by beetroot salad contaminated with Staphylococcus aureus served on board.

The investigation revealed that a total of 43 passengers (22 men and 21 women) on the flights, which arrived in Hong Kong on January 8 and 9, developed symptoms of food poisoning such as vomiting, nausea, abdominal pain, and diarrhoea approximately 10 to 60 minutes after consuming inflight meals.

The affected persons ranged in age from 11 to 75, and none required hospitalisation.

“Stool samples from two patients tested positive for Staphylococcus aureus,” stated the press release issued by Hong Kong’s Department of Health. “The overall clinical symptoms and incubation period of the affected persons were compatible with food poisoning caused by Staphylococcus aureus.”

The department successfully contacted 120 passengers on board the affected flights through face-to-face interviews, telephone calls, emails, and a hotline to conduct a comprehensive epidemiological investigation.

To trace the cause of the incident, the department also conducted a detailed assessment of the reported symptoms on board the flights and the food consumed both on board and before boarding.

The investigation confirmed that all 43 affected passengers had consumed food served on board the aircraft and had not eaten any other common food before boarding.

“Based on the case-control study analysis, the beetroot salad served on board was the only food item statistically significantly associated with developing disease, suggesting that the consumption of beetroot salad was a risk factor for the illness,” the statement read.

Out of approximately 500 servings of food supplied on the two flights, the department collected two samples of food (including two samples of beetroot salad) from the same batches left undistributed on the two aircraft. The test results indicated that Staphylococcus aureus levels did not exceed the food safety standard.

During the investigation, the department found that the beetroot salad had been supplied exclusively to Cathay Pacific flights from Kathmandu to Hong Kong since January.

Department staff inspected the food factory twice and discovered that the preparation of the beetroot salad involved several manual handling steps, which might have increased the risk of contamination with Staphylococcus aureus.

On January 10, the department instructed the food factory to cease supplying the beetroot salad. Since then, there have been no reports of food poisoning on related flights.

To mitigate risks, the department recommended that the food factory minimise manual handling during food preparation processes and use utensils and equipment to avoid direct hand contact with food ingredients as much as possible.

Additionally, all food handlers must strictly adhere to hand hygiene guidelines, especially during food preparation steps involving manual handling without subsequent heating processes.