This study set out to evaluate the microbiological hazards associated with the foods served on aircraft. To identify the microbiological quality of hot and cold meals prepared worldwide, samples of aircraft meals were monitored for Salmonella between 1989 and 1994, and for indicator bacteria and Staphylococcus aureus, Bacillus cereus and Clostridium perfringens between 1991 and 1994. Additionally, a Salmonella outbreak among air passengers was investigated to evaluate risk factors for the contamination and growth of Salmonella in aircraft meals. In order to find out about the carriage of S. aureus among flight catering employees, hand and nasal samples were taken and the carriage was further monitored by characterising the enterotoxicity and the macrorestriction patterns of the bacterial strains.
The monitoring of hot and cold meals revealed Salmonella in 7 (0.3%) out of 2299 hot meal samples, but in only one (0.1%) out of 1576 cold meal samples. Although Salmonella was found in cold meals only once, this finding of Salmonella enterica serovar Ohio was subsequently linked to a foodborne outbreak among air passengers on a flight from Bangkok to Helsinki in 1990. There was no evidence that any of the Salmonella positive hot meals had caused any outbreaks. Many of the hot and cold meals also exceeded the microbiological standards of the Association of European Airlines (AEA) for Escherichia coli (8.2% and 14%, respectively), S. aureus (0.6% and 7%, respectively) and B. cereus (0.7% and 3%, respectively). The contamination rate by these bacteria was thus considerably higher in cold meals than in hot meals. The final re-heating of hot meals on board is likely to reduce the microbial risk associated with foodborne pathogens because heating food affects the viability of the bacteria. Significant differences were detected in the microbiological quality of the meals depending on the meal preparing country.
A widespread outbreak caused by Salmonella enterica serovar Infantis via food prepared in a flight kitchen was investigated. Of those infected, 91 were air passengers on a charter flight from Helsinki to Rhodes, 107 were railway passengers and 28 were flight kitchen employees, including 23 food handlers. The majority of the food handlers (17) were symptom-free carriers and six of them had mild diarrhoea. Widespread contamination of the production of the flight kitchen followed which led to an outbreak of Salmonella . The source of infection was traced to the following foods: egg sandwiches served on trains, the aircraft meals served on that particular flight to Rhodes and cold cuts served to the catering staff during breakfast. S. Infantis was found in a hot dish that represented the batch served on the flight to Rhodes. The most prominent factor relating to food contamination was that food handlers suffering from mild diarrhoea were not excluded from work, and there was no hygiene education either. A heat wave combined with a shortage of refrigeration facilities and the possible malfunction of the re-heating oven on board contributed to the multiplication of Salmonella . After the outbreak, the company employed a food hygienist responsible for food hygiene expertise, such as the implementation of quality assurance system and hygiene education of food handlers.
The study of the carriage of S. aureus among flight catering employees showed a remarkable prevalence of enterotoxic S. aureus in hand and nasal samples, 6% and 12% respectively. Nasal carriers can easily transmit S. aureus onto the hands, which means a potential risk of food poisoning if the strain is producing enterotoxin. Nasal sampling was shown to be a better way of detecting S. aureus carriers than hand sampling. PFGE macrorestriction profiles revealed a total of 32 different types associated with the 35 employees carrying S. aureus , thus indicating great diversity. Molecular characterisation of isolates is of great value, especially if there is a need to trace the contamination source. It also revealed that some food handlers carried more than one clone. Testing food handlers working in high-risk premises such as flight kitchens, provides valuable information about carriers and helps in planning preventive measures.
The production of aircraft meals is a high-risk mass catering operation that has global dimensions. Microbiological hazards are the most prominent risk factors connected with this kind of food production. They arise owing to the complexity of the operation in the flight kitchen, long food production chains and on board service with limited facilities. Therefore, strict quality assurance based on the hazard analysis critical control point (HACCP) system should be applied by the flight caterers and the expertise of the official food control authorities should also meet the requirements of this special catering branch.