Clostridium perfringens and Salmonella were the agents responsible for the most foodborne outbreaks in Singapore from 2018 to 2021, according to a study.

A total of 171 outbreaks involving 7,538 cases were investigated from January 2018 to December 2021. The number of outbreaks ranged from 12 in 2020 to 59 in 2019.

For the 121 foodborne outbreaks, more than 42 percent were traced to food prepared by caterers, 14.9 percent by restaurants, and 12.4 percent by in-house kitchens. Of the 50 non-foodborne outbreaks, 48 were at schools, found the study published in the International Journal of Environmental Research and Public Health.

The Singapore Food Agency (SFA) and Ministry of Health, together with other relevant public agencies, conduct outbreak investigations.

Stool samples of 1,050 patients were collected for laboratory identification of causative pathogens. A total of 1,024 food samples were seleced for microbiological analysis based on the food consumption history of cases and epidemiological information from outbreaks, while 917 environmental swabs were taken based on kitchen operations via interviews with food handlers.

Data on pathogens
Clostridium perfringens with 20 and Salmonella with 18 outbreaks were the most common pathogens. Salmonella outbreaks involved Salmonella Enteritidis, Weltevreden, Typhimurium, and Salmonella Kirkee. Other causative pathogens included E. coli, Vibrio parahaemolyticus, Bacillus cereus, and Staphylococcus aureus.

Food samples and environmental swabs collected were mostly positive for Bacillus cereus. only 100 of the 1,024 food samples were positive. The top 3 bacterial pathogens were Bacillus cereus, Staphylococcus aureus, and E. coli. In total, 17.3 percent of food samples had more than one type of pathogen.

only 134 of 917 environmental swabs collected were positive for pathogens. The top three were Bacillus cereus, norovirus, and Salmonella Enteritidis.

Bacillus cereus was detected in a variety of food samples such as ready-to-eat fish, chicken, milk powder, vegetables, rice, noodles, and sauces and environmental swabs including on a knife, chopping board, utensils, preparation table, door handle, and kitchen appliances.

It is important to ensure good temperature control, proper food handling practices, and the routine disinfection of food contact surfaces during food preparation, as once food is contaminated, cooking may kill the bacteria but not remove the toxins produced, said scientists.

COVID impact and caterers role
based on national disease surveillance statistics for Singapore, there was an increase in the number of food poisoning notifications from 4.8 to 7.5 per 100,000 population from 2013 to 2019. In 2020 and 2021, notifications decreased to 3.9 and 4.7 per 100,000 population, respectively. Similar reductions were observed in other countries, likely due to COVID-19 control measures.

The relaxation of Coronavirus measures, such as the gradual reopening of schools, workplaces, and food establishments for dining-in, saw the number of outbreaks climb in 2021.

A large proportion of outbreaks could be attributed to transmission from food prepared by licensed caterers for events and gatherings and dining in at restaurants. While caterers were linked to 51 outbreaks, unlicensed premises and home-based businesses both caused two each.

Common foods associated with Clostridium perfringens include meat, poultry products, soups, sauces such as gravy, and other precooked food and are typically associated with improper cooking or the inadequate heating of products. Caterers usually have to cook in bulk to serve larger groups of customers, and it is crucial for them to rapidly cool food products, said scientists.

In outbreaks were the causative agents could not be determined, many had findings of poor personal hygiene, environmental hygiene and/or poor food preparation practices.

“Mitigation measures such as implementing stricter food hygiene protocols and the re-training of food handlers would help to improve overall food hygiene and handling standards and consequently reduce the number of pathogens found in food and the environment. This would ultimately reduce the risk of gastroenteritis outbreaks in Singapore.”