Leeks in cheese sauce linked to food poisoning outbreak
What it found
In a restaurant outbreak in England, people who ate leeks in cheese sauce were far more likely to become ill with diarrhoea and cramps.
Stool samples from two people confirmed the bacterium Clostridium perfringens.
What they found
Studies in people
Leeks in cheese sauce
After adjusting for other foods, people who ate leeks in cheese sauce were about 50 times more likely to become ill than those who did not eat it. This was the only menu item linked to illness.
Symptoms and timing
Of the 28 cases, 27 had diarrhoea and abdominal pain, and 4 reported vomiting. One person was hospitalised. The median time from eating to symptoms was 17 hours.
Stool sample results
Two stool samples from five cases tested positive for Clostridium perfringens. One of these contained the enterotoxin gene, confirming it could cause illness.
Other findings
Food sample results
All food samples taken days later were negative for Clostridium perfringens and other tested germs. The cauliflower cheese had an unsatisfactory aerobic colony count.
Kitchen practices
Investigators found lapses in temperature control during cooking and hot holding, likely cross-contamination between raw and cooked foods, and reuse of leftover cheese sauce the next day. Hot-holding temperatures for vegetable sides were below the recommended 63°C.
Unusual source
A review of foodborne outbreaks in England found that 80% of Clostridium perfringens outbreaks cited red meat or poultry, 4% reported vegetables, and none reported dairy links. This is the first reported instance linked to leeks in cheese sauce.
What the authors conclude
“This study found that this C. perfringens outbreak was associated with the consumption of leeks in cheese sauce; however, the likely vehicle was a contaminated cheese sauce.”
Also in their conclusions
- They conclude that this outbreak of Clostridium perfringens was associated with eating leeks in cheese sauce, but the likely vehicle was a contaminated cheese sauce.
- They advise that food businesses should ensure staff training is updated when menu items or cooking processes change, and that digital temperature recording systems have multiple trained users with correct parameters.
- They recommend that officers investigating similar outbreaks remain open-minded, carry out a full environmental audit early, and gather food samples for testing at the first opportunity.
How it was done
Public health authorities were alerted to 34 reports of diarrhoea and abdominal cramps among people who ate Christmas meals at a restaurant. They investigated to find the source and stop the outbreak.
They recruited 40 people who ate at the restaurant between 7 and 9 December 2018, including 28 who became ill and 12 who did not. They asked about foods eaten and symptoms, visited the restaurant four times, and tested food and stool samples.
What it can’t tell you
- This study cannot prove that the leeks themselves were the source, because no food samples were taken during the period when people were exposed.
- It cannot show whether the leeks or the cheese sauce was the contaminated part, as the two were not tested separately.
- It cannot rule out cross-contamination from other foods or kitchen surfaces as the source of the bacterium.
Who paid
- Conflicts
- None.
- Authors work at
- Shropshire Council, UK; Heart of England NHS Foundation Trust, UK
The paper
- Title
- Outbreak of Clostridium perfringens food poisoning linked to leeks in cheese sauce: an unusual source
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Bhattacharya A, Shantikumar S, Beaufoy D, et al (2020). Outbreak of Clostridium perfringens food poisoning linked to leeks in cheese sauce: an unusual source. Epidemiology and infection. doi:10.1017/S095026882000031XFree full textPubMed 32102705DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error