Commercial watercress linked to a parasite outbreak in France
What it found
People who ate raw commercial watercress were far more likely to catch a liver parasite infection.
The link was found during an outbreak investigation among 14 sick people and 23 others in France.
What they found
Studies in people
Raw watercress and infection
Thirteen out of 14 sick people had eaten raw shop-bought watercress, compared with only 3 out of 23 healthy controls. Sick people were much more likely to have eaten it than healthy people.
Watercress soup link
Seven sick people and one healthy person had eaten watercress soup. Once researchers accounted for raw watercress eating, soup alone was no longer linked to the illness.
Other salad leaves
Eating lamb's lettuce, dandelion or fresh mint leaves showed no clear link to the infection when comparing sick people with healthy controls.
Recovery after treatment
All patients were followed up for 6 months. Each fully recovered after taking a single dose of a medicine called triclabendazole at 10 mg per kg of body weight.
Other findings
Contaminated watercress beds
Inspectors traced the watercress eaten by 16 cases back to one producer. One bed had cattle grazing nearby, no flood protection, unexplained water rising from the soil and many snail shells around it.
What the authors conclude
- They say this is the first known outbreak in France tied to commercially grown watercress rather than wild plants.
- They conclude that current rules do not effectively prevent parasite contamination in French watercress production.
- They recommend updating regulations to require protective barriers, regular snail checks and testing snails for the parasite.
How it was done
Five unrelated people in one French town were diagnosed with a liver parasite infection in April 2002. None had eaten wild watercress, so investigators suspected a shop-bought product might be the cause.
Investigators identified 18 confirmed cases of the infection across two districts in northern France. They interviewed 14 of those cases and 23 healthy controls about what uncooked plants they had eaten. They also inspected the watercress beds of the supplier linked to most cases.
What it can’t tell you
- This investigation looked at people who were already sick, so it can show a strong link but cannot prove exactly how each person caught the parasite.
- It also focused on one specific producer in northern France, so the findings may not apply to all watercress sold everywhere.
Who paid
- Authors work at
- Institut de Veille Sanitaire, France
The paper
- Title
- Commercial watercress as an emerging source of fascioliasis in Northern France in 2002: results from an outbreak investigation
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Mailles A, Capek I, Ajana F, Schepens C, Ilef D, Vaillant V (2006). Commercial watercress as an emerging source of fascioliasis in Northern France in 2002: results from an outbreak investigation. Epidemiology and infection. doi:10.1017/S095026880600611XFree full textPubMed 16569267DOI
Summary written 1 Oct 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error