Source of watercress contamination which sickened 19 remains unclear
FSA’s investigations identified the supplier and watercress farms that provided the product to Sainsbury’s during August 2013.
The unnamed supplier sourced watercress for Sainsbury’s from 10 farms in southern England.
However, investigations on the watercress farms are ongoing and the source contamination is currently unclear.
Between 30 August and 19 September, 19 cases of STEC O157 were reported with 14 in England, four in Wales and one in Scotland.
Seven cases were hospitalised out of the 19 and 13 were interviewed, with 10 saying that they consuming watercress purchased from one retailer.
From 2 September, 12 cases were reported, compared with around one to two cases per week in the previous months.
Sainsbury’s recall
Sainsbury’s recalled six pre-packed bagged salads containing watercress on 12 September.
The products were Watercress Leaves (75g), Watercress, Spinach and Rocket salad (100g) Watercress, Spinach and Rocket (170g), Watercress twin pack (2 x 35g), So Organic Watercress (75g) and So Organic Watercress, Spinach and Rocket (100g).
The latest date of onset in this outbreak was 29 August suggesting that the outbreak is over, said the report.
Unclear contamination source
Samples of watercress from the field and following processing, environmental samples, have been taken by enforcement authorities at Supplier A’s premises to pinpoint the cause of the contamination.
Possible routes of contamination include a failure in control measures protecting the watercress from agricultural run-off, contamination of water or growing materials used in production or contaminated watercress seeds.
Primary cases had an unusual demography for cases of STEC infection: predominantly female (11/17) with a median age of 65 years (range: 4–87), compared to the usual high incidence of cases in children under the age of four.
STEC O157 phage type 2 is the fourth most common STEC phage type reported in England, with an average of 44 cases reported per year between 2009 and 2012, with a peak of cases in summer.
Source: Eurosurveillance, Volume 18, Issue 44, 31 October 2013
Authors: N Launders, L Byrne, N Adams, K Glen, C Jenkins, D Tubin-Delic, M Locking, C Williams, D Morgan, on behalf of the Outbreak Control Team
