Strawberries are an important fruit in Belgium both in production and consumption, but little information is available about the presence of Salmonella and STEC in these berries, the risk factors in agricultural production and possible specific mitigation options.
In 2012, a survey was undertaken of three soil and three soilless cultivation systems in Belgium.
No Salmonella spp. was isolated. No STEC was detected in the strawberry samples (0 out of 72), but STEC was detected by qPCR in 11 out of 78 irrigation water and 2 out of 24 substrate samples.
Culture isolates were obtained for 2 out of 11 qPCR positive irrigation water samples and 2 out of 2 substrate samples. Multivariable logistic regression analysis revealed elevated generic E. coli numbers (odds ratio (OR) for 1 log increase being 4.6) as the most important risk factor for STEC, together with the berry picking season (elevated risk in summer).
Presence of generic E. coli in the irrigation water (≥ 1 cfu per 100 ml) was mainly influenced by the type of irrigation water (collected rainfall water stored in ponds was more often contaminated than ground water pumped from boreholes (OR = 5.8)) and the lack of prior treatment (untreated water versus water subjected to sand filtration prior to use (OR = 19.2)).
The follow-up study in 2013 at one of the producers indicated cattle as the most likely source of STEC contamination of the irrigation water.