Livsmedelsverket said 3% of the beef samples contained STEC positive for stx2 and eae, which are important markers for the ability of the bacteria to cause severe disease.
In total, 27 STEC were isolated from 177 samples, belonging to 14 different serogroups. STEC O26 was most common (2% of the beef samples).
STEC O157, frequently implicated in STEC-related foodborne outbreaks, was found in two (1%).
There are between 300-400 reported STEC E.coli cases, of which around half are domestic, in Sweden each year.
Investigate prevalence
Mats Lindblad, communicable disease coordinator at Livsmedelsverket, said the reason for the study was to investigate the prevalence of ESBL-producing E.coli.
“The prevalence rate was higher than expected but we worked a lot with the samples and studied the isolates with different methods," he told FoodQualityNews.
“We will use the findings to emphasize how to cook, such as medium-rare hamburgers for example, to emphasize the advice we are already giving.
“The positive thing was that we didn’t find any in vegetables but Salmonella is more probable than STEC in this food.
“We would like to look at Swedish meat next, as we didn’t do that in this study, and then we could make some comparisons which could be interesting.”
The samples were made up of 39 from Ireland, 96 from other countries and 42 from South America.
They were collected at retail stores, importers, outlets and in markets. Samples of minced or whole meat from cattle were picked up fresh or frozen from 2010 to 2011.
Beef sample collection included products from the most common exporters to the country.
Detection of virulence genes (stx1, stx2, eae) and genes specific for different serogroups (O26, O103, O111, O145 and O157) was performed by real-time PCR.
This was followed by isolation of bacteria from the stx-positive enriched samples by use of immunomagnetic separation. STEC bacteria were also isolated by an immunoblotting method.
No findings in leafy greens
The study also investigated STEC in leafy greens for 630 samples on the Swedish market.
The enrichment broth of 11 (2%) of the samples from leafy greens were tested positive for stx1 and/or stx2 by PCR analysis; however, no bacteria were isolated.
Presumptive STEC was detected in enriched samples from domestic and imported products.
E. coli was found in 68 (39%) out of 174 and 14 (30%) out of 46 samples of imported and Swedish leafy greens, respectively, indicating the proportion of stx-positive E. coli in the samples was low.
Collection of leafy greens consisted of domestic and imported products on the market from 2012 to 2013.
The agency said new data was required to assess the public health risk of STEC in food, which could be used for developing risk management strategies.