In October 2009 an outbreak of a foodborne microsporidia occurred among 135 persons hotel guests and staff in Varmland County, Sweden. Enterocytozoon bieneusi was identified in stool samples submitted by 7 of 11 patients. A restropective cohort study was conducted. A case-patient was defined as a person who ate at the hotel on October 23, 2009 and subsequently develped at least one of the following symptoms: diarrhea, vomiting, abdominal pain or nausea. An onset date was also required.

In total, 450/525 (86%) persons completed the questionnaire and 135 met the case definition (Attributable Risk 30%). The median age of case patients was 52 years (range 20-65 years) and most (86%) were female. These figures were similar to those of the cohort as a whole (median age 52 years, 84% female). Onset dates ranged from October 23 to November 13. The median incubation was 9 days. The most common symptoms were abdominal pain (87%), diarrhea (82%), and nausea (82%). Median duration of illness was 6 days (range 1-20 days).

Consumption of cheese sandwiches [Relative Risk (RR) 4.1, 95% Confidence Interval (CI) 1.4-12.2], salad (RR 2.1, 95% CI 1.1-4.0), and mashed potatoes (RR 2.09, 95% CI .99-4.41) were associated with illness in univariate analysis. In multivariate analysis only the cheese sandwich and the salad continued to show a significant association with illness: the Odds Ratio (OR) for the cheese sandwich was the highest at 6.57 (95% CI 1.53-28.28, P=0.011) while the OR for salad was 2.49 (95% CI 1.12-5.54, P=0.026). Both of these items contained cucumber slices.

Investigators found that washed, pre-sliced cucumbers sealed in plastic bags and imported from Spain were used in both the cheese sandwiches and the salad. Because the pre-sliced cucumbers were not processed further at the hotel, investigators hypothesized that contamination occured before harvest, either by contaminated manure, manure compost, sewage sludge, irrigation water, runoff water from livestock operations or directly from wild and domestic animals. The cucumbers could not be traced back to the farm.