A rare multiresistant Salmonella
104B has caused an outbreak of 60 microbiologically confirmed cases in May
2005, widely distributed across southern and western Finland. The isolates
have an identical pulsed field gel electrophoresis (PFGE) and antimicrobial
resistance pattern (ACSSuT). Of the 56 cases confirmed so far, 80% were in
females and 45% were in people aged between 15-24 years (range 7 to 53). Before
this outbreak, there were between two and four S.
Copenhagen DT104B cases annually in Finland. None of the previous PFGE types
share exactly the same profile with the isolates in the current outbreak.
A cluster occurred among students of a nursing school in southeast Finland
in mid-May 2005. The nursing school has around 800 healthcare students and
teaching staff. A questionnaire was sent to the students and staff by the
local health authorities. A private company operates the cafeteria providing
lunch at the school. The kitchen had kept frozen food samples from the dishes
served each day, in accordance with the Hazard Analysis Critical Control
Points (HACCP) risk management system . S. Typhimurium DT 104B
was detected in samples of salad made from lettuce, other vegetables and/or
noodles from three successive days, served between 10 and 12 May. Three
salad isolates have been genotyped so far, and are indistinguishable from
the isolates obtained from the patients.
In western Finland, the cases were geographically widespread, but the great
majority of the patients had eaten at the same restaurant on 13 or 14 May.
Between 280 and 570 customers ate at the restaurant on those days. The preliminary
epidemic curve shows that for the restaurant-associated cases, two peaks
occurred on 15 and 18 May 2005, supporting the microbiological and descriptive
epidemiological evidence that the contaminated salad was served in the restaurant
over a three day period (Figure).
Figure. Salmonella Typhimurium var Copenhagen
DT104B, cases by date of first symptoms in Finland, Laboratory of Enteric
Pathogens, KTL (n=43)
A traceback investigation showed that the nursing school and the restaurant
had both purchased iceberg lettuce, the only kind of lettuce served on the
implicated days, with a documented trail leading back to a supplier in Spain.
Thousands of kilograms of this iceberg lettuce have been imported from Spain
and distributed throughout Finland. However, the limited outbreaks observed
to date suggest that only a small proportion of lettuce was contaminated.
The traceback investigation is ongoing. A press release was sent out to
the healthcare settings and environmental authorities on 21 June. An alert
was sent out through the European Early Warning and Response System (EWRS)
on 21 June and the Rapid Alert System for Food and Feed (RASFF) on 22 June