In April 1988, an outbreak of gastroenteritis occurred among employees in a large company in
Helsinki, Finland. A retrospective cohort study, using a self-administered questionnaire, was
carried out to ascertain the cause and extent of the outbreak. To meet the case definition,
employees had to have had diarrhoea and/or vomiting since 2 April, 1998. A subanalysis was
made in the biggest office, consisting of 360 employees, of whom 204 (57%) completed the
questionnaire. Of these 108 (53%) met the case definition. Employees who had eaten raspberry
dressing were more likely to meet the case definition than those who had not (Attack Rate
(AR) 65% versus AR 18% Relative Risk, (RR) 3·7, 95%, Confidence Intervals (CI) 2·0–6·7).
Four stool specimens obtained from affected kitchen staff who had all eaten the raspberry
dressing and who had all become ill simultaneously with the employees were positive by
polymerase chain reaction (PCR) for calicivirus. The data suggest that the primary source of
the outbreak was imported frozen raspberries contaminated by calicivirus.