Epidemiology and Infection

Febrile gastroenteritis after eating on-farm manufactured fresh cheese – an outbreak of listeriosis?

a1 Department of Epidemiology, Swedish Institute for Infectious Disease Control, SE-17182 Solna, Sweden
a2 European Programme for Intervention Epidemiology Training (EPIET)
a3 Gaevleborg County Office for Infectious Disease Control, Landstinget Gaevleborg, SE-80187 Gaevle, Sweden
a4 Section of Infectious Diseases, Department of Medical Sciences, Uppsala University Hospital, SE-75185 Uppsala, Sweden
a5 Department of Food Hygiene, Faculty of Veterinary Medicine, SLU, P.O. Box 7009, SE-75007 Uppsala, Sweden
a6 Karolinska Hospital, Department of Clinical Microbiology, SE-17176 Stockholm, Sweden
a7 Section of Veterinary Service and Food Control, Gaevleborg Administrative Board, SE-80170 Gaevle, Sweden
a8 Department of Bacteriology, National Veterinary Institute, SE-75189 Uppsala, Sweden


An outbreak of febrile gastroenteritis affected consumers of on-farm manufactured dairy products from a summer farm in Sweden. Symptoms included diarrhoea, fever, stomach cramps and vomiting in 88, 60, 54 and 21% of cases identified. The median incubation period was 31 h. A cohort study with 33 consumers showed an attack rate of 52% and an association between the total amount of product eaten and illness (P=0·07). Twenty-seven of 32 (84%) stool samples cultured for Listeria monocytogenes tested positive, although there was no association between clinical disease and the isolation of L. monocytogenes. In addition, gene sequences for VTEC and ETEC were detected in 6 and 1 subjects, respectively. Bacteriological analysis of cheese samples revealed heavy contamination with L. monocytogenes and coagulase positive staphylococci in all of them and gene markers for VTEC in one of them. Molecular profiles for L. monocytogenes isolated from dairy products, stool samples and an abscess from 1 patient who developed septic arthritis were identical. Results of both microbiological and epidemiological analyses point to L. monocytogenes as the most likely cause of this outbreak. The finding of markers for VTEC in some humans and cheese samples means that a mixed aetiology at least in some cases cannot be conclusively ruled out.

(Accepted October 3 2002)

c1 Ecology & Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.