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Open Access Research article

An outbreak of Streptococcus equi subspecies zooepidemicus associated with consumption of fresh goat cheese

Markku Kuusi1*, Elina Lahti2, Anni Virolainen3, Maija Hatakka4, Risto Vuento5, Leila Rantala2, Jaana Vuopio-Varkila3, Eija Seuna2, Matti Karppelin6, Marjaana Hakkinen2, Johanna Takkinen1, Veera Gindonis2, Kyosti Siponen4 and Kaisa Huotari1

Author Affiliations

1 National Public Health Institute (KTL), Department of Infectious Disease Epidemiology, Helsinki, Finland

2 National Veterinary and Food Research Institute (EELA), Helsinki, Finland

3 National Public Health Institute (KTL), Department of Microbiology, Helsinki, Finland

4 National Food Agency, Helsinki, Finland

5 Tampere University Central Hospital, Centre for Laboratory Medicine, Tampere, Finland

6 Tampere University Central Hospital, Department of Medicine, Tampere, Finland

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BMC Infectious Diseases 2006, 6:36  doi:10.1186/1471-2334-6-36

Published: 27 February 2006

Abstract

Background

Streptococcus equi subspecies zooepidemicus is a rare infection in humans associated with contact with horses or consumption of unpasteurized milk products. On October 23, 2003, the National Public Health Institute was alerted that within one week three persons had been admitted to Tampere University Central Hospital (TaYS) because of S. equi subsp. zooepidemicus septicaemia. All had consumed fresh goat cheese produced in a small-scale dairy located on a farm. We conducted an investigation to determine the source and the extent of the outbreak.

Methods

Cases were identified from the National Infectious Disease Register. Cases were persons with S. equi subsp. zooepidemicus isolated from a normally sterile site who had illness onset 15.9-31.10.2003. All cases were telephone interviewed by using a standard questionnaire and clinical information was extracted from patient charts. Environmental and food specimens included throat swabs from two persons working in the dairy, milk from goats and raw milk tank, cheeses made of unpasteurized milk, vaginal samples of goats, and borehole well water. The isolates were characterized by ribotyping and pulsed-field gel electrophoresis (PFGE).

Results

Seven persons met the case definition; six had septicaemia and one had purulent arthritis. Five were women; the median age was 70 years (range 54–93). None of the cases were immunocompromized and none died. Six cases were identified in TaYS, and one in another university hospital in southern Finland. All had eaten goat cheese produced on the implicated farm. S. equi subsp. zooepidemicus was isolated from throat swabs, fresh goat cheese, milk tank, and vaginal samples of one goat. All human and environmental strains were indistinguishable by ribotyping and PFGE.

Conclusion

The outbreak was caused by goat cheese produced from unpasteurized milk. Outbreaks caused by S. equi subsp. zooepidemicus may not be detected if streptococcal strains are only typed to the group level. S. equi subsp. zooepidemicus may be a re-emerging disease if unpasteurized milk is increasingly used for food production. Facilities using unpasteurized milk should be carefully monitored to prevent this type of outbreaks.