An outbreak of Streptococcus equi subspecies zooepidemicusassociated with consumption of fresh goat cheese

Markku Kuusi,Leila Rantala,Kyosti Siponen,Kaisa Huotari,Marjaana Hakkinen,Maija Hatakka,Veera Gindonis,Anni Virolainen,Elina Lahti,Jaana Vuopio-Varkila,Eija Seuna,Johanna Takkinen,Risto Vuento,Matti Karppelin

doi:10.1186/1471-2334-6-36

Abstract

BackgroundStreptococcus 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.MethodsCases 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).ResultsSeven 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.ConclusionThe 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.

Highlights

Streptococcus equi subspecies zooepidemicus is a rare infection in humans associated with contact with horses or consumption of unpasteurized milk products
In addition to cases notified to National Infectious Disease Register (NIDR), the clinical microbiology laboratories in the country's 21 health care districts were requested to type to species level all group C streptococcal strains isolated from a normally sterile site between September 15 and October 31
S. equi subsp.zooepidemicus was identified after the microbiology laboratories had typed the invasive group C streptococcal isolates further to species level

Summary

Introduction

Streptococcus equi subspecies zooepidemicus is a rare infection in humans associated with contact with horses or consumption of unpasteurized milk products. Zooepidemicus may be found in the nasopharynx, on the tonsils, in the respiratory tract, and on the genital mucous membranes of healthy horses and cattle [2]. It is an important cause of respiratory tract infections in foals and young horses, and it is associated in uterine infections in mares [3]. The source of human infection is often traced back to contact with domestic animals, especially horses, or ingestion of unpasteurized milk or milk products [11]

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