Large outbreak of Salmonella enterica serotype paratyphi B infection caused by a goats' milk cheese, France, 1993: a case finding and epidemiological study

Abstract

Objective: To assess the magnitude of a nationwide outbreak of infection with Salmonella enterica serotype paratyphi B and identify the vehicle and source of infection.

Design: A case finding study of S paratyphi B infection between 15 August and 30 November 1993; a pair matched case-control study; an environmental investigation at a processing plant that produced a raw goats' milk cheese incriminated in the outbreak; phage typing and genotyping of food and human S paratyphi B isolates.

Setting: France, 15 August to 30 November 1993.

Subjects: 273 patients with S paratyphi B infection; 59 pairs of cases and controls matched for age, sex, and city of residence.

Main outcome measures: Numbers of cases and incidence rates by region of residence and age; matched odds ratios for dairy food preferences.

Results: Among the 273 cases there was one death; 203 (78%) strains belonged to phage type 1 var 3. The incidence of infection was greatest in the region where goats' milk cheese is commonly produced. Comparison of cases and controls showed a 12-fold greater risk of illness (95% confidence interval 1.6 to 92.3) from eating brand A unpasteurised goats' milk cheese. S paratyphi B isolates of phage type 1 var 3 were recovered from cheese A, goats' milk at the plant processing cheese A, and goats' milk supplied to the plant by a single farm. Genotypic IS 200 typing of food and human 1 var 3 phage type isolates showed a common IS 200 pattern.

Conclusion: This outbreak emphasises the potential health hazards of widely distributed unpasteurised milk products in France and the need for their close bacterial monitoring.