A multistate outbreak of Escherichia coli O157:H7 infections linked to alfalfa sprouts grown from contaminated seeds.

A multistate outbreak of Escherichia coli O157:H7 infections occurred in the United States in June and July 1997. Two concurrent outbreaks were investigated through independent case-control studies in Michigan and Virginia and by subtyping isolates with pulsed-field gel electrophoresis (PFGE). Isolates from 85 persons were indistinguishable by PFGE. Alfalfa sprouts were the only exposure associated with E. coli O157:H7 infection in both Michigan and Virginia. Seeds used for sprouting were traced back to one common lot harvested in Idaho. New subtyping tools such as PFGE used in this investigation are essential to link isolated infections to a single outbreak.

Outbreak of Legionnaires' disease associated with a display whirlpool spa.

BACKGROUND: Recognized outbreaks of Legionnaires' disease (LD) are rare; when they occur, they provide opportunities to understand the epidemiology of the illness and improve prevention strategies. We investigated a population-based outbreak. METHODS: After the confirmation of LD in October 1996 in five people in neighbouring towns in southwest Virginia, active surveillance for additional cases was undertaken. A case-control study was conducted to identify exposures associated with illness, followed by a cohort study among employees of the facility at which the source of the outbreak was located in order to assess unrecognized exposure and illness. Samples of likely sources of LD in the facility were cultured for LEGIONELLA: RESULTS: In all, 23 laboratory-confirmed cases of LD were eventually identified. Of the 15 cases in the case-control study, 14 (93%) reported visiting a home-improvement store, compared with 12 (27%) of 45 controls (matched odds ratio [MOR] = 23.3; 95% CI : 3-182). Among home-improvement centre patrons, 10 (77%) of 13 cases questioned recalled either visiting or walking by a display whirlpool spa, compared with 3 (25%) of 12 controls (MOR = 5.5; 95% CI : 0.7-256.0). Two cases' sputum isolates were an exact match, by monoclonal antibody subtyping and arbitrarily primed polymerase chain reaction, to a whirlpool spa filter isolate from the store. Employees reporting more exposure to the display spas were more likely to report symptoms of LD or to have an elevated titre. CONCLUSIONS: This investigation shows that LD can be transmitted from a whirlpool spa used for display only, and highlights the need for minimizing the risk of transmission of LD from all water-filled spas. Key messages This paper describes an investigation of a population-based outbreak of Legionnaires' disease (LD). A case-control study first identified a home-improvement store as the likely source of the outbreak. An environmental investigation later confirmed that finding, as two cases' sputum isolates were an exact match, by monoclonal antibody subtyping and arbitrarily primed polymerase chain reaction, to a whirlpool spa filter isolate from the store. The spa was intended and used for display only.