An outbreak of Listeria monocytogenes serotype 3a infections from butter in Finland

In February 1999, an outbreak of listeriosis caused by Listeria monocytogen es serotype 3a occurred in Finland, All isolates were identical, The outbre ak strain was first isolated in 1997 in dairy butter. This dairy began deli very to a tertiary care hospital (TCH) in June 1998, From June 1998 to Apri l 1999, 25 case patients were identified (20 with sepsis, 4 with meningitis , and 1 with abscess; 6 patients died). Patients with the outbreak strain w ere more likely to have been admitted to the TCH than were patients with ot her strains of L. monocytogenes (60% vs. 8%; odds ratio, 17.3; 95% confiden ce interval, 2.8-136.8), Case patients admitted to the TCH had been hospita lized longer before cultures tested positive than had matched controls (med ian, 31 vs. 10 days; P = .008), An investigation found the outbreak strain in packaged butter served at the TCH and at the source dairy, Recall of the product ended the outbreak.