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.