Human listeriosis in Denmark 1981-1987 including an outbreak November 1985-March 1987.

Clinical manifestations, predisposing factors and outcome of listeriosis in Denmark during the period 1981-1987 are described. An increased incidence of the disease during the period November 1985-March 1987 was due mainly to 35 patients infected with strains of Listeria monocytogenes indistinguishable by phage-typing. These patients were younger, previously healthier and had a better prognosis. Also, there were more cases in pregnant women and neonates than in other persons. A strong correlation was found between predisposing factors and mortality. We conclude that there was an outbreak caused by a single source of infection and which was distributed all over the country. It lasted for more than a year and affected most categories of people. The source was not identified.