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Public Health - Seattle & King County


Listeriosis is an infection caused by the bacteria Listeria monocytogenes. Persons at increased risk for severe infections include immunocompromised persons, the elderly, pregnant women, and newborn infants. The bacterium is unusual among foodborne pathogens in that it multiplies at low temperatures, including in refrigerated foods. Transmission occurs primarily through ingestion of contaminated drinks and foods, including raw (unpasteurized) or contaminated milk, soft cheeses such as queso fresco, vegetables, and ready-to-eat meats. During pregnancy, infection can lead to spontaneous abortion, stillbirth, or premature birth. Transmission during delivery can cause severe, often fatal, infections in the newborn, even if the mother is asymptomatic.

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Listeriosis in King County

Purpose of surveillance:

  • To identify common source outbreaks
  • To identify and eliminate sources of transmission, including contaminated food products

Listeriosis case reports

Local epidemiology:

In 2012, ten cases of listeriosis were reported in King County. Of these cases, eight (80%) were hospitalized, and one died. Seven cases were among people who were immunocompromised, including two perinatally infected infants. Both mothers likely had subclinical infections.

One case was part of a national outbreak related to Frescolina Marte brand ricotta salata cheese imported from Italy, which resulted in 22 cases and four deaths from 14 states. The product was recalled after the outbreak was identified.

DOH has received 12 to 25 reports of listeriosis per year during recent years.