Listeria Outbreak With Unknown Source Turns Deadly

A Listeria monocytogenes outbreak has turned deadly in Michigan and health officials have yet to identify the direct source of the outbreak.

On April 17, 2019, the US Centers for Disease Control and Prevention (CDC) released an outbreak investigation notice for 8 cases of Listeria occurring between November 13, 2016, and March 4, 2019. Isolates collected from the ill individuals were processed via whole genome sequencing, which found close genetic relation of the strains, indicating it is likely that the ill share a common source of infection.

The ill individuals hail from 8 states and range in age from 40 to 88 years, with a median age of 57. All 8 individuals were hospitalized.

As part of the investigation, health officials asked affected individuals about their consumptions and exposures in the 4 weeks prior to falling ill. In total, 6 individuals were interviewed, 5 of whom reported eating products sliced at a deli counter such as meats or cheeses.

Health investigators with the US Department of Agriculture’s Food Safety and Inspection Service and the US Food and Drug Administration performed traceback investigations at delis where the hospitalized individuals reported purchasing products. The delis served a variety of brands and limited information was available; therefore, the investigators could not identify if a common meat or cheese product is responsible for the outbreak.

The CDC’s statement reports that the outbreak strain was identified in samples collected from meat products from a deli and deli counters in multiple retail locations in New York and Rhode Island. Whole genome sequencing indicates that the strain from the samples is closely related to the strain collected from the ill individuals. Although this provides more evidence that the outbreak is linked to deli-sliced products, a common source has yet to be identified.

At this time, there is no recommendation for the avoidance of any specific products sold at delis. The CDC does, however, indicate that pregnant women and their babies, adults over the age of 65, and individuals with weakened immune systems should handle deli products carefully, as these populations are at a higher risk for severe Listeria infection.

Symptoms of Listeria include fever, muscle aches, headache, stiff neck, confusion, loss of balance, and convulsions. Symptoms of invasive Listeria infections usually present 1 to 4 weeks following exposure and can be treated with antibiotics.

Listeria bacteria can persist at low temperatures and be easily spread to other products and surfaces, therefore individuals who handle these products should wash their hands and regularly clean contact surfaces, equipment, and utensils.

The CDC will provide updates as more information becomes available.

For a list of states affected by the Listeria monocytogenes outbreak with a suspected link to deli products, consult the Contagion® Outbreak Monitor.