King County Public Health is reporting the third case of Listeria monocytogenes linked to the University of Washington Medical Center (UWMC). In December 2014, two patients drank milkshakes made from Snoqualmie ice cream that was recalled for Listeria monocytogenes contamination. On Wednesday, December 9, 2015, a third patient was sickened with the same strain of Listeria bacteria.
That patient drank a milkshake made in the same machine that produced the contaminated milkshakes last year. Samples of the ice cream that is now used to make milkshakes have tested negative for the pathogenic bacteria, but the facility’s ice cream machine tested positive for Listeria monocytogenes bacteria. The machine uses a commercial liquid ice cream product to make soft serve ice cream and milkshakes.
All three patients had “highly weakened immune systems” according to the report. UWMC has stopped using the machine. All three patients have recovered from their infections.
Dr. Jeff Duchin, Health Officer for Public Health – Seattle & King County answered questions about this outbreak. The genetic fingerprints of the bacteria taken from the three patients match, as confirmed by pulsed field-gel electrophoresis. They match the bacteria found in the ice cream machine, and the bacteria found in Snoqualmie ice cream.
Listeria monocytogenes bacteria is notoriously difficult to erase from machines and food preparation areas. Dr. Duchin said, “Listeria can survive for long periods despite efforts to clean and sanitize food-processing equipment. UWMC cleaned and sanitized their machines twice weekly, which is not as frequently as is recommended.” Listeria bacteria can grow at refrigerator temperatures, easily survives freezing, and can become aerosolized, contaminating other surfaces and machines.
Listeria can only be killed by heat or bleach and is a remarkably persistent and hardy bacterium. If fat remains in processing equipment, biofilms can develop. These films provide nutrients for the attachment and growth of Listeria monocytogenes bacteria. The bacteria can hide in rollers, motor housings, ice makers, air filters, and lines and hoses.
UWMC stopped using the machine on November 25, 2015. But listeriosis, the illness caused by this bacteria, can take up to 70 days to appear. most patients become ill within a few weeks. Anyone who was a patient at UWMC, especially those with weakened or compromised immune systems, pregnant women, or anyone who ate soft ice cream or a milkshake at UWMC should monitor themselves for the symptoms of this illness.
The symptoms of listeriosis include fever, muscle aches, stiff neck, diarrhea, upset stomach, loss of balance, and confusion. Pregnant women may only be mildly ill with symptoms similar to the flu, but listeriosis can cause miscarriage, stillbirth, and a serious or deadly infection in the newborn baby. Some doctors treat pregnant women with prophylactic antibiotics if they consumed food that may be contaminated with deadly Listeria monocytogenes bacteria.
