By: Candess Zona-Mendola

On July 15 2016, the CDC announced that they were concluding the investigation into the Listeria outbreak associated with frozen vegetables produced by CRF Frozen Foods. A total of nine people have been sickened by Listeria monocytogenes since the outbreak’s initial announcement in early May. In this final update, there was only one more case of illness reported. The nine cases of illness took place over four years, with the earliest Listeria infection taking place in September 2013. Five more infections occurred in 2015, and the last three infections took place in early 2016. All nine people infected in the outbreak needed to be hospitalized because of their illnesses. There were three deaths reported, one in Maryland, Connecticut, and Washington. In one of the deaths, Listeriosis was considered to be the cause of death, while the other two deaths were not caused by Listeriosis. The nine cases of Listeria poisoning linked to the outbreak were spread across four states. States affected include California with six cases, Connecticut with one case, Maryland with one case, and Washington with one case. The CDC was first notified of the outbreak in March of 2016, when they received reports of two cases of illness. One more case of illness would be reported to them over the course of the investigation, bringing the total to three cases in 2016. The CDC was able to link the other six cases of illness to the outbreak through the PulseNet database.

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The PulseNet database is a collection of DNA fingerprints collected throughout outbreak and recall investigations. Public health investigators take samples of bacteria from ill people or contaminated products and use a technique called pulsed-field gel electrophoresis (PFGE) to determine that bacteria’s DNA fingerprint. This fingerprint, made up of DNA that was shredded and processed by PFGE, is specific to the strain of bacteria in the sample. Health investigators then send their data to the CDC, who adds it to the database. When multiple samples have matching DNA fingerprints, it could be a sign that an outbreak has occurred. The PulseNet system was first implemented in 1996, and the CDC reports that the database helps identify about 30 outbreaks per year.

Although the outbreak is considered over, there may still be contaminated products in the homes of consumers. The CDC warns that consumers could still become sick. This Listeria outbreak was accompanied by a myriad of recalls. Over 450 products were eventually recalled because of the contaminated frozen vegetables. The original recall was announced on April 23, 2016, when CRF Frozen Foods recalled 15 items that had the potential to be contaminated by Listeria monocytogenes bacteria. The Pasco, Washington company had previously been notified by state health officials that Listeria bacteria had been found over the course of routine testing. CRF Frozen Foods halted production at its Pasco, Washington facility on April 22, 2016. The original recall only covered merchandise produced between September 23, 2015, and March 16, 2016.

The recall was expanded on May 2, 2016, just one day before the CDC investigation announcement. The new recall included all products that CRF had produced in its Pasco, Washington facility between May 1, 2014 and May 2, 2016. This expansion added more than 300 products to the recall, bringing the total to 358. Forty-two different brands were affected by the recall. The recall also expanded the types of products recalled. The original recall was limited to peas, corn, and edamame. The expansion added broccoli, butternut squash, cauliflower, green beans, kale, Italian beans, leeks, lima beans, pepper strips, onions, potatoes, sweet potatoes, spinach, blueberries, cranberries, cherries, raspberries, and strawberries to the list of products potentially contaminated with Listeria bacteria. The recall expansion, because it involved so many brands, led to multiple secondary recalls. All of these products were either processed by CRF Frozen Foods or used contaminated frozen vegetables as an ingredient. The recall, and its secondary recalls, affected products that were distributed across all 50 states in the United States and to 5 provinces in Canada. Notable secondary recalls came from Kroger, Trader Joe’s, and Costco.

In March 2016, the FDA found Listeria in environmental samples taken from the Oregon Potato Company, which is located in Pasco, Washington. These Listeria bacteria, through the use of the PulseNet system, were found to be closely genetically related to eight different samples taken from people sickened in the outbreak. Based on this, Oregon Potato Company issued a voluntary recall of wholesale onion products. This recall lead to another bunch of secondary recalls. The FDA reports that at least 456 products were affected by the recall. Three hundred and fifty-eight of the products were recalled by CRF Frozen Foods, and 98 other products were recalled by firms that were distributed products from CRF Frozen Foods. A list of all 456 recalled products can be found here.

Again, the CDC warns that just because the investigation is over does not mean that the risk of infection is no longer there. Because these products are frozen, they have a much longer shelf life, and may still be in the freezers of consumers who have not heard about the recalls and outbreak. Listeria bacteria is incredibly durable, and can even thrive in freezing temperatures. Because of this, there is still a risk of infection if any recalled products are consumed. The CDC recommends that any consumers or restaurants that find recalled products in their freezer throw them away immediately to prevent infection. Listeria infections can be very serious, and can be life threatening in young children, the elderly, and those with suppressed immune systems. Pregnant women are also at an increased risk of a serious Listeria infection, which can cause miscarriage, serious illness, stillbirth, and premature labor.

Although it is very serious, Listeria is a fairly rare form of foodborne illness. The CDC reports that only about 1600 cases of Listeria infection occur each year, but the severity of these infections has led the CDC to declare it an important health problem in the United States. Listeria bacteria cause a disease called Listeriosis, which can occur between 3 and 70 days after ingesting Listeria bacteria. The large range in the incubation period is due to Listeria’s ability to remain dormant in the body for up to two months before causing an infection. Once the infection appears, it will cause symptoms including muscle aches, headaches, diarrhea, nausea, fever, and stiff neck. If you or a loved one begins to show the symptoms of a Listeria infection, contact a medical professional.