By: James Peacock

The CDC published their final update to an outbreak that had been under investigation since mid March on December 14. In this update, they stated that the number of cases of Listeria poisoning would remain at 2. These two cases of illness actually date back to 2014, but the CDC was unaware of their connection to a foodborne illness outbreak until January 29, 2016. After their initial announcement on March 17, the investigation was left open due to the chance that other illnesses may surface. When months passed with no updates to the outbreak, the CDC decided to end its investigation. The two people who were sickened were in different states, California and Florida. Both of these people required hospitalization for their illnesses. There was one death reported in Florida, and Listeriosis is considered to be a contributing factor. The investigation into the illnesses revealed that the likely source of the outbreak was Miller’s Organic Farm. This connection to the outbreak was discovered after health officials took samples from a batch of raw chocolate milk produced by the Organic Farm. When the sample tested positive for Listeria monocytogenes bacteria, officials ran further tests, and were able to determine that the samples taken from the raw milk were genetically similar to the samples taken from ill individuals.

The process of investigating an outbreak usually occurs after there is a spike in illnesses. Health officials have studied for years the average rate that specific pathogens cause illness, and are able to track when these background infections suddenly change. When a random spike in illnesses is detected, health officials can then investigate the outbreak, usually by taking samples and by conducting interviews. There is sometimes a correlation between interview answers, which can help investigators locate a source. Although interviews can help locate potential sources, the best way for health officials to learn more about an outbreak is through the testing of samples. When medical providers retrieve samples from ill people or from the environment, the samples undergo testing to learn more about them. This type of testing reveals is the bacteria’s DNA fingerprint. This fingerprint, a solution of the process of pulsed field gel electrophoresis, is unique to the bacteria and strain involved in the outbreak. The DNA fingerprint is then uploaded to the PulseNet system. The PulseNet system is a database of DNA fingerprints maintained by the CDC. If a saved sample matches another sample, there may be a connection between the two. When multiple samples match through the PulseNet system, it is another clue to investigators about the origin and size of the outbreak. In the case of this outbreak, the PulseNet system was the only reason this outbreak received an investigation. Because the illnesses actually took place in 2014, it was not until the PulseNet system marked the two samples as genetically related that the outbreak was detected.

Raw milk continues to be a pressing issue in the United States. With multiple outbreaks of foodborne illnesses occurring each year at the hands of unpasteurized milk, the CDC and other health officials have to constantly remind people not to drink raw milk or consume products made with raw milk. It is only through the process of pasteurization that milk can have all of its potential pathogens destroyed. This process was developed by Louis Pasteur in the 1800s and represented one of the first forays into understanding how illnesses spread. The process involves heating milk, or other liquids, to the point that all potential pathogens can no longer exist in that environment. Unpasteurized milk has the propensity to contain bacteria, including E. coli, Salmonella, and Campylobacter, among others.

Listeria monocytogenes bacteria first became known as a foodborne illness in 1981. Although it had received previous study, it was not until a major outbreak in Canada that the pathogen began to gain more attention. The CDC began to track LIsteria infection more than 30 years ago. In the 1990s, most outbreaks were caused by deli meats and hot dogs. Since then, though, there have been Listeria outbreaks caused by a wide variety of products, including unpasteurized juices and milk, the products made with these raw liquids, sprouts and other vegetables, and smoked seafood. Deli meats continue to be a leading cause of Listeria outbreaks. The CDC now estimates that there are about 1600 cases of illness caused each year by Listeria bacteria. This leads to about 260 deaths per year. There are several risk factors that make an individual more likely to develop a LIsteria infection. Newborns, older adults, and people with suppressed immune systems are all at an increased risk. Pregnant women are also about 10 times more likely to develop a Listeria infection.

Listeria monocytogenes bacteria are an especially dangerous form of foodborne pathogen. They have the ability to survive, and even thrive, in very cold environments. This means that freezing the bacteria will not kill them, nor will it hamer their growth. This was seen in the Blue Bell outbreak in 2015, in which 10 people were sickened with Listeria poisoning after consuming frozen ice cream. Because Listeria bacteria has also been linked to m=numerous raw products, including sprouts and raw milk, the CDC recommends that the only way to properly remove LIsteria bacteria is to cook products thoroughly. This makes it especially important to cook meats to an internal temperature of 160 in order to prevent the survival of any contamination.

The testing process for a Listeria infection is a simple tissue sample used to foster the growth of a bacterial culture. If Listeria is seen in the culture, then the individual who provided the sample has tested positive for a Listeria infection. This infection is usually treated with antibiotics. The Listeria poisoning itself may not produce symptoms for up to two months after the infection, although symptoms usually present within 3-10 days. Listeria infections often produce similar symptoms to other foodborne illnesses, including fever and diarrhea. However, if the infection becomes invasive, meaning it has left the gut, the symptoms can worsen. In pregnant women with invasive Listeria, fever, fatigue, muscle aches, and diarrhea are all common symptoms. However, Listeria has been known to cause miscarriage, stillbirth, infection in newborns, or premature delivery. In individuals with invasive Listeria who are not pregnant, fever, diarrhea, headache, stiff neck, confusion, convulsions, loss of balance, and muscle aches are all common symptoms. If you or a loved one begin to show the symptoms of Listeria poisoning, contact a medical professional.