By: James Peacock

Health officials announced on December 30, 2016, that they were releasing information about an outbreak of Salmonella Oslo that took place in April of 2016. This Salmonella outbreak sickened 14 people in eight states, but was not announced publicly until the December update. States affected by this outbreak include Nebraska with one case, Minnesota with two cases, Wisconsin with one case, Illinois with two cases, Michigan with three cases, Ohio with 2 cases, Kentucky with one case, and Massachusetts with two cases. These 14 illnesses took place between March 21, 2016 and April 9, 2016. This outbreak hit its peak rate of growth in late March, when more than half of the reported illnesses took place over a five-day span. People sickened in this outbreak ranged in age from 3 to 68 years. There were three people who required hospitalization because of their illness, and there were no deaths reported.

The process of investigating an outbreak occurs typically after there is a spike in illnesses. Because health officials have studied for years the average rate that specific pathogens cause illness, they are able to track when these background infections suddenly change. When a spike in foodborne illness rates are detected, health officials can then investigate the outbreak, usually by taking samples and by conducting interviews. These interviews, and the answers given by ill individuals, often lead to health officials finding the source of an outbreak. 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. While there are several types of testing, the most common pathogen testing reveals the bacteria’s DNA fingerprint. This fingerprint, a solution of the process of pulsed field gel electrophoresis (PFGE), is unique to the bacteria and strain involved in the outbreak. Other testing, including Whole Genome Sequencing, can help investigators better determine the genetic makeup of a pathogen. The DNA fingerprint, as well as any other genetic information,  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.

Health officials used the standard methods of investigation in this outbreak. The FDA, CDC, the Canadian Food Inspection Agency, and officials from several state departments of health all contributed to this outbreak investigation. Interviews were conducted with 13 out of the 14 total patients in this outbreak. Twelve out of the 13 people interviewed reported eating cucumbers prior to their illness. Eleven of these responses specifically referred to Persian cucumbers. No other produce products were reported as commonly as mini cucumbers. This led investigators to conclude that Persian cucumbers were the source of the outbreak, making this the fourth Salmonella outbreak linked to cucumbers since 2013. Out of the people who reported consuming mini cucumber prior to their illness, eight people reported buying mini cucumbers from the same store chain. This store, though it was not named, promptly removed all mini cucumbers from their shelves. Health officials cite a quick response as one of the reasons that this outbreak did not get much worse. Though Persian cucumbers were said to be the source of the outbreak, the supplier of these cucumbers was never located. Health officials have said that these cucumbers could have come from Canada, Mexico, and the Dominican Republic. Although cucumbers were more than likely distributed to Canadian provinces, no illnesses matching the US cases were reported. There were also no Salmonella bacteria found in samples taken from cucumbers. What made this outbreak so unique was what happened after the genetic testing was done. It was soon revealed that the strain of Salmonella Oslo, which is one of the rarest types of Salmonella, responsible for this outbreak was not found in the PulseNet system. There had been no infections or outbreaks caused by genetically similar types of Salmonella Oslo. This resulted in a series of genetic tests being done in order to ensure that a complete profile of this strain of Salmonella was added to the PulseNet system.

Salmonella infections are one of the most common forms of foodborne illness. Health Officials first tracked Salmonella in 1962, but they first detected Salmonella long before this time. Dr. Salmon first discovered the bacteria and its effects more than 125 years ago. There are many different strains of Salmonella bacteria, but all will cause illness in humans. The 32 different serotypes, or strains, of Salmonella bacteria help investigators pinpoint potential outbreaks, as well as their source. The Centers for Disease Control and Prevention estimates that Salmonella bacteria infects about 1.2 million people each year in the United States. This leads to the hospitalization of about 19,000 people each year. Every year there are an estimated 450 deaths caused by Salmonella infections. After being exposed to the bacteria, a Salmonella infection will usually produce symptoms between 12 and 72 hours. Usually, Salmonella infections will produce symptoms including vomiting, fever, abdominal cramping, and nausea. While a Salmonella infection may subside on its own within a week, the infection may worsen or cause severe dehydration. This may make hospitalization necessary. Those with certain risk factors, including the elderly, children, and those with suppressed immune systems may be at an increased risk of developing a serious Salmonella infection. Early diagnosis of a Salmonella infection, as well as obtaining treatment, could greatly reduce the likelihood of future problems. It is important to keep in mind that meats should be cooked to an internal temperature of 160 degrees Fahrenheit in order to eliminate any foodborne pathogens. Fruits and vegetables should also be thoroughly washed or cooked. Salmonella bacteria can be found in a variety of different products, so it is important to always be cautious. If you or a loved one begin to show the symptoms of Salmonella poisoning, contact a medical professional.

 

Sources:

https://www.cdc.gov/mmwr/volumes/65/wr/mm655051a3.htm?s_cid=mm655051a3_x

https://www.cdc.gov/salmonella/index.html