By: James Peacock

The CDC has announced that in the middle of 2016, there was a Salmonella outbreak linked to hot peppers. In June, the CDC program PulseNet detected a cluster of 16 cases of Salmonella poisoning. All of these cases of illness have nearly identical pulsed-field gel electrophoresis (PFGE) patterns. PFGE is a test that shreds the DNA of a bacterial sample and then runs it through an electrified gel solution. The results of this test reveal a ladder-like arrangement of DNA strands. These strands, when taken together, make up a bacteria’s DNA fingerprint. This fingerprint is unique to that specific strain of bacteria, making it easy to detect a pattern in tested samples. The DNA fingerprints are uploaded to the PulseNet system, where they are monitored in case multiple fingerprints begin to show up. In this case, 16 nearly identical fingerprints of Salmonella Anatum were uploaded in a relatively short time span. Salmonella Anatum is a fairly rare strain of Salmonella. Though it is among the 20 most common strains of Salmonella to cause illness, cases of Salmonella Anatum infections only make up 300 to 350 of the estimated million cases of Salmonella poisoning each year. Salmonella Anatum also made an appearance in the PulseNet system when a sample was taken from an Anaheim pepper also had the same DNA fingerprint. Thirty-two people would eventually be sickened in the outbreak in nine different states. Texas and Minnesota were the hardest hit in the outbreak, but illnesses were also reported in Louisiana, Georgia, Oklahoma, Kansas, Illinois, Ohio, and Pennsylvania. Even though the investigation would indicate that hot peppers were the cause of the outbreak, neither a specific pepper nor a specific supplier was successfully identified.

In addition to sample testing, including PFGE tests and whole genome sequencing (WGS), the process of investigating an outbreak usually also includes the conducting of interviews. There is sometimes a correlation between interview answers, which can help investigators locate a source. Over the course of this outbreak investigation, the CDC was able to conduct interviews with 14 out of the 32 people affected by the outbreak. As a part of these interviews, investigators asked about recent food items that ill persons had consumed. The most commonly named food was tomatoes, where seventy-one percent of respondents reported eating them prior to becoming ill. Also reported by interviewees was pork with 64% of respondents, avocado/guacamole with 57%, jalapenos with 36%, and cantaloupe with 36%. These responses were then compared to average data collected by the CDC in the 2006-2007 FoodNet Population Survey. The only food that was reported at a greater rate than the reported average was avocados/guacamole. The FoodNet Population Survey, however, does not include questions about jalapenos.

Traceback Investigation

Out of the thirty-two cases reported, the median age of those affected was 36 years, and the illnesses were reported between May 6 and July 9, 2016. Eight people were hospitalized among the 25 patients for whom information about hospitalization was available. There were no deaths reported in this outbreak. Fourteen people reported eating hot peppers. This, plus the Salmonella positive sample taken from Anaheim peppers, led investigators to attempt to trace the source of the outbreak back to a supplier of hot peppers. Even though no Anaheim peppers were reported to be eaten by patients, investigators believe that this may be because Anaheim peppers are harder to identify because they are less common. A traceback investigation is conducted by health investigators in an effort to connect an ill person with the supplier or source of the contaminated food. This is usually done by tracing the potentially contaminated food as far back as necessary until the source of the contamination is established. The investigation looked at three different restaurants in Minnesota and Texas where patients reported eating prior to becoming sick. Two out of these three restaurants reported using the same consolidator in Mexico. The third restaurant had also previously used the same consolidator prior to the outbreak but had since switched. A consolidator gathers foods from several different farms or growers. This can make it difficult to track down a specific farm that contaminated foods came from. The consolidator in question was dubbed consolidator B by investigators. The Salmonella-positive sample taken from an Anaheim pepper was sold by consolidator B. The FDA then collected seven other hot pepper samples, from peppers including serrano, habanero, jalapeno, and bell peppers. The FDA placed consolidator B on import alert on June 21, 2016. An import alert holds any product from being imported into the United States until it is proven that there is no contamination present. After the import alert was put in place, only two extra illnesses occurred. With all of this evidence, investigators were able to point towards hot peppers as a likely source of the outbreak. When it came to finding a consolidator or farm where the contamination took place, though, there was much more difficulty. As the chart below shows, there is a large web of different distributors and consolidators, which made it nearly impossible to pin down an exact source.

What is Salmonella?

Salmonella bacteria are one of the most common causes of gastrointestinal illness in America. The CDC estimates that Salmonella causes about 1.2 million cases of illness per year. Salmonella is also a very common cause of foodborne illness outbreaks. Foods including meats, poultry, dairy, fish, peanut butter, and produce have been connected to outbreaks. A study done in 2009 found that Salmonella bacteria grow more easily in jalapenos than in other raw vegetables. A case of Salmonella poisoning usually produces symptoms between 12 and 72 hours after infection. Symptoms of Salmonella poisoning typically include vomiting, abdominal cramping, fever, and nausea. Generally, an infection will go away on its own within a week, although Salmonella infections may worsen. Those with certain risk factors, including children, the elderly, and those with suppressed immune systems may be at an increased risk of developing a serious case of Salmonella poisoning. If you or a loved one begins to show the symptoms of Salmonella poisoning, contact a medical professional.

 

Sources:

https://www.cdc.gov/mmwr/volumes/66/wr/mm6625a2.htm?s_cid=mm6625a2_w