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MMWR & The Burden of Food Poisoning

Posted in Food Safety on October 18, 2018

United States has been taking continuous food safety measures, but the burden of food poisoning still has taken a toll on the government. So, CDC examined the trends of foodborne illnesses in 2017 and also detailed on the changes in its incidence since 2006 in their Morbidity and Mortality Weekly Report (MMWR) for March 23, 2018. In 2017, FoodNet reported a total of 24,484 infections, 5677 hospitalizations, and 122 deaths.

The Breakdown

When you compare the numbers with the 2014 – 2016 statistics, the incidence of infections for Campylobacter, Listeria, STEC E.Coli, Vibrio, Cyclospora, and Yersinia have increased. The increase, however, is also attributed to the fact that the testing was previously limited, and the rates of reporting of illnesses have grown. This is likely due to escalated use and sensitivity of the culture independent diagnostic tests. In 2017, infections related to Salmonella serotypes Typhimurium and Heidelberg decreased as compared to 2006-2008 and the incidence of serotypes Infantis, Thompson and Javiana increased. The decrease could be because of the new regulatory techniques that mandate testing of Salmonella in various poultry products. Cases of STEC E. coli O157 also have decreased in 2017, along with reductions of these isolations from beef when the numbers are compared to 2006-2008.

FoodNet – The Driving Force

FoodNet is a collaboration between CDC, USDA-FSIS, 10 state health departments, and the FDA. They conduct population-based surveillance for infections caused by Campylobacter, Listeria, Vibrio, Shigella, STEC, Cyclospora, Cryptosporidium, Salmonella, and Yersinia in 10 sites that have 15% of the US population (around 46 million people). Laboratory diagnosed bacterial infections is basically defined as isolation of the bacteria from a specimen with the help of culture or identifying using CIDT. CIDTs help in detecting nucleic acid sequences and bacterial antigens.

Incidence per 100,000 population is estimated by dividing the number of infections in 2017 by the surveillance area population in 2016. Since there have been so many changes in testing practices since 2006, incidence comparisons to 2006-2008 uses only culture confirmed bacterial infection but the incidence comparisons with 2014-2016 uses both culture confirmed and CIDT positive cases.

Infections Cases, Incidence and Trends

In 2017, incidence of infections per 100,000 population were as follows

  • Campylobacter – 19.2
  • Salmonella – 16.0
  • Shigella – 4.3
  • STEC – 4.2
  • Cryptosporidium – 3.7
  • Yersinia- 1
  • Vibrio – 0.7
  • Listeria – 0.3
  • Cyclospora – 0.3

Percentages of all those infections that were CIDT positive-only included those that had culture negative and were not tested for the culture includes Yersinia (51%), Campylobacter (36%), Shigella (31%), Vibrio (29%), Salmonella (9%) and Listeria (1%). The incidence of 2017 was significantly higher as compared to 2014-2016 with a 489% increase for Cyclospora, 166% increase in Yersinia, 54% increase in Vibrio, 28% increase in STEC, 26% increase in Listeria and a 10% increase in Campylobacter. There was an overall 96% increase in the bacterial infections diagnosed by CIDT in 2017 as compared to the numbers during 2014-2016. The percentage of positive cultures among the specimens on which reflex culture was done, the numbers were around 38% for Vibrio to 90% for Salmonella.

Incidence of Salmonella and its serotypes:

The 5 most common serotypes of Salmonella among the 6373 (89%) of the fully serotypes isolates were

  • Enteritidis – incidence of 2.6 per 100,000
  • Typhimurium – incidence of 1.4 per 100,000
  • Newport – incidence of 1.3 per 100,000
  • Javiana – incidence of 1.2 per 100,000
  • Monophasic variant of Typhimurium

Among the 13 of the most common serotypes, the incidence for Heidelberg in 2017 was 65% lower when compared to 2006-2008 and 38% lower when compared to 2014-2016. For Typhimurium, the numbers were notably lower with 42% and 14% respectively.

STEC E. coli Trends:

A total of 1473 STEC isolates were tested for the O157 antigen and out of them, a total of 413 (28%) cases were determined to be O157. Among the 766 non-O157 STEC isolates whose serogroup were determined, the most common were O26 with 29% cases, O103 with 26% of cases and O111 with 18% of cases. The incidence of the non-O157 STEC notably increased by 25% during 2017 as compared to that of 2014-2016 and the incidence of STEC O157 remains unchanged. However, when you compare the numbers for STEC O157 with 2006-2008, the numbers were significantly lower and there was a 35% decrease in the incidences.

HUS Trends:

FoodNet determined a total of 57 cases of HUS among children with an incidence rate of 0.51 per 100,000 during 2016 and 35 (61%) occurred among the children aged less than 5 years, so the incidence is 1.18 per 100,000. When you compare the incidence of 2016 with that during 2013-2015, then the numbers are not significantly different among all the children or those that are aged less than 5 years. The incidence, however, notably decreased by 36% in children aged less than 5 years during 2016 as compared to the time period 2006-2008.


There has been a rapid increase in the culture independent diagnostic testing. In the previous years, stool test only consisted of the methods that included finding Salmonella, Shigella, Campylobacter and STEC O157. These panel tests more than often included Yersinia, Vibrio, Cyclospora and non O157 STEC, which most likely were the reason for their increase in 2017.

CIDTs are not able to subtype the pathogens, detect outbreaks when the reflex culture is performed or find antimicrobial susceptibility. Because of these reasons, the Association of Public Health Laboratories has recommended that the clinical labs do culture CIDT positive specimens. CIDTs are able to come up with the results more quickly which has increased incidence of the infection. Infection that remain undetected with the culture methods might be found with better sensitivity and specificity of the DNA based CIDTs.

The report concludes by stating that most of the outbreaks and illnesses can be prevented. It states:

“Most foodborne illnesses can be prevented. New regulatory requirements aimed at reducing contamination of poultry meat might have contributed to decreases in incidence of infections caused by Salmonella serotypes Typhimurium and Heidelberg. Vaccination might also have contributed, but the extent of vaccination in poultry broiler flocks has not been reported. The declines in these and in STEC O157 infections provide supportive evidence that targeted control measures are effective. More control measures are needed and might be achieved with continued implementation of the FDA Food Safety Modernization Act,§§ new or revised meat and poultry performance standards, and enhanced training and guidance for industry and inspection personnel. In particular, measures targeting specific Salmonella serotypes, including vaccination of broiler poultry flocks, might result in a marked decrease in human illness, as has been seen in the United Kingdom.”

We can surely see a difference with continued implementation of the FDA Food Safety Modernization Act, more control measures, revised poultry, seafood and meat performance standards etc.

By: Pooja Sharma, Contributing Writer (Non-Lawyer)