Salmonellosis unchanged, other illnesses decline

Published on August 15, 2011
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The incidence of Salmonella-related illness has been nearly level since the mid-1990s, despite a one-fifth decrease in the overall rate of foodborne illness in the preceding decade, according to a report from the Centers for Disease Control and Prevention.
Federal public health officials had hoped to reduce rates of illness associated with salmonellae and three other foodborne pathogens by half over a 10-year period. But that goal was met for only one: shiga toxin-producing Escherichia coli O157:H7. Rates of illness associated with the other two pathogens, Campylobacter and Listeria, were reduced about 45 percent and 36 percent, respectively.
The CDC released in early June a report on the 2010 FoodNet surveillance, a program that covers 15 percent of the U.S. population and involves collaboration from the CDC, the Department of Agriculture, and the Food and Drug Administration. Recorded Salmonella cases affected about 17.6 of every 100,000 people in the surveillance area during 2010, up from about 14.5 per 100,000 people in 1996, when FoodNet completed its first year of surveillance
Illnesses recorded per 100,000 people in FoodNet surveillance:
Source 1996 2010 2010
Healthy People goal
Healthy People goal
Campylobacter 23.6 13.6 12.3 8.5
Listeria 0.46 0.3 0.24 0.2
Salmonella 14.5 17.6 6.8 11.4
STEC O157 2.6 0.9 1 0.6
STEC non-O157 -- 1 N/A N/A
Shigella 8.9 3.8 N/A N/A
Vibrio 0.15 0.4 N/A 0.2
Yersinia 1 0.3 N/A 0.3

FoodNet information provided by the CDC through reports on illness rates and the June 10
Morbidity and Mortality Weekly Report.

"There are a lot of challenges with Salmonella because it is so widespread in nature, there are numerous serotypes and animal reservoirs, and this is a bacteria that has proven to be very hardy and can persist in the environment under very harsh conditions for weeks or months," said Dr. Kristy K. Bradley, president of the National Association of State Public Health Veterinarians and Oklahoma's state public health veterinarian.

Olga L. Henao, PhD, lead author of the CDC report and the team lead for FoodNet, said that the multiple sources of Salmonella infection—including meat, produce, reptiles, and amphibians—don't allow for those working to reduce illnesses to target particular sources of infection. She also noted that the varied serotypes of Salmonella have varied behaviors, and that examining patterns of illness related to those serotypes could lead to changes in activities and further reduce the incidence of foodborne illnesses.

On the basis of surveillance data from 1996-1998, the CDC report indicates the incidence of illness from Salmonella enterica serotype Typhimurium decreased by 53 percent by the time of the 2010 surveillance. Illness from Salmonella enteritidis increased 76 percent in that time and illness from Salmonella Newport increased 116 percent, making them the first and second most common causes of salmonellosis.

"Each of those serotypes behaves a little bit differently, and so for some of the serotypes we're seeing increases, such as Salmonella enteritidis," Dr. Henao said. "For others, we're seeing consistent decreases, such as with Salmonella Typhimurium."

Dr. Henao said examining patterns of illness by serotype will lead to examination of activities that could be targeted to further reduce illnesses by those pathogens. For example, she noted that S enteritidis has historically been associated with eggs and poultry, and actions to reduce infections with such bacteria could involve controlling contamination of those foods.

Since July 2010, egg producers with more than 50,000 hens have been required to take additional precautions regarding purchases of birds, sanitation, testing, and egg storage. The FDA rules, which are intended to reduce the number of illnesses caused by S enteritidis, will also affect any producer with more than 3,000 hens starting in July 2012. FDA officials have estimated the rules will reduce infections with the bacteria by 60 percent.

Dr. Bradley said veterinarians can help reduce illnesses through education of livestock-owning clients on good husbandry practices and through preventive care. Veterinarians working in processing and slaughter facilities also impact safety through enforcement of regulations and policies that safeguard against contamination.

Dr. Bradley also said veterinarians in companion animal medicine can help prevent illnesses among their clients. She noted that recent illness clusters and outbreaks have involved Salmonella in pet food and treats, as well as contact with pets such as frogs, Easter chicks, and reptiles. She encourages documenting the brands and types of foods eaten by pets with enteric illnesses.

Health program sets new goals

The Department of Health and Human Services, through its Healthy People 2010 program, had set a goal of reducing by half the rate of illnesses from Salmonella from a 1997 baseline of 13.6 per 100,000 people. The department's new goal under the Healthy People 2020 program calls for reducing incidence by a quarter, from the 2009 rate of 15.2 per 100,000 to a 2020 rate of 11.4. 

Dr. Henao said the Healthy People 2020 goals were based on factors such as achievements over the preceding decade and the believed feasibility of reducing illnesses. Regulations, changes in food processing, and changes in consumer behavior all could lead to decreases in illness such as those related to E coli O157:H7.

While Listeria infections were far less common and connected with fewer deaths than Salmonella infections, they were the most dangerous. About 90 percent of people confirmed to have listeriosis in 2010 were hospitalized and 13 percent died.

The Healthy People 2020 program calls for reductions of a third for Campylobacter, half for STEC O157:H7, and a quarter for Listeria.

Dr. Henao said that, in addition to federal efforts to reduce foodborne illness, local and state health departments are important for further reducing harm because of their roles in receiving illness reports, conducting investigations, and identifying factors related to illnesses. She added that knowledge of human illness is insufficient without knowledge of people's interactions with pathogens and environments, and she said it is important for scientific disciplines to work together to understand all factors associated with illness.