Apr 15, 2010 (CIDRAP News) E coli O157:H7 was the comparative bright spot today in a federal report that showed little change in the incidence of most foodborne illnesses in 2009.
The report from the Centers for Disease Control and Prevention (CDC) showed the incidence of E coli was down 25% compared with the 2006-08 period and was the lowest since 2004. But most other pathogens changed little last year, and Vibrio cases, usually linked to shellfish, continued an unexplained climb that put them 85% higher than the rate in the late 1990s.
The incidence of Salmonella, the most common foodborne bug, is down only 10% from the period 1996-98, the CDC reported. That was when the agency launched its Foodborne Diseases Active Surveillance Network, or FoodNet, which gathers data on confirmed foodborne illnesses in 10 states and parts of states, with a combined population of 46 million. Today's report presents the preliminary FoodNet findings for 2009.
FoodNet counted 17,468 illnesses in 2009, the CDC reported in the Apr 16 issue of Morbidity and Mortality Weekly Report. Salmonella led the list with 7,033 cases, for a rate of 15.19 per 100,000 people. Other case counts and their rates were Campylobacter, 6,033, 13.02; Shigella, 1,849, 3.99; Cryptosporidium, 1,325, 2.86; E coli O157:H7, 459, 0.99; toxin-producing E coli non-O157:H7, 264, 0.57; Vibrio, 160, 0.35; Listeria, 158, 0.34; Yersinia, 150, 0.32; and Cyclospora, 31, 0.07.
At a news briefing today, Chris Braden, MD, acting director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, said E coli O157:H7 cases declined in the early years of FoodNet surveillance but later plateaued. With the decline last year, E coli incidence met the "Healthy People 2010" goal of no more than 1 case per 100,000 people, the CDC said.
The incidence remained higher than the 2010 targets for three other pathogens included in the national goals: Campylobacter, Listeria, and Salmonella.
"The interventions begun in the late 1990s were successful in decreasing some of these foodborne diseases, but we haven't seen much recent progress," Braden said in a CDC news release. "To make additional strides against these diseases and ultimately better protect the American people from foodborne illness, CDC, our federal and state partners, and the food industry will need to try new strategies."
Braden said factors that probably helped reduce E coli infections in 2009 included efforts to keep the pathogen out of ground beef and leafy greens.
In particular, said David Goldman, MD, MPH, of the US Department of Agriculture's Food Safety and Inspection Service (FSIS), last summer the FSIS expanded its E coli testing to include all components of ground beef, including "bench trim." Also, he said, "Last summer we issued instructions to all our employees to make sure plants are using sound sanitary practices in processing beef carcasses."
FoodNet identified 64 cases of hemolytic uremic syndrome, a severe and sometimes fatal renal complication of E coli infections, in children (those under 18) last year. Forty-two cases were in children younger than 5 years, which signaled an incidence of 1.40 per 100,000 for that age-group and was above the national target of 0.90, the CDC reported.
Another illness that dropped significantly last year was Shigella, down 27% from the 2006-08 period, the CDC said. But Braden said Shigella often spreads from person to person rather than via food. "The decrease in Shigella infections is more likely due to year-to-year fluctuations than specific prevention efforts," he commented.
The CDC reported that Salmonella infections declined slightly in 2009 but remained only 10% lower than in the 1996-98 period. Of the four foodborne illnesses for which there are national goals, Salmonella is furthest from the goal (15.19 per 100,000 versus 6.8 per 100,000), the agency said.
A possible reason for the slow progress in reducing Salmonella is that it spreads via a wide variety of foods and also by other routes, such as contact with baby chicks, pet turtles, other reptiles, and frogs, the CDC said in its news release.
The leading Salmonella serotype identified in 2009 was Enteritidis, which accounted for 19.2% of cases. At the press conference, Jeff Farrar, DVM, MPH, the Food and Drug Administration's (FDA's) associate commissioner for food protection, noted that the FDA's new rule for preventing Salmonella in shell eggs will take effect this summer. "Our estimate is that this rule may reduce Salmonella Enteritidis infections caused by eggs by up to 60%," he said.
Farrar also said the FDA is working on safety regulations for produce. "Produce safety is one of the most challenging issues we face," he said, adding that the agency has held many meetings to listen to stakeholders.
Concerning the increase in Vibrio cases, Braden observed that they constitute a small fraction of all foodborne illnesses, but some of the infections can be severe or fatal.
More than half of the Vibrio cases in 2009 involved V parahaemolyticus, which, said Donald Kraemer, deputy director of the FDA's Office of Food Safety, typically causes mild gastroenteritis. The CDC report said 14.3% of cases involved V vulnificus, which causes more serious disease.
Officials were at a loss to explain the increase in Vibrio infections. In response to questions, Kraemer said there has been no significant increase in shellfish consumption, and it's unclear whether climate change could be a factor.
He said V parahaemolyticus cases are typically attributed to exposure of shellfish to inappropriate temperatures after harvest. "What we've been trying to do is improve the practices of industry in that regard. States in the last couple of years have implemented some controls. But unfortunately we haven't seen the numbers come down. So what we're doing is taking a look at why that is."
He also noted that the FDA has proposed treatment methods to eliminate V vulnificus in oysters while keeping them raw, but acknowledged that that idea has run into industry opposition. "We're looking at costs associated with that and steps that would need to be taken for industry to move toward that," he commented.
The CDC report says that, for most infections, the incidence was highest in children under the age of 4, but people aged 50 and older were the most likely to be hospitalized and to die. Overall hospitalization rates ranged from 12.9% for Cyclospora infections to 89.2% for Listeria infections, while case-fatality rates ranged from 0.05% for Shigella cases to 12.7% for Listeria infections.
FoodNet surveillance does not include the identification of the specific food sources of contamination. Braden noted that in individual cases it's very difficult to determine which food made a person sick, since it could be anything he or she ate within 7 to 10 days before going to a doctor.
CDC. Preliminary FoodNet data on the incidence of infection with pathogens transmitted commonly through food10 states, 2009. MMWR 2010 Apr 16;59(14):418-22 [Full text]
Apr 15 CDC press release