CDC says some foodborne illnesses rose in 2006

Apr 12, 2007 (CIDRAP News) – Preliminary data from 2006 show that foodborne illnesses caused by Escherichia coli and Vibrio rose, while cases caused by other pathogens leveled off or slowly declined, the Centers for Disease Control and Prevention (CDC) announced today.

The data come from the CDC's FoodNet surveillance system, which covers about 15% of the US population and collects information from 10 states. A report detailing the 2006 findings appears in the Apr 13 issue of Morbidity and Mortality Weekly Report.

Increases in E coli cases over the past 2 years have erased declines that occurred in 2003 and 2004 when beef-processing safety measures took effect, and the number of Vibrio infections rose to its highest level since FoodNet surveillance began in 1996.

CDC director Julie Gerberding, who introduced the report today at a press conference, said the results show that more work needs to be done on the food safety front, particularly in the fresh-produce industry, which in 2006 had nationwide outbreaks involving spinach, tomatoes, and lettuce. "We need ongoing work to reduce exposure of our produce to E coli O157," she said.

Robert Tauxe, deputy director of the CDC's division of foodborne, bacterial, and mycotic diseases, told reporters that to reduce fresh produce–related illnesses, the industry should follow the example of the meat industry, which saw outbreaks decrease after it developed a set of food safety engineering principles.

"The meat industry shared information among themselves, in a noncompetitive arena, about what was successful," he said.

The CDC uses FoodNet data to assess national trends in foodborne illness. The agency compares each year's disease outbreak totals with data from 1996 through 1998, the first 3 years of FoodNet's surveillance program. The CDC noted that Campylobacter, Listeria, Shigella, and Yersina infections continued a slow decline from that baseline period, though most of the decrease occurred between 1999 and 2002.

FoodNet surveillance identified a total of 17,252 laboratory-confirmed foodborne infections in 2006. Salmonella accounted for 6,655 cases, about 39% of the total. There were 5,712 Campylobacter cases, about 33% of the total. The CDC reports 2,736 Shigella cases, 859 Cryptosporidium cases, and 590 cases of Shiga toxin–producing E coli (STEC) O157. The rest of the cases included STEC non-O157 (209), Yersinia (158), Vibrio (154), Listeria (138), and Cyclospora (41).

The FoodNet system recorded 71 cases of hemolytic uremic syndrome, a life-threatening complication of E coli O157 infections, among children in 2005, the latest data available, which is up from 44 cases in 2004.

Compared with the CDC's 2005 report, the new report shows little change in illness rates for many of the pathogens FoodNet tracks. The rate of salmonellosis cases in 2006 was 14.81 per 100,000 people, compared with 14.55 in 2005. The 2006 and 2005 incidence rates for others are as follows: Campylobacter, 12.71 and 12.72; Shigella, 6.09 and 4.67; Cryptosporidium, 1.91 and 2.95; and E coli O157, 1.31 and 1.06.

To adjust for the increase in the FoodNet surveillance area since 1996, the CDC uses a statistical model to estimate the changes in rates of foodborne infections since the baseline period. Estimated declines include 50% for Yersinia, 35% for Shigella, 34%, for Listeria, and 30% for Campylobacter. Incidences of Cryptosporidium and E coli did not change significantly from baseline.

The incidence of Salmonella infections did not decrease from baseline, though the CDC noted some changes in the serotypes identified: S Typhimurimum decreased significantly (41%), but significant increases were seen for S Enteritidis (28%), S Newport (42%), and S Javiana (92%).

Among the notable changes, the rate of Vibrio infections compared to baseline was up dramatically in 2006 at 78%, compared to 41% in 2005. Of the 147 cases recorded by FoodNet in 2006, 94 (64%) were parahaemolyticus isolates.

Craig Hedberg, PhD, a foodborne disease expert and associate professor of environmental and occupational health at the University of Minnesota in Minneapolis, told CIDRAP News that he didn't see many striking changes in the 2006 FoodNet report. Some of the increase in E coli O157 infections could be linked to the nationwide outbreaks, he said, but other environmental issues could be contributing to the problem.

The higher than normal S Javiana incidence could suggest that there may be some risk related to produce, Hedberg said, noting that the strain has been associated with previous tomato-linked outbreaks.

It's not clear what the higher incidence of S Enteritidis cases means, he said, noting that the predominant phage type is associated with chicken meat, rather than eggs. "Chicken is one of the most commonly eaten foods, so given the widespread consumption, a small problem with food handling, either in the restaurant or in personal kitchens, can translate into larger volume issues," Hedberg said.

CDC. Preliminary FoodNet data on the incidence of infection with pathogens transmitted commonly through food—10 states, United States, 2006. MMWR 2007 Apr 13; 56(14):336-39 [Full text]

See also:

Apr 12 CDC news release

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