With all the attention given to multi-state foodborne disease outbreaks involving Salmonella and E. coli O157:H7, one important microbial source tends to get buried. It turns out these two bacteria are not the most common source of foodborne illness outbreaks in the United States, but rather norovirus is, according to a new report from the U.S. Centers for Disease Control (CDC) examining 2006 data (the most recent available). And the plain truth is foodborne outbreaks of norovirus occur most often when infected food handlers neglect to wash their hands well after a potty break. Also important to note, of the outbreaks that can be traced to a single pathogen and single food, baked chicken contaminated with C. perfringens is the most common. That points to problems with holding temperatures of cooked poultry. So paying attention to good old-fashion sanitation practices in commercial food preparation is still key in preventing future foodborne disease outbreaks.
At the same time, prevention of large multi-state Salmonella and E. coli O157 outbreaks continues to be, and rightly so, a food-related public health priority. These bacteria can cause serious and life-threatening illnesses, sometimes death, often due to secondary complications or diseases. The U.S. Food and Drug Administration (FDA) estimates that two to three percent of all foodborne illnesses lead to secondary long-term illnesses. Certain strains of E.coli (for example, O157:H7) can cause kidney failure in young children and infants; Salmonella can lead to reactive arthritis and serious infections; Listeria can cause meningitis and stillbirths; and Campylobacter may be the most common precipitating factor for Guillain-Barre syndrome.
Foodborne illnesses are a major health burden in the United States, and because most of these illnesses are preventable, analyzing outbreaks helps identify causes and potential controls that could help prevent future outbreaks. Let's take a look at the new CDC analysis published in the June 12, 2009, issue of Morbidity and Mortality Weekly Report. Here's how some of the numbers shake out:
- A total of 1,270 foodborne disease outbreaks (FBDOs) were reported, resulting in 27,634 cases and 11 deaths.
- Among the 624 FBDOs with a confirmed pathogen, norovirus was the most common cause, accounting for 54% of outbreaks and 11,879 cases, followed by Salmonella (18% of outbreaks and 3,252 cases).
- Among the 11 reported deaths, 10 were attributed to bacterial pathogens (six Escherichia coli O157:H7, two Listeria monocytogenes, one Salmonella and one Clostridium botulinum), and one was attributed to a chemical (mushroom toxin).
- The most common foods to which outbreak-related cases were attributed were poultry (21%), leafy vegetables (17%), and fruits/nuts (16%).
- Among the 621 outbreaks (with 18,111 cases) with a confirmed single pathogen, 343 (55%) outbreaks and 11,981 (66%) cases were caused by viruses, 217 (35%) outbreaks and 5,781 (32%) cases were caused by bacteria, 52 (8%) outbreaks with then remaining outbreaks caused by chemicals (1%) or parasites (1%).
- Norovirus caused 337 (98%) of the confirmed FBDOs attributed to viruses.
- Salmonella, the most commonly reported bacterial etiologic agent, caused 112 (52%) of the confirmed outbreaks attributed to bacteria. E. coli caused 29 (13%) of confirmed outbreaks attributed to bacteria, of which 27 were serogroup O157.
- Although dairy accounted for only 3% of single commodity outbreak-related cases (16 outbreaks and 193 cases), 71% of dairy outbreak cases were attributed to unpasteurized (raw) milk (10 outbreaks and 137 cases). A wide range of bacterial pathogens were associated with unpasteurized milk outbreaks, including Campylobacter, E. coli O157, Salmonella and Listeria.
- The largest outbreaks with a known etiology and single food were attributed to baked chicken contaminated with C. perfringens (741 cases), peanut butter contaminated with Salmonella (714 cases), and spinach contaminated with E. coli O157 (238 cases). In the spinach outbreak, 31 persons developed hemolytic uremic syndrome, and five died, including a child. The contaminated spinach was traced back to a single farm, where the outbreak strain was isolated from nearby cattle feces and feral swine feces.
The CDC notes:
While the report provides very useful data, the CDC points out several limitations:
1) Only a small proportion of all foodborne illnesses reported each year are identified as associated with outbreaks. Some foodborne illnesses reported as sporadic cases likely are part of outbreaks not identified as such; also, smaller outbreaks might be reported to public health authorities.
2) Not all recognized outbreaks are reported to CDC. Some outbreaks are not investigated because of competing priorities in health departments.
3) For many reported outbreaks, information on certain aspects, such as the pathogen or the implicated food vehicle, is incomplete.
4) Only about half of the reported outbreaks in 2006 had a confirmed pathogen and thus might not be representative of those with a suspected or unknown etiology.
5) Variations in outbreak detection, investigation, and reporting, make comparisons with previous years difficult.
To ensure safe food from farm to table takes concerted effort, involving training in addition to regulation and legislation. Farmers, ranchers, manufactures, warehouse distributors, retailers, food service establishments, hospitals and schools, are all subject to various regulations and are engaged in food safety practices on an ongoing basis. The FDA as well as industry organizations such as the Grocery Manufacturers Association provide extensive educational and training resources.
Fight Bac!, a campaign from the non-profit organization Partnership for Food Safety, advises four key practices for safe food handling at home:
- CLEAN: Wash hands and surfaces often
- SEPARATE: Don't cross-contaminate!
- COOK: Cook to proper temperature
- CHILL: Refrigerate promptly
The Fight Bac! Web site contains a wealth of useful information, including resources for teachers and an interactive site for children, so check it out! While the campaign screams "bacteria," the same principles apply to other preventing other microbial contamination, from viruses and parasites.
