Centers for Disease Control and Prevention Morbidity and Mortality Weekly report has summarized epidemiologic data for the 1,097 reported outbreaks occurring during 2007 which resulted in 21,244 cases of foodborne illness and 18 deaths. Among the 497 foodborne outbreaks with a laboratory-confirmed single etiologic agent reported, Norovirus was the most common cause, followed by Salmonella.
Among the 18 reported deaths, 11 were attributed to bacterial etiologies (five Salmonella, three Listeria monocytogenes, two Escherichia coli O157:H7, and one Clostridium botulinum), two to viral etiologies (norovirus), and one to a chemical (mushroom toxin).
Four deaths occurred in outbreaks with unknown etiologies.
Among the 235 outbreaks attributed to a single food commodity, poultry (17%), beef (16%), and leafy vegetables (14%) were most often the cause of illness.
Public health officials from 48 states, Puerto Rico, and the District of Columbia reported 1,097 foodborne disease outbreaks; multistate outbreaks involving two additional states (Montana and Nevada) were reported indirectly.
Norovirus was the most common cause of illness, accounting for 193 (39%) of the confirmed single-etiology outbreaks and 97% of those caused by viruses. Salmonella was the second most common, causing 136 (27%) confirmed single-etiology outbreaks and 53% of those attributed to bacteria. Among Salmonella serotypes identified, Enteritidis was the most common, causing 28 confirmed single-etiology outbreaks with 555 illnesses. Shiga toxin-producing E. coli (STEC) caused 40 of the confirmed single-etiology outbreaks (15% of those attributed to bacteria), of which 39 were caused by serogroup O157.
Foods associated with multistate Salmonella outbreaks included commercially-processed frozen pot pies (401 illnesses, three deaths), commercially-processed vegetable snacks (87 illnesses), eggs (81 illnesses), spinach/lettuce (76 illnesses), beefsteak tomatoes (65 illnesses), raw tuna (44 illnesses), ground beef (43 illnesses), cheese (20 illnesses), alfalfa sprouts (15 illnesses), and raw fresh basil (11 illnesses). Of the six multistate outbreaks of E. coli O157:H7 infection, the vehicle for five was ground beef (117 illnesses) and the vehicle for one was commercially-processed frozen pepperoni pizzas (27 illnesses). The vehicle for the C. botulinum toxin outbreak (eight illnesses) was commercially canned hotdog chili sauce. The one multistate outbreak caused by norovirus was associated with raw oysters (40 illnesses).
Two of the three largest reported outbreaks in 2007 were caused by Salmonella. The vehicles were hummus (802 illnesses) and commercially-processed frozen pot pies (401 illnesses and three deaths).
The second largest outbreak was caused by norovirus at a conference hotel (526 illnesses); several shared food items were the suspected vehicles. The largest outbreaks assigned to a single food commodity were caused be a chicken dish contaminated with C. perfringens (132 illnesses), leafy vegetable salad contaminated with norovirus (128 illnesses), chili beans contaminated with C. perfringens (125 illnesses), and beef contaminated with E. coli O157:H7 (124 illnesses).
Many factors in detection and reporting likely contribute to variation in the annual rate of outbreaks reported by states. However, the emergence of two new norovirus strains in 2006 likely resulted in a relative increase in norovirus outbreaks in 2006 and early 2007. Subsequently, increased population immunity to these new strains might have contributed to the relative decrease in norovirus outbreaks in 2007.
This pattern of emergence of new norovirus strains corresponding with a spike in norovirus outbreaks appears to occur worldwide approximately every 2–3 years. The overall decrease in reported outbreaks in 2007 largely resulted from a reduction in the proportion caused by norovirus. The number of outbreaks caused by bacterial agents in 2007 was similar to the 2002–2006 average.Despite the decrease in 2007, norovirus was still the leading cause of reported outbreaks and outbreak-related illnesses. Norovirus contamination can occur before the point of food preparation and service, as indicated by recent multistate and international norovirus outbreaks associated with oysters, raspberries, and delicatessen meat.
The large number of norovirus foodborne outbreaks indicates a need for continued attention to preventing food contamination by food employees who come into contact with ready-to-eat foods. Norovirus outbreaks are thought to largely result from contamination of food via the unwashed or improperly washed hands of food workers shedding norovirus in their stools. Enhanced food safety training for food employees that work with ready-to eat foods, and the presence of a certified food protection manager in food service and retail establishments, as recommended by the Food and Drug Administration’s (FDA) Food Code,
the results of this analysis represent data available at a single point in time and might differ from those published earlier or subsequently.
Further information on foodborne disease outbreaks, including the Foodborne Outbreak Online Database (FOOD), is available at http://www.cdc.gov/foodborneoutbreaks.
Acting Director of the CDC’s Division of Foodborne, Waterborne and Environmental Diseases Chris Braden said: “Knowing more about what types of foods and foodborne agents have caused outbreaks can help guide public health and the food industry in developing measures to effectively control and prevent infections and help people stay healthy.”