Norovirus, Salmonella hold lead roles in US foodborne outbreaks

Sep 8, 2011 (CIDRAP News) – In its annual report on foodborne disease outbreaks, the US Centers for Disease Control and Prevention (CDC) said today that in 2008, norovirus was the most common confirmed cause and that poultry topped the list of implicated food commodities.

The report, which appears in Morbidity and Mortality Weekly Report (MMWR), compiles cases from 2008, the most recent year for which data are complete. In last year's report for 2007, norovirus was also the most commonly implicated cause, and poultry was the most frequently listed commodity.

The CDC's profile for 2008 shows a total of 1,034 outbreaks, with 23,152 cases and 22 deaths. Compared with the average for the previous 5 years, the number of outbreaks was 10% lower and the number of related illnesses was 5% lower, according to the report.

Outbreaks linked to a single pathogen totaled 479, with norovirus responsible for 49% of outbreaks and 46% of illnesses. Salmonella was second most common, blamed for 23% of outbreaks and 31% of infections.

There were 218 outbreaks linked to single food commodities, led by poultry (15% of outbreaks), beef (14%), and finfish (14%). By number of outbreak illnesses, leading the commodity list were fruits and nuts (24%), vine-stalk vegetables (23%), and beef (13%), the CDC said.

The pathogen-food combination linked to the most outbreaks was norovirus in leafy vegetables (18), while the pair blamed for the most illnesses was Salmonella in vine-stalk vegetables (1,604), followed closely by Salmonella in fruits or nuts (1,401).

Seventeen multistate outbreaks were reported in 2008, with nine linked to Salmonella. A responsible agent was isolated from an implicated food in six of those outbreaks, which involved cantaloupe, cereal, ground turkey, ground white pepper, jalapeno and Serrano peppers, and peanut butter and peanut paste.

Six multistate outbreaks were caused by Escherichia coli O157:H7, with the pathogen isolated from ground beef in two of them. Public health officials connected Listeria to two multistate outbreaks, one linked to Mexican-style cheese made from pasteurized milk and one to sprouts.

In an editorial note, the CDC said the commodities linked to the largest number of foodborne illness outbreaks—poultry, beef, and finfish—have not changed over the past decade. It said the numbers of Salmonella Enteritidis and E coli O157:H7 outbreaks are running well above its Healthy People 2010 targets.

Several large multistate outbreaks made vine-stalk vegetables, fruits and nuts, and beef the leaders in causing outbreak illnesses, the report says.

The 2008 data show that Salmonella was the leading cause of outbreak-related hospitalizations and deaths and was the culprit in more than half of the year's multistate outbreaks. However, the CDC said several measures are under way to reverse the trend, including new Food and Drug Administration (FDA) shell-egg regulations that took effect in 2010 and new US Department of Agriculture (USDA) performance standards that lower Salmonella limits for young chicken and turkey carcasses, which took effect in July.

Norovirus still poses outbreak problems, because outbreaks often involve more than one food, the CDC said. Many outbreaks stem from contamination during food preparation by sick workers who haven't properly washed their hands.

CDC. Surveillance for foodborne disease outbreaks, United States, 2008. MMWR 2011 Sep 9;60(35):1197-202 [Full text]

See also:

Aug 12, 2010, CIDRAP News story "Norovirus, poultry leading culprits in US foodborne outbreaks"

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