Norovirus spread by restaurants, say CDC

In the US, most outbreaks of norovirus from contaminated food happen in food service settings, primarily in restaurants, according to a new Vital Signs report from the Centers for Disease Control and Prevention.

The report notes that infected food workers are frequently the source of outbreaks of the "stomach flu" bug, often due to touching ready-to-eat foods served in restaurants with their bare hands.

Ready-to-eat foods are foods that require no additional preparation and include washed raw fruits and vegetables for salads or sandwiches, baked goods, and foods that have already been cooked.

Most people hear about norovirus because it is usually what causes outbreaks on cruise ships, says Dr. Tom Frieden, director of the Centers for Disease Control and Prevention (CDC). But what is "much less well known is that those outbreaks only account for about 1% of all reported norovirus outbreaks."

The leading identified cause of outbreaks from contaminated food in the US, norovirus is very contagious. The stomach bug can cause outbreaks anywhere people get together, anywhere food is served.

Every year, around 20 million Americans fall sick with vomiting and diarrhea from norovirus infection.

The most commonly reported route of transmission for the gastric bug is direct person-to-person spread, followed by foodborne transmission - the focus of the new CDC report.

Norovirus outbreaks in restaurants 'far too common'

"Norovirus outbreaks from contaminated food in restaurants are far too common," says Dr. Frieden. "All who prepare food, especially the food service industry, can do more to create a work environment that promotes food safety and ensures that workers adhere to food safety laws and regulations that are already in place."

The report identifies raw foods such as oysters and leafy vegetables as the most common foods implicated in outbreaks. The CDC advise that food handlers should wear gloves to prevent contamination.

The report offers key recommendations to help restaurants and other food service providers prevent norovirus outbreaks. The recommendations, which bring together the Food and Drug Administration model Food Code and CDC guidelines, include:

• Training food service workers and certifying kitchen managers in food safety.
• Ensuring food service workers practice correct hand washing and use single-use gloves and utensils so they do not touch ready-to-eat foods with their bare hands.
• Putting in place policies that require infected food service workers to stay home until at least 48 hours after symptoms like vomiting anddiarrhea have ceased.

'Businesses should encourage sick workers to stay home'

Report co-author Aron Hall, of the Division of Viral Diseases at the CDC, emphasizes the importance of workers staying home when sick, otherwise they risk spreading the bug to many other people. He suggests businesses should "consider using measures that would encourage sick workers to stay home, such as paid sick leave and a staffing plan that includes on-call workers."

Outbreaks of norovirus are reported at various levels in the US, and the latest CDC report summarizes 4 years of analysis of this data, from 2009 to 2012. Over that period, there were 4,318 reported outbreaks of norovirus, of which 1,008 were from contaminated food, most of which occurred in food service settings such as restaurants and banquet or catering facilities.

The other 3,310 reported norovirus outbreaks were associated with health care settings so were not the subject of this report, which focuses specifically on foodborne outbreaks. The CDC cover information and recommendations about norovirus in health care settings elsewhere.

Of the foodborne outbreaks, 520 were a result of factors contributing to food contamination, with 70% of them implicating infected food workers, and of those, over half (54%) involved food workers touching ready-to-eat foods with their bare hands.

The CDC also analyzed which foods and food preparation processes were most commonly implicated in norovirus outbreaks.

In 324 outbreaks where a specific food item was implicated, over 90% became contaminated during the last stage of preparation (for example, making sandwiches using raw or already cooked ingredients), and 75% involved raw foods.

Fruits, leafy vegetables and oysters most mentioned single raw foods

In these outbreaks, the most commonly mentioned single raw foods were fruits, leafy vegetables and molluscs such as oysters.

The CDC note that outbreak report rates vary greatly among states - more than likely due to differences in surveillance efforts rather than a reflection of the real underlying rates of infection. This suggests a need to strengthen health authorities' capacity to investigate and report outbreaks of norovirus, says the agency.

In September 2013, Medical News Today learned how a team of UK scientists showed that copper surfaces rapidly destroy norovirus. Researchers from the University of Southampton found that various copper alloy surfaces rapidly kill norovirus in such a way that there is no chance of mutation leading to emergence of potential copper resistance.

Written by Catharine Paddock PhD

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