Colorado State University Extension
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Norovirus Outbreak Hits CSU Extension Staff
Edited by: Mary Schroeder, M.S., R.D. & Pat Kendall, Ph.D., R.D., Colorado State - Winter 2004
Foodborne illness can strike anywhere, as those attending the Colorado State University Extension Fall Forum this October unfortunately experienced. The setting was a workshop sponsored by the Food Science and Human Nutrition Department complete with box lunches delivered to the group by a local deli. The lunches were nutritious and attractive, consisting of turkey or spinach wraps with guacamole, fresh sprouts, a side of lettuce, a fruit cup, raw carrots and dip, and a pickle spear.
The problems started the next morning when some of the Extension agents began to experience headaches, nausea and diarrhea. By the end of the day so many were ill that one of the workshops scheduled for the following day was cancelled. Because only those who had attended the nutrition workshop seemed to be experiencing symptoms, the coordinators of the workshop called the Larimer County Health Department.
The health department followed up with personal or telephone interviews with 20 of the 22 individuals who attended the workshop; 15 (75%) met the case definition (consumed box lunch) and were considered as being ill (defined as having 4 or more of the following symptoms: muscle aches, chills/fever, headache, nausea, vomiting, diarrhea, fatigue and cramps). All symptoms were classic for Norovirus gastroenteritis. The average incubation period for all Forum cases was 40.5 hours, with a range of 18 to 94 hours. Duration of illness ranged from 7 to 72 hours. Also, though no food samples were collected by the health department for laboratory testing, the turkey wraps had the highest calculated attack rate.
In its investigation of the suspect deli, the health department identified three food workers who admitted to recent gastrointestinal illness in the days prior to preparing the implicated lunches. Also, reports of illness with similar symptoms were discovered among four of seven other groups that had ordered boxed lunches on the same day.
Most foodborne outbreaks of norovirus illness are likely to be caused by direct contamination of food by a food handler immediately before its consumption. Noroviruses are transmitted primarily through the fecal-oral route, so inadequate handwashing is often to blame. As a result of the Fort Collins incident, deli management was instructed to meet with all employees to discuss personal hygiene and sick policies and to review proper handwashing and glove use in the establishment.
Disease Burden of Norovirus GastroenteritisThe Centers for Disease Control and Prevention (CDC) estimate that 23 million cases per year of acute gastroenteritis are due to norovirus infection. It is now thought that at least 50% of all foodborne outbreaks of gastroenteritis can be attributed to noroviruses. Outbreaks have frequently been associated with consumption of cold ready-to-eat foods, including salads, sandwiches, and bakery products, as appears to be the case in the CSU incident.
Noroviruses are highly contagious. It is thought that as few as 10 viral particles may be sufficient to infect an individual. In addition, viral shedding may occur from the onset of symptoms and continue for two weeks after recovery. The incubation period for norvirus-associated gastroenteritis in humans is usually between 24-48 hours, but cases can occur within 12 hours of exposure. Symptoms usually last 24 to 60 hours. Recovery is usually complete and there is no evidence of any serious long-term complications.
Diagnosis of NorovirusMany health departments are becoming equipped to perform norovirus testing using reverse transcriptase polymerase chain reaction (RT-PCR). This technique can be used to test stool and emesis samples taken within 48 to 72 hours after onset of symptoms. In the case of the CSU outbreak, two stool samples collected did test positive for Norovirus.
Norovirus WebsiteA very good resource for more information on noroviruses is the CDC's Norovirus website. It includes information on Norovirus and Food Handlers, a Q & A section and fact sheet. Additionally, the site includes a 24-page publication called "Norwalk-like Viruses: Public Health Consequences and Outbreak Management." Go to Norovirus Website.
Sources:- Larimer County Department of Health and Environment Investigation Report: Foodborne Norovirus Outbreak Investigation of Food Science & Human Nutrition Fall Forum, October, 2003.
- Center for Food Safety and Applied Nutrition Bad Bug Book: The Norwalk Virus Family.
- Center for Disease Control and Prevention MMWR Recommendations and Reports. Norwalk-Like Viruses: Public Health Consequences and Outbreak Management. June 1, 2001; Vol.50; No.RR-9.
