Norovirus, also known as the stomach flu, is a challenging virus to control. Experts have postulated that it may be near the “perfect” virus. Below are some key features which allow norovirus to continue to circulate despite our best efforts to control infections.
- Noroviruses have a low infectious dose – somewhere in the 10 to 100 particle range. This means people can become sick from ingesting very small amounts of norovirus.
- Noroviruses are non-enveloped. The virus lacks an envelope which allows them to persist in the environment, e.g. water, food, surfaces, much longer than viruses that have an envelope, such as SARS-CoV-2. The lack of an envelope also confers a higher resistance to biocides.
- Noroviruses are transmitted via the fecal-oral and vomit-oral route. This means there are many vehicles by which noroviruses may ingested, such as contaminated foods, water, and transfer from contaminated surfaces.
- Infected people shed norovirus after they feel better. It’s important to understand that while you feel well enough to return to work, you may still be shedding norovirus for up to 30 days (1).
- Norovirus infections confer limited durable immunity. Immunity roughly lasts 6 months to 2 years and that immunity may not be cross protective against other norovirus genotypes (2)
Norovirus Basics
Norovirus is a significant contributor to foodborne outbreaks in the United States, accounting for over 50% of such incidents each year. Norovirus outbreaks occur throughout the year but have a strong seasonality between November and April. There are a variety of noroviruses but only human noroviruses infect humans. So, when a norovirus outbreak occurs we know it is because human fecal or vomitus material was ingested. The uptick in norovirus cases during the winter months is primarily attributed to people spending more time indoors due to colder weather (3).
Norovirus Association with Food
Food handlers play a critical role in safeguarding food from a variety of pathogens. Contamination of hands from the source or from objects is a major route of norovirus transmission in the retail and food service sector. So, technically any food is vulnerable to becoming a vehicle for transmission. However, there is data that suggests certain foods are more associated with norovirus outbreaks. Within the US, leafy greens, fruits, nuts, mollusks, and ready-to-eat food items are some of the top food commodities associated with norovirus outbreaks.
Prevention and Control Mechanisms
To effectively combat norovirus, it is critical to implement a multi-pronged approach. This includes:
- Monitor local health department trends. This is a great way to proactively understand your environment. They can be used as early warning signs. If you notice norovirus outbreaks popping up in your area, then it’s a great time to re-educate staff on basic prevention measures outlined below. The CDC also has a collection of systems for reporting and surveillance.
- Employee Health Monitoring. Preventing employees with symptoms like vomiting and diarrhea, especially those in food-handling roles, from working is a critical step in reducing the risk of norovirus outbreaks.
- Hand hygiene compliance. We use our hands to manage the front-end and back-end of our digestive track. It is critical to keep our hands clean to protect ourselves and others if preparing food.
- Surface Disinfection. Employ an EPA-registered disinfectant with a norovirus claim on the label (it may show up as feline calicivirus on the label). Routine disinfection of hotspots, e.g. restrooms and high touch surfaces is always recommended, but it’s critical to employ this measure when your area is experiencing an outbreak or your organization has had sick employees onsite.
- Report outbreaks to local health authorities. You or your organization may have been hit with an outbreak, but you may help prevent future ones by informing health authorities.
References:
- Duret, Steven, et al. "Quantitative risk assessment of norovirus transmission in food establishments: evaluating the impact of intervention strategies and food employee behavior on the risk associated with norovirus in foods." Risk Analysis 37.11 (2017): 2080-2106.
- Simmons, Kirsten, et al. "Duration of immunity to norovirus gastroenteritis." Emerging infectious diseases 19.8 (2013): 1260.
- Hall, Aron J., et al. "Norovirus disease in the United States." Emerging infectious diseases 19.8 (2013): 1198.
- Norovirus Burden and Trends. Centers for Disease Control and Prevention https://www.cdc.gov/norovirus/burden.html#:~:text=Norovirus%20outbreaks%20occur%20throughout%20the,common%20settings%20of%20norovirus%20outbreaks.