Preventing Norovirus Infection
Norovirus infection can be prevented through attention to proper sanitation and cooking procedures.
The role of food handlers has been documented substantially, highlighting that keeping ill food handlers out of the kitchen coupled with proper handwashing is the best strategy to prevent norovirus.
Outbreaks linked to infected restaurant staff in the past have led to multiple meals served from the same kitchen causing illness. In a 2006 outbreak in Michigan, the investigation revealed that several foodservice workers had been ill and continued to work, ultimately leading to environmental contamination and persistence when a line cook had vomited in the restaurant. At least 364 restaurant patrons became ill with gastroenteritis consistent with norovirus. The investigation also identified deficiencies with employee handwashing practices, cleaning, and sanitizing of food and nonfood contact surfaces.
In 2017, a similar outbreak led to 159 norovirus GII illnesses at a wedding venue in Nebraska over subsequent receptions. Attendees of these events were exposed to norovirus, likely through food and the environment. The investigation singled out at least one employee involved with preparing and serving food who worked soon after being ill themselves, returning to work <24 hours after symptom resolution. The investigation suggested that a combination of contaminated environmental surfaces and infected food handlers likely sustained the outbreak.
Another example of a similar outbreak occurred in Kansas in 2012, where 15 wedding attendees reported symptoms consistent with norovirus GII 12 to 48 hours following the event. Analyses of the food histories did not reveal a single food item significantly associated with illness, but a post-event environmental health investigation highlighted that an ill or asymptomatic individual that helped prepare food for this event could have been the source of this outbreak, as contamination controls were lacking.
The good news about norovirus is that it does not multiply in foods as many bacteria do. In addition, thorough cooking destroys the virus. To avoid norovirus, make sure the food you eat is cooked completely. While traveling in areas that have polluted water sources, raw vegetables should be washed thoroughly before being served, and travelers should drink only boiled drinks or carbonated bottled beverages without ice.
Shellfish (i.e. oysters, clams, mussels) pose the greatest risk, and any particular serving may be contaminated with norovirus; there is no way to detect a contaminated oyster, clam, or mussel from a safe one. Shellfish become contaminated when their waters become contaminated—e.g., when raw sewage is dumped overboard by recreational or commercial boaters. Shellfish are filter feeders and will concentrate virus particles present in their environment. With shellfish, only complete cooking offers reliable protection; steaming does not kill the virus or prevent its transmission. Some researchers suggest that norovirus monitoring in shellfish areas could be a good preventive strategy. Waterborne norovirus outbreaks are ubiquitous, but difficult to recognize. Improved analysis of environmental samples would have the potential to significantly improve the detection of norovirus in shellfish waters.
Finally, and as briefly mentioned earlier, outbreaks of norovirus infections have become synonymous with cruise ships. Healthcare facilities also experience a high incidence of norovirus outbreaks. The CDC has published information regarding the prevention of norovirus outbreaks on cruise ships and in healthcare facilities on its website (https://www.cdc.gov/norovirus/...). Once a case has occurred, even more stringent hygienic measures than normal are required in order to prevent an outbreak, particularly one in an enclosed space such as a cruise ship.
Cleaning and Sanitizing
Studies have highlighted the important role environmental transmission plays in the spread of norovirus, particularly because the virus can remain infectious on surfaces for up to two weeks. Additionally, vomiting incidents play an important role in transmitting norovirus as vomit can contain a very high amount of infectious virus that can then be aerosolized. Norovirus cannot be inactivated by many common cleaning compounds used by schools, including phenolic and quaternary ammonium compounds. The use of these compounds over effective sanitizers, most commonly hypochlorite (chlorine bleach), may make outbreaks worse. Emphasizing the correct sanitizers is extremely important when covering control measures for norovirus as background research indicated that some health officials would recommend ineffective sanitizers.
Handwashing and Hand Sanitizing
Combating the spread of norovirus often requires risk management behaviors, increased hygiene, and cleaning/sanitizing measures. Several studies have highlighted the need for increased education as a means of preventing and controlling norovirus outbreaks.
In schools experiencing a gastrointestinal illness outbreak, there is evidence that control measures, including hand hygiene employed by the school, can be ineffective and lead to a prolonged outbreak. Alcohol-based hand sanitizers, many of which are not effective against norovirus, can exacerbate the spread of the virus.
Proper handwashing was prioritized as a control measure because numerous studies have indicated its value in reducing norovirus spread. The need to implement handwashing over hand sanitizer use was covered numerous times as various studies have shown that hand sanitizers are not effective against norovirus.
Recent Advances in Our Understanding of Norovirus
In 2011, USDA-NIFA funded the NoroCORE Project, housed at NC State University, with a $25 million Coordinated Agricultural Project. The purpose of the project was to increase scientific knowledge of norovirus, and then communicate and translate this information into real world applications that will reduce the burden of disease associated with these viruses. NoroCORE has successfully brought researchers and resources from varied scientific disciplines together, while also providing strong education and outreach programs to a diverse stakeholder group.
The Cultivation of Human Norovirus
One historical challenge of our understanding of norovirus was how difficult it was to handle the virus in a laboratory and that a culture system was not available until recently. This lack of a culture system has long been considered the most significant barrier to norovirus research. Dr. Mary Estes at Baylor College of Medicine (BCM) had success growing human norovirus from human intestinal cells in 2016, as part of the NoroCORE Project. The method has been reproduced in other labs, and scientists all over the world are now beginning to really investigate norovirus control and transfer as opposed to using surrogates.
Although the main routes of norovirus transmission are through consumption, some evidence also suggests the virus may be transmitted through the air. It is possible that infectious particles could be aerosolized from, for instance, vomit or toilet flushing, deposited in the upper respiratory tract during inhalation, and swallowed. Recently, two studies presented evidence of norovirus in hospital air during outbreaks; it was detected in the dust and the air. Such aerosolization is thought to be a particularly important route of norovirus transmission. In closed environments such as cruise ships, schools, hospitals, and restaurants, the plume of viral particles following a vomiting episode can cause or prolong an outbreak, especially when coupled with incorrect sanitizing methods.
In one case study following an outbreak at a hotel in England, environmental samples from mantels and light fittings tested positive for norovirus, suggesting that contamination from aerosolized virus particles may have been a factor.
Investigators at North Carolina State University created a vomiting machine to understand whether the virus is aerosolized when someone vomits and, if so, how much. According to this study, a tiny amount of virus is released into the air after a simulated vomiting event, but it is enough to cause human disease. Coupled with the fact that the resulting aerosol spreads out over several feet, these data suggest that wide areas need to be disinfected after a vomiting event.