2010-2012 Subcommittee: Control Strategies for Reducing Foodborne Norovirus Infections
- Dr. V. Kelly Bunning, Chair
- Dr. Uday Dessai, Chair
- Dr. Wafa Birbari
- Dr. Dan Engeljohn
- Dr. David Golden
- Ms. Susan Vaughn Grooters
- Dr. Margaret Hardin
- Dr. Dallas Hoover
- Dr. Lee Johnson
- Dr. Nandini Natrajan
- Dr. Robert Tauxe
Many viruses can be transmitted by contaminated foods and subsequently cause disease in humans. Human noroviruses (HuNoVs) are now recognized as the leading cause of foodborne disease in much of the developed world. The Food Safety and Inspection Service (FSIS), the Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), the National Marine Fisheries Service (NMFS), and the Department of Defense Veterinary Service Activity (DoDVSA) believe a unified approach to reducing illness from HuNoVs is essential. These agencies issue this charge to NACMCF because:
- HuNoVs are the most commonly identified cause of foodborne outbreaks in the United States;
- information gaps exist for the overall burden of disease, different transmission pathways, and most importantly, contamination routes; and
- improving the ability to control the transmission of HuNoVs through food is critical to the public health.
HuNoVs, and the less prevalent, but related human sapoviruses, are members of the Caliciviridae family. Members of this virus family are the leading cause of acute gastroenteritis (AGE) worldwide. Symptoms usually last for 1 to 3 days, and include nausea, acute-onset vomiting, and watery non-bloody diarrhea accompanied by abdominal cramps. Virus particles are shed in high numbers in the stool and vomit of infected people. Pre-symptomatic, asymptomatic, and recovering persons can shed viruses for days to weeks. Transmission can occur through several routes, including: i) direct person-to-person contact with shedders, ii) exposure to aerosolized vomitus, iii) consuming HuNoV contaminated foods or liquids, and iv) touching contaminated surfaces or objects followed by placing hands in the mouth.
Based on the most recently published data from the CDC electronic Foodborne Outbreak Reporting System (eFORS), 337 (54%) of 624 foodborne outbreaks with a confirmed etiology were attributed to HuNoVs. The 2002 to 2006 eFORS data from 6 states showed that 220 (53.8%) of the 409 confirmed or suspected foodborne HuNoV outbreaks were associated with restaurants, 55 (13.4%) were associated with private settings, 41 (10.0%) were associated with schools and workplaces, and 5 (1.2%) were associated with hospitals and nursing homes. During the same five-year period, there were 1,475 non-foodborne HuNoV outbreaks reported in these states, of which 1,170 (79.3%) occurred in nursing homes. These data help to characterize the relative importance of different HuNoV transmission routes, but more information is necessary to understand the multiple routes of HuNoV transmission and their association with different types of facilities where food is prepared or served.
The USDA Food and Nutrition Service (FNS) Office of Food Safety monitors the safety of food served in the National School Lunch Program. FNS identified HuNoVs as the leading cause of reported outbreaks of foodborne illness in schools based on analysis of eFORS data. From 2005 to 2008, 50% of foodborne outbreaks of known etiology associated with schools were attributed to HuNoVs. School settings present unique risk factors for virus transmission because of the particularly close contact among children, the use of common restroom facilities, exposure to common toys and other fomites, and the sharing of foods. Recent changes in food handling practices in schools, such as the movement to encourage salad bars in school cafeterias, may impact HuNoV transmission.
The food vehicles most commonly associated with foodborne HuNoV outbreaks include molluscan shellfish, sandwiches, salads, and fresh produce. Dairy products and delicatessen meat have also been implicated in outbreaks. Data collected by the CDC, recent publications, and a Center for Science in the Public Interest (CSPI) study on foodborne outbreaks indicated HuNoVs are the most common microbial hazards linked to outbreaks associated with fresh produce (i.e., fresh fruits, vegetables, and salads). In fact, CSPI data have shown that nearly 25% of all produce-associated outbreaks are associated with HuNoV contamination of lettuce and salad greens. Although foods are often contaminated at the point of service, HuNoVs may be introduced to food vehicles further up the food distribution chain, such as during production, harvest, or processing.
The 2009 FDA Food Code specifies preventive controls to reduce the survival and transmission of pathogens in foods prepared and sold in retail and foodservice settings. These preventive controls become regulatory mandates for the retail food industry when adopted by state, local, and tribal authorities that license and inspect these facilities. Since the first edition of the Food Code in 1993, requirements that address the control of HuNoVs and other pathogens have been reviewed and updated as scientific information and best practices have advanced.
Charge Questions for the Subcommittee
The epidemiological evidence clearly indicates that HuNoV infection is both common and difficult to control. Progress in reducing foodborne transmission of HuNoVs requires careful review of our current understanding of its epidemiological significance, transmission, and control. The specific charge to the Committee is to consider the following questions during its deliberations:
- What is known about the incidence and public health burden of HuNoV infection in the United States and in other developed countries? Are there population subgroups at increased risk of more severe disease? Please consider in your response:
- the value of improvements in compliance with the CDC National Outbreak Reporting System (NORS) in an effort to increase HuNoV outbreak reporting for the purposes of characterizing differences in mode of transmission. What is the relative importance of the various transmission routes, including foodborne, in the burden of HuNoV disease in the United States?
- the information gaps for which additional epidemiological or microbiological research or improved public health surveillance might help in controlling foodborne transmission of HuNoVs; and
- the benefit of a sequence-based strain subtyping method (for example the information collected by the CDC CaliciNet initiative). What additional information could be collected to increase the value of the CaliciNet system? For instance, what would be needed to use CaliciNet to determine whether HuNoV genotypes vary as a function of route of transmission or specific food vehicle(s)?
- Which types of foods can be attributed to foodborne HuNoV infections? How common is HuNoV contamination in various foods before they reach final preparation and point of service (i.e., during production, harvest, and processing)? What are the most likely mechanisms of such contamination?
- Are there conditions or food matrices for which the current minimum cooking temperatures in Part 3-4 of the FDA 2009 Food Code might be inadequate for destruction or inactivation of HuNoVs? What temperature must molluscan shellfish be heated to in order to inactivate HuNoVs and is this temperature reached when the product is prepared in traditional ways such as steaming for culinary (but not food safety) purposes? Is foodborne transmission of HuNoVs affected by the holding temperature of food? Does recontamination of cooked foods present increased risk for transmission? Considering only preparation and point of service, how likely is food to be contaminated at this phase?
- What factors most significantly affect the efficacy of removal and/or inactivation of HuNoVs from surfaces and hands when using common cleaning and sanitizing practices? What is known about HuNoV survival, persistence, and transfer on and between foods and surfaces? Are there any concerns about HuNoV survival on surfaces that have been subject to the minimum cleaning and sanitization requirements specified in 4-6 and 4-7 of the FDA 2009 Food Code?
- What methods exist for the detection of HuNoVs in foods and environmental samples and what are the limitations of these methods? How should the issue of virus infectivity be approached when using molecular-based assays? What is the potential for a standard method to be developed and used? What is the value of existing and emerging cultivable surrogate viruses for studying methods development, virus persistence and inactivation, sanitation efficacy, etc.?
- What interventions are available, or might be available in the near future, to reduce or eliminate the likelihood of HuNoV contamination for at-risk foods? Please consider interventions based on:
- Separating ill or infectious persons (including asymptomatic) from foods/time interval for when ill food workers can return to work;
- Reducing contact with contaminated hands;
- Cleaning and sanitizing hands and food contact surfaces;
- Using appropriate procedures in response to incidents of vomiting or diarrhea that occur at food establishments;
- Focusing on interventions upstream from final preparation and point of service.
- Discuss the possible impact and burden of HuNoV illness if the preventive controls such as those specified in the Subparts 2-2, 2-3, and 3-3 of the FDA 2009 Food Code for retail operations were also required of producers and processors of ready-to-eat foods.
- What data are available, and what data are still needed, to conduct a formal quantitative microbial risk assessment of HuNoV transmission in high-risk commodities? Please take into account exposure (levels/frequency) and dose response. When addressing exposure, consider the potential (if any) for zoonotic and secondary transmission of HuNoVs.
- Do certain types of facilities, such as schools, long-term care facilities, restaurants, cruise ships, airplanes, or carriers of foods in interstate conveyance, require a specific HuNoV control strategy? If this need exists, the Committee should develop a generic plan by which to control HuNoV transmission in restaurants and institutions that could be used as a template upon which facility-specific plans could be based.