Control of Foodborne Viruses at Retail

Although the number of viruses associated with foodborne outbreaks is relatively small in comparison to their bacterial counterparts, they represent a significant threat to global public health. Moreover, the emergence of novel viruses in food with a greater potential to cause morbidity and mortality suggests that control at the retail level is important. Due to the ability of viruses to persist in the environment and resist many disinfection methods, only a few options are currently viable, yet recent advancements suggest other options may be available in the future. This chapter will provide an overview of the viruses known and postulated to be potential sources of foodborne infection at the retail level, their routes of spread, current regulatory mechanisms in place to prevent infection, as well as explore both proven and new methods for control.

breaks in the USA revealed that regardless of the means of spread, over 40 % of the recorded outbreaks were due to virus infection (Centers for Disease Control and Prevention 2013 ). Globally, estimates suggest that viruses may account for between 8 and 68 % of the total number of foodborne infections (FAO/WHO 2008 ). A signifi cant proportion of these cases are due to the continuing increase in food importation (Centers for Disease Control and Prevention 2013 ; FAO Trade and Markets Division 2012 ). Many of these countries do not have the capacity to incorporate food safety practices including hazard analysis and critical control point (HACCP), good hygiene practices (GHP), and adherence to the standards of the Codex ). Yet, imported foods are actively sought by an increasing exotic appetite in the developed world. Without proper surveillance activity, many viral agents can move freely across borders without detection (Buisson et al. 2008 ;Jebara 2004 ).

Viruses in Food
The diverse nature of the viruses listed in Table 6.1 suggests that each possesses unique physical characteristics, causes a diverse array of symptoms, persists in the host and environment, and has a number of routes for spread. However, they all share common properties that are indicative of the necessary means for control: 1. They are abundant in nature. 2. They are common to several or all areas of the world. 3. They can easily be transferred either through contaminated water or through the fecal-oral route.
Adenoviruses : The adenoviruses are a group of double-stranded DNA viruses that are known pathogens of humans. Most documented cases are respiratory in nature, however, two particular strains, Ad40 and Ad41 have been implicated in gastroenteritis and foodborne transmission in many areas of the globe (Ahluwalia et al. 1994 ;Aminu et al. 2007 ;Brown 1990 ;Bryden et al. 1997 ;Dey et al. 2009 ;Grimwood et al. 1995 ;Herrmann et al. 1988 ;Johansson et al. 1994 ;Saderi et al. 2002 ;Shinozaki et al. 1991a ;Tiemessen et al. 1989 ) particularly in children under 2 years of age (Shinozaki et al. 1991b ;Uhnoo et al. 1984 ). The main source of these viruses is unsafe water, which can either contaminate fi sh or produce through irrigation. For example, Hansman et al. ( 2008 ) identifi ed that 52 % of 33 packages of clams collected from Japanese markets were positive for adenoviruses. Similarly, Cheong et al. ( 2009 ) found the presence of adenoviruses on spinach, lettuce, and chicory; a result of irrigation with unsafe water. Based on laboratory studies of the persistence of these viruses on foods, there was no signifi cant loss of infectivity after 1 week (Verhaelen et al. 2012 ). A similar study by Diez-Valcarce et al. ( 2012 ) showed that 36 % of the mussels sampled from three European countries had the presence of the gastrointestinal adenoviruses.
Aichi virus : First discovered in 1989 (Yamashita et al. 1991 ), this virus is a member of the Picornaviridae family in the Kobuvirus genus. Over the last two decades, the aichi viruses have demonstrated their signifi cance as a foodborne pathogen worldwide (Goyer et al. 2008 ;Jonsson et al. 2012 ;Kaikkonen et al. 2010 ;Oh et al. 2006 ;Reuter et al. 2009 ;Ribes et al. 2010 ;Sdiri-Loulizi et al. 2009 ;Verma et al. 2011 ;Yang et al. 2009 ). The main sources of the virus are unsafe water and sewage (Alcala et al. 2010 ;Di Martino et al. 2013 ;Kitajima et al. 2011 ;Sdiri-Loulizi et al. 2010 ) and production of foods with such waters results in the potential for infection at the consumer level. The virus has been implicated in an outbreak associated with the consumption of oysters (Le Guyader et al. 2008 ) and has been linked to other incidences of gastroenteritis (Oh et al. 2006 ), although the food source was not determined. The virus is stable on produce (Fino and Kniel 2008a ) and in shellfi sh (Sdiri-Loulizi et al. 2010 ).
Astroviruses : This group of viruses found in the Astroviridae family was fi rst described in 1975 by Madeley and Cosgrove ( 1975 ). These viruses are signifi cant pathogens of both humans and animals (Kurtz and Lee 1987 ) and have been identifi ed in human outbreaks associated with foods (Le Guyader et al. 2008 ;Mead et al. 1999 ). The predominant route of infection is water (Abad et al. 1997 ) and the virus can persist on fomites for several days (Abad et al. 2001 ), suggesting that foodborne infections are due to improper food handling. Yet, there has also been evidence that astroviruses can contaminate shellfi sh (Hansman et al. 2008 ), suggesting a possible foodborne route at the retail level.
Hepatitis A virus : Also a member of the Picornaviridae family, HAV is a wellrecognized cause of foodborne disease (Fiore 2004 ;Sanchez et al. 2007 ). The virus is abundant worldwide and present in many regions of the world including developed countries such as Italy (Campagna et al. 2012 ) and The Netherlands (Whelan et al. 2013 ). Studies in the laboratory have shown that HAV is highly stable in the environment (Siegl et al. 1984 ) and can easily be found in shellfi sh growing in contaminated waters (Diez-Valcarce et al. 2012 ). In agricultural settings, the virus can be internalized into produce such as spinach (Hirneisen and Kniel 2013 ), tomatoes (Carvalho et al. 2012 ), and strawberries (Niu et al. 1992 ). While there is ample evidence to suggest that the virus can easily be involved in retail as a result of improper food processing (Wang et al. 2013 ), there is also signifi cant evidence showing that the virus can also be transferred through food handling (Tricco et al. 2006 ). The virus can transfer easily through environmental surfaces, known as fomites (Abad et al. 1994 ) including knives and graters (Wang et al. 2013 ), and can remain infective for several hours in acidic conditions (Scholz et al. 1989 ).
Hepatitis E virus : Initially described as a picornavirus in 1983 (Balayan et al. 1983 ), HEV has been found to represent a novel genus, Herpesvirus (Berke and Matson 2000 ). Since its discovery, the virus has grown to be a major cause of hepatitis in the developing world and its prevalence is growing in the developed world (Miyamura 2011 ). Transmission is generally mediated through water, however, foodborne outbreaks have occurred, primarily through the ingestion of improperly cooked meat products including swine, boar, poultry, venison, ovine, and beef products (Meng 2011 ). HEV has also been found in shellfi sh (Koizumi et al. 2004 ;Song et al. 2010 ), in pig livers (Berto et al. 2012 ;Bouwknegt et al. 2007 ), and in agricultural produce (Ceylan et al. 2003 ), but the risk associated with these two routes is signifi cantly smaller than that of livestock and game meats.
Caliciviruses : The caliciviruses are a group of small viruses that are very stable in the environment and pose a signifi cant threat for foodborne infection. The two major groups of caliciviruses known to cause foodborne infection are the sapovi-ruses and the noroviruses. While sapoviruses have been associated with foodborne outbreaks (Gallimore et al. 2005 ;Kobayashi et al. 2012 ;Usuku et al. 2008 ), noroviruses are the leading cause of gastroenteritis worldwide (Koo et al. 2010 ). The viruses were fi rst discovered in 1972 (Kapikian et al. 1972 ) in an isolated case of pediatric diarrhea. Over the three decades that followed, the noroviruses were found to be globally abundant and identifi ed as the cause of winter vomiting disease, stomach fl u, and cruise ship illness. There have been over 900 documented cases of norovirus foodborne outbreaks (Matthews et al. 2012 ), many of which were determined to be due to retail and RTE purchases.
Rotaviruses : These viruses are part of the Reoviridae family. Studies to identify the presence of the virus in the food supply have revealed its presence in almost every aspect of the food continuum from shellfi sh (Benabbes et al. 2013 ;Bigoraj et al. 2012 ;Boxman 2010 ;Hansman et al. 2008 ;Woods and Burkhardt 2010 ) to livestock (Dalton et al. 2004 ;Mattison et al. 2007 ) to produce (Baert et al. 2011 ;Berger et al. 2010 ;Mattison et al. 2010 ;Serracca et al. 2012 ;Tuan et al. 2010 ) and fruits (Berger et al. 2010 ;Le Guyader et al. 2004 ;Martin-Latil et al. 2012 ;Strawn et al. 2011 ;Verhaelen et al. 2012 ). They have been recognized as a major cause of gastroenteritis, particularly in children (Parashar et al. 2003 ). There are fi ve groups of rotavirus but only three are infectious to humans, Groups A-C. They are known to be highly stable in water, can survive for months in the environment (Fu et al. 1989 ), and for several hours in the air (Ijaz et al. 1985 ) and on human hands (Ansari et al. 1991 ). The majority of cases of infection are due to ingestion of contaminated water, however up to 1 % of foodborne infections are attributable to these viruses (Mead et al. 1999 ).
Emerging foodborne viruses : There have been several viruses that have caused concern with respect to foodborne illness due to the potential for infection from live or dead animals, a process known as zoonotic transmission. These include avian infl uenza, the Nipah viruses, and the coronaviruses, of which SARS is a member. In all three cases, they cause signifi cant clinical infection and have high mortality rates.
In addition, for all three viruses, interaction with live animals or foods associated with these animals at the market has led to human infection. In the case of Nipah virus, infection at retail has come from the sharing of raw date sap (Luby et al. 2006 ;Rahman et al. 2012 ), however the prevalence of these cases is low and isolated to areas where bats are common, such as Bangladesh (Luby and Gurley 2012 ).

Controlling Viruses in Food
The means to control viruses in retail foods in theory should not differ signifi cantly from the methods used to control bacterial infections in these same products. However, there are several unique properties of many foodborne viruses that need to be viewed separately from bacteria. Therefore, no bacterial control studies can be extrapolated to the majority of these viruses.
Structurally, viruses are characterized into two major categories, enveloped and nonenveloped. Enveloped viruses possess an external layer made of both proteins and lipids. The lipids in the envelope can easily be broken down, particularly by soaps, rendering the virus unable to infect, a process known as inactivation (Klein 2004 ). In contrast, nonenveloped viruses have an external protein shell that can resist environmental stressors and many disinfectants (Maillard and Russell 1997 ;Sattar et al. 1989 ). In the context of foodborne viruses, the major contributors to infection, i.e., the astroviruses, Aichi virus, caliciviruses, HAV, and HEV, are all small and nonenveloped. The adenoviruses are also nonenveloped although somewhat larger in size, meaning controlling them may be somewhat easier (Maillard and Russell 1997 ). Only the rotaviruses and the emerging viruses, avian infl uenza, SARS, and Nipah are enveloped.
The survival and persistence of enveloped viruses in the food processing environment is fairly poor. Studies on rotaviruses showed that while the viruses have the ability to sustain infectivity over days in both raw and treated drinking water (Raphael et al. 1985 ;Sattar et al. 1984 ), the virus was rapidly reduced on fomites and hands in a matter of hours (Ansari et al. 1988 ). These data correlate well with the fact that foodborne infections due to rotavirus are limited to shellfi sh and raw produce irrigated with water from unsafe sources (Brassard et al. 2012 ;Le Guyader et al. 2008 ;Mattison et al. 2010 ;Vilarino et al. 2009 ). In contrast, the nonenveloped viruses can survive and spread throughout the entire food continuum from processing (Baert et al. 2008 ;Van Boxstael et al. 2013 ) to storage (Brandsma et al. 2012 ;Butot et al. 2008 ;Shieh et al. 2009 ;Sun et al. 2012 ;Verhaelen et al. 2012 ). Moreover, these viruses are well adapted to survive on hands (Greig et al. 2007 ;Richards 2001 ;Todd et al. 2009 ), increasing the potential for contamination both in processing as well as in preparation (Mokhtari and Jaykus 2009 ).
In determining risk factors associated with virus infections, the European Food Safety Authority (EFSA) published a risk assessment taking into account the survivability and transmissibility of viruses (EFSA Panel on Biological Hazards 2011 ). The breadth of the risks reveals that in order to properly control these viruses, there needs to be a wide-reaching set of control measures implemented in food processing and handling to ensure virus infections are reduced.

Viruses and Current Regulatory Mechanisms
Hazard analysis and critical control points (HACCP) and good hygiene practices (GHP) have been incorporated in many food industries and are generally known to be important in reducing the microbial risk to the consumer (FAO 1995 ;Panisello et al. 2000 ). These practices have been adopted in other environments, including retail, although there has yet to be one specifi c set of standards or guidelines to prevent retail virus infections (Little et al. 2003 ;Mortlock et al. 1999 ). The EFSA suggested (EFSA Panel on Biological Hazards 2011 ) that the use of HACCP to control viruses may not be suffi cient to overcome the stability of viruses as well as their spread. In response, a 2008 joint meeting of the FAO and WHO (FAO/WHO 2008 ) suggested that regulation be focused on fi ve high impact areas of concern involving specifi c combinations of viruses.
The virus-food combinations were determined based on (1) the number of documented cases and/or concerns of high impact public health threats; and (2) laboratory information focusing on virus survival in these food types. They are: 1. Noroviruses and HAV in bivalve molluscan shellfi sh, including oysters, clams, cockles, and mussels. 2. Noroviruses and HAV in fresh produce. 3. Noroviruses and HAV in prepared foods. 4. Rotaviruses in water used for food preparation. 5. Emerging viruses and their associated commodities including avian infl uenza, HEV, Nipah and others, as they are indicated.
In each case, there are subcategories that best characterize the potential for risk, as well as priority areas needed for a proper regulatory framework. They include (1) test development to identify these viruses throughout the food continuum; (2) in-depth assessment of exposure to these viruses not only at the consumer level but also at the worker and handler levels; and (3) an analysis of dose-response relationships.
While the EFSA developed these suggestions in 2008, there has been little progress made, due in part to hurdles occurring in the development of tests to identify viruses. While diagnostic tests continue to improve, there continues to be a large variation in testing results. The reasons for this have been excellently reviewed by Stals et al. ( 2012 ). In addition, while the detection of viruses in different food sources continues to improve, the applicability of these diagnostic tests has been less than favorable. All the viruses identifi ed in these priority areas have relatively low dose responses and thus require a very low detection limit. This requires highly sensitive methods such as the diagnostic tool, polymerase chain reaction (PCR), which identifi es the genetic material of a virus, and the more recently developed lab on a chip, in which not only the genetic material but other pieces of the virus including proteins can be detected (Yoon and Kim 2012 ). However, these are hindered by the requirement for a large sample size to best assess a food source. This challenge has yet to be overcome.
Another signifi cant hurdle deals with the linking of quantitative analysis with qualitative risk assessment. Though genetic material may be found in a food source, there may be no actual link to a viable organism able to cause illness; the virus might already be dead. Thus, any current diagnostic test based on genetic material only gives you an indication of the potential risk associated with exposure to a food.
The determination of these fi ve virus-food combinations has increased the understanding of virus transmission in the food continuum and provided keys to improvements in regulation. Using both data collected from the fi eld as well as controlled experimental data using surrogates, such as the murine norovirus (MNV) and vaccine-strain poliovirus and/or bacteriophage MS2 for HAV (Deboosere et al. 2012 ;Richards 2012 ), a more comprehensive look at how these viruses spread by water, food users, and handlers as well as animals, follows.
Water contamination : The introduction of sewage, manure, and other biosolids into the watershed can contaminate water sources used in food production. Several studies have shown the capability of viruses to survive in sewage (Ehlers et al. 2005 ;Kokkinos et al. 2011b ;Muniesa et al. 2009 ;Sattar and Westwood 1976, 1979Wei et al. 2010 ) even after treatment (Myrmel et al. 2006 ;van den Berg et al. 2005 ;Villar et al. 2007 ) and the association with a risk for foodborne illness (Alcala et al. 2010 ;Ceballos et al. 2003 ;Ceylan et al. 2003 ;Cheong et al. 2009 ;Fiona Barker et al. 2013 ;Kokkinos et al. 2011a ;Mathijs et al. 2012 ;Meng 2013 ;Steele and Odumeru 2004 ;Tierney et al. 1977 ;Ueki et al. 2005 ). The incorporation of management strategies to focus on the use of safe water has thus been identifi ed as a necessary step in improving food safety (Godfree and Farrell 2005 ;Keraita et al. 2008 ;Westrell et al. 2004 ). Yet in many areas of the world, maintaining a safe supply of water can be diffi cult (Alcala et al. 2010 ;Ehlers et al. 2005 ;Kokkinos et al. 2011a ), leaving regulatory offi cials facing a conundrum between the need for production and the maintenance of safety.
Food workers and handlers : Food workers and handlers are an important part of bringing foods to retail; however, these individuals also post a threat to the food, particularly when they themselves are infected with a foodborne virus. One study revealed that norovirus can reach as high as 10 10 virus particles per gram of fecal matter (Atmar et al. 2008 ) while symptoms are being experienced. Lower levels can be found even before symptoms have begun (Gaulin et al. 1999 ) and for several weeks after symptoms have subsided (Gallimore et al. 2004 ). With the infectious dose of this particular virus being less than 100 particles (Teunis et al. 2008 ), the chance for contamination leading to infection is particularly high. Yet the most likely chance for contamination in this case occurs at the foodhandling stage, which is the last step before food products are provided to the consumer. As Michaels et al. ( 2004 ) and Mokhtari and Jaykus ( 2009 ) have both shown, food handlers represent the most likely reservoir leading to high levels of viral contamination and subsequent infections to the consumer.
Zoonotic transmission : While the most recent concerns with zoonotic transmission of pathogens such as avian infl uenza, SARS, and Nipah (Chmielewski and Swayne 2011 ; Guan et al. 2003 ;Smith et al. 2011 ) are due to close contact with live animals, the impact of animals on the contamination of the food supply cannot be understated. For example, the increase in HEV infections has been directly attributed to the zoonotic potential of the virus from swine (Banks et al. 2010 ;Berto et al. 2012 ;Bouwknegt et al. 2007 ;Casas et al. 2011 ;Di Bartolo et al. 2008 ;Fu et al. 2010 ;Leblanc et al. 2010 ;Pavio et al. 2010 ;Scobie and Dalton 2013 ). The presence of the virus not only in the liver of swine, but also their feces, suggests that this particular virus could cause infection either through the traditional fecal-oral route or through the bloodborne route during processing. In contrast, within the context of the viruses identifi ed by the FAO/WHO, there is little evidence to demonstrate the likelihood of HAV or rotavirus infection through a zoonotic route. Additionally, the noroviruses have shown potential, albeit no confi rmed zoonotic route has been documented. Surveillance for noroviruses in animals has revealed that they can harbor human noroviruses (Mathijs et al. 2012 ;Mattison et al. 2007 ) and that without proper handling of animals could lead to transmission of the virus to humans, particularly farmers and food workers. Interestingly, Summa et al. ( 2012 ) have suggested that pet dogs may also serve as a route for infection. While this may not pose a risk for food processing, at the food handling level, where pets may be a part of a food service complement, a potential risk could be implied.

Control Measures
The achievements of HACCP and GHP implementation have aided in the increase of food safety but as seen earlier, there are gaps associated with these regulatory protocols in terms of preventing virus contamination of foods and subsequent foodborne infection. There have been a number of methods tested to inactivate viruses in the food continuum with an emphasis on retail. While each has demonstrated its potential to prevent infection of the consumer, there are still specifi c obstacles that need to be addressed. Moreover, in certain cases, there is little current feasibility for the incorporation of the methods at the retail stage; they are best used during prior steps of the food continuum.
Hand hygiene : The most effective and simplest means of controlling virus transmission is proper hand hygiene. In the context of food safety, the most effective means involves the use of soap for a minimum of 20 s followed by rinsing with water (Todd et al. 2010b ). The use of other hand hygiene products, such as alcohol-based handrubs, may be effective against the majority of foodborne bacterial pathogens but the active ingredient, ethanol, is known to be ineffective against HAV and has limited effi cacy against the noroviruses (Liu et al. 2010 ;Park et al. 2010 ;Sattar et al. 2011 ). While there is validity to the incorporation of alcohol-based handrubs in any food safety environment as a supplement to handwashing, these products cannot supplant regular handwashing.
The use of hand hygiene practices in the food continuum has been investigated (Michaels et al. 2004 ;Todd et al. 2010a , b ) and there is an incorporation of hand hygiene in HACCP and GHP guidelines. Yet the use of hand hygiene measures at all stages of the food continuum continues to be an issue, particularly with compliance (Hoelzl et al. 2013 ;Strohbehn et al. 2004 ;Todd et al. 2010a ). In 2008, for example, Strohbehn et al. ( 2008 ) conducted an assessment of foodservice workers in restaurants, childcare institutions, and facilities providing assisted living for the elderly and schools. In comparison to the Food Code requirements of handwashing, which ranged from 7 to 29 handwashing moments per hour, the results were disappointing. In the context of providing RTE foods, this result suggests that there is a signifi cant risk posed to the consumer. Similar results have been seen in other retail markets such as butcheries, supermarkets, and delis (Tebbutt 2007 ).
In 1999, Armstrong ( 1999 ) developed an integrated hygiene program into food safety management called hygieomics. The program not only dealt with the implementation of hand hygiene into food production and processing practices, but also described means to cope with the problems associated with behaviour, which is a common concern in both the healthcare and food services sectors (Ferguson 2009 ;Gilling et al. 2001 ;Huis et al. 2012 ;Vindigni et al. 2011 ;Whitby et al. 2007 ). The process involved rules and compliance enforcement similar to HACCP, but also demanded an individual commitment to action and the development of a community that is engaged in safeguarding the food supply to achieve both personal and organizational confi dence. Such efforts have been used in the health care fi eld with signifi cant success (Huis et al. 2012 ).
Another means to increase hand hygiene compliance in food workers and handlers is the use of appropriate and consistent training regimens. Hand hygiene training has been used extensively in the health care sector and results have been promising (Pincock et al. 2012 ). In food safety, training has been used but the results have been meager to disappointing (Averett et al. 2011 ;Chapman et al. 2010 ;Lillquist et al. 2005 ;York et al. 2009 ). Reasons for these poor results have been investigated (Green et al. 2005(Green et al. , 2006(Green et al. , 2007Pragle et al. 2007 ) and a combination of factors including high workload, inappropriate staffi ng, lack of managerial support, and personal beliefs have been identifi ed. The clear conclusion, therefore, is that a lack of adherence to hand hygiene is based on behavior, not lack of information.
The issues faced in the food industry are no different from those in the health care fi eld where compliance rates for hand hygiene have never reached 100 %. While there has been no meaningful way to reach that goal, there has been a change in the direction of health care toward a 'patient-centric' viewpoint (Landers et al. 2012 ), whereby hand hygiene is a means to keep patient satisfaction high. This may be a very reasonable way to improve hand hygiene rates in the food industry as focusing on the satisfaction of those who are purchasing foods at retail will help maintain a high reputation and continued returns.
Washing and scrubbing : Vega et al. ( 2008 ) have demonstrated that viruses have the ability to attach to produce through electrostatic forces. Based on their analysis, the use of nonionic detergents as well as high levels of salt was suffi cient to remove viruses from the surfaces of lettuce. This suggests that a salt solution of 1 N NaCl and agitation may be suffi cient to remove the majority of viruses from fresh produce. Similarly, Wang et al. ( 2013 ) have shown that the simple action of scrubbing and peeling is suffi cient to reduce up to 99 % of virus from the surfaces of produce. However, the likelihood of cross-contamination without proper hot water treatment in between items increases signifi cantly. This potential for fomite transmission has been demonstrated for other food preparation activities such as cutting and grating (Wang et al. 2013 ).
Temperature : The use of temperature and pasteurization is an effective means to kill bacteria, however, viruses are signifi cantly more resistant to such temperatures. Bozkurt et al. ( 2013 ) have shown that MNV is very temperature resistant, requiring over 10 min in some cases for a reduction of 1 log at 50 °C. Barnaud et al. ( 2012 ) found a similar requirement for inactivation of HEV in meat products. An internal temperature of 71 °C for 20 min was required to completely inactivate the virus. In a more comprehensive study, Tuladhar et al. ( 2012 ) investigated the thermal stability of viruses by measuring the time required to inactivate by 1 log 10 (90 %). The results showed that 53 °C is inadequate to attain proper food safety for adenovirus, poliovirus, MNV, and adenovirus; the time required was well over 5 min and as long as 15 min for MNV-1. The results were signifi cantly improved at 73 °C, with the required reduction being achieved in less than 2 min. Bertrand et al. ( 2012 ) reviewed the available literature and found similar observations for HAV and astroviruses. The data clearly show that higher temperatures than those used for bacteria are required to attain proper inactivation of viruses. Unfortunately, the use of temperatures above 73 °C in the food continuum can pose a problem in terms of maintaining the aesthetic and organoleptic properties of these foods.
Disinfection : The use of liquid chemical microbicides, more commonly referred to as disinfectants, in the food continuum can be used within a HACCP program including at retail. However, the actual application of these chemicals on food can be problematic due to potential changes in food quality, as well as the potential for improper rinsing leading to residues. Studies investigating the use of nonresidual disinfectants have been undertaken to reduce the levels of viruses on the surfaces of foods and also in waters used in the food continuum. Kahler et al. ( 2011 ) investigated the inactivation of viruses in the presence of monochloramine and found that there is a suffi cient reduction of adenoviruses, coxsackieviruses, and MNV for use in food production and processing. In a similar manner, Su and D'Souza ( 2011 ) investigated the use of water containing 5 % trisodium phosphate (which has a similar activity to hypochlorite) on produce. They found the solution was suffi cient to inactivate over 7 log 10 of MNV after rinsing for 30 s. Fraisse et al. ( 2011 ) investigated the use of peroxyacetic acid against MNV and HAV and found that 100 ppm could reduce MNV on lettuce by 1 log with simple washing. An extended exposure of 2 min reduced the levels of MNV by over 99 %, whereas the reduction of HAV was only 0.7 log 10 .
Pressure : The use of high hydrostatic pressure (HPP) may be used in the processing and packaging stages of the food continuum to help prevent spread at retail. HPP has the ability to reduce the viral load of foods, including complex matrices, while maintaining food quality (Kingsley et al. 2004(Kingsley et al. , 2013. Kingsley has reviewed the literature on the use of HPP and found that all but the Aichi viruses may be inactivated in 5 min by pressures ranging from 400 to 500 MPa (Kingsley 2013 ). However, there has yet to be a fully standardized protocol associated with HPP to ensure proper activity against all viruses. Upon fi nding a harmonized and standard protocol, HPP may see a rise in its use.
UV irradiation : Surface decontamination using ultraviolet (UV) irradiation continues to be investigated, although it has limited use in food processing and preparation. UV light has been known for over a decade to inactivate foodborne viruses (Nuanualsuwan et al. 2002 ) at levels over 0.1 J/cm 2 . Fino and Kniel ( 2008b ) found that UV light at a concentration of 0.24 J/cm 2 was effective at inactivating over 99 % of HAV, Aichi virus, and the human norovirus surrogate feline calicivirus (FCV) on experimentally contaminated lettuce and onions. The use of UV was not, however, applicable to strawberries due to shielding of the virus in the seed pockets as well as the three-dimensional nature of the surface allowing shadowing. Jean et al. ( 2011 ) investigated the use of pulsed-UV light to reduce MNV and HAV on inanimate surfaces. When exposed alone, a 2 s burst consisting of 1.27 J/cm 2 overall was enough to inactivate over 99 % of virus. However, when a complex mixture was used (comprising of 5 % fetal bovine serum), that level was reduced signifi cantly. Thus, this method would likely be suffi cient when surfaces are cleaned on a regular basis.
Ionizing irradiation : As an alternative to UV light, in some countries gamma irradiation is an accepted means of bacterial control in food processing and preparation. The use of 4 kGy has now been accepted by the FDA in the USA for use in ensuring food safety (U.S. Food and Drug Administration 2009 ). However, gamma irradiation is far less effective against foodborne viruses. At 4 kGy, Feng et al. ( 2011 ) have shown that inactivation of MNV is not suffi cient to reduce the virus by more than 3 log 10 on the surface of various produce. In a similar experiment, Espinosa et al. ( 2012 ) showed that 4 kGy was somewhat effective at reducing the levels of poliovirus by at least 1.5 log 10 and satisfactory against rotavirus at levels of 3 log 10 . While there is signifi cant promise for the use of irradiation, both the cost and the requirement for highly trained personnel suggest that this method is not applicable for retail but may be used in prior steps to ensure food safety.

Conclusion
Controlling virus infections at retail continues to be a signifi cant challenge due to the fact that viruses can contaminate food at every level of the farm-to-fork continuum. The widespread nature of viruses in water poses a threat during production and their ease of transmission through the fecal-oral route can lead to inadvertent contamination during processing. Moreover, their relative stability and persistence renders many decontamination efforts useless.
There may be a direction to improving the safety of foods, but the path is iterative and highly systematic. There is little doubt that there needs to be a more integrated Food Safety Management System that spans the entire food continuum and harmonizes with the current practices of HACCP, GMP, and GHP. In Europe, the PathogenCombat project (Jakobsen 2010 ) aims to improve food safety through a combination of quantitative and qualitative risk assessment and subsequent framework development to develop Food Safety Management Systems specifi c to each food continuum.
PathogenCombat could potentially be effective not only due to the quantitative evaluations of risk, but also the inclusion of qualitative parameters including behavior and practice audits, as well as the ability for workers and handlers to register complaints (Jacxsens et al. 2010 ). This essentially holds any food production or service company to a higher standard of performance. For example, Sumner et al. ( 2011 ) examined the nature of food handlers' habits when suffering from vomiting or diarrheal illness. They found that over 11.9 % of these individuals actually worked during their sickness and did not adhere properly to food safety practices. No matter how effective technology might be to identify and inactivate viruses, the lack of adherence on the part of these workers is a risk to the food supply, including those who would purchase food at retail.
To fully combat foodborne viruses, the focus of food safety has to widen to incorporate a One-Heath approach such that it includes all stakeholders, not only microbiologists and inspectors. Much like what is occurring in the health care sector, there needs to be a full commitment from everyone involved in the food continuum to ensure that virus contamination is minimized. There may never be a means to entirely prevent virus contamination of food, yet a combination of quantitative and qualitative practices from farm to fork may leave not only these stakeholders, but also consumers confi dent that the food offered at retail is safe. Cheong S, Lee C, Song SW et al (2009) (2009) (2011)