Viruses cause more than 67% of all food-borne illnesses worldwide (21
). Human norovirus is a major enteric food-borne virus that is a significant problem in foods due to its small infectious dose (<10 particles) and its high stability in the environment (20
). It is estimated that at least 90% of acute nonbacterial gastroenteritis outbreaks can be attributed to norovirus infection, but this number may even be underestimated due to the large number of unreported infections and the lack of methods for rapid detection of the virus (17
). According to a recent report from the Centers for Disease Control and Prevention, approximately 48 million people suffer from norovirus-induced gastroenteritis each year in the United States, there are 128,000 hospitalizations, and 3,000 people die from norovirus each year (12
). Outbreaks of human norovirus are common in any environment where people are in close contact, such as cruise ships, restaurants, hotels, schools, the military, nursing homes, and hospitals (1
). Transmission of norovirus is primarily by the fecal-oral route, either by person-to-person spread or by ingestion of contaminated food or water (13
). The primary symptoms of human norovirus infection include diarrhea, vomiting, fever, chills, and extreme dehydration. It has been a challenge to work with human norovirus since it does not propagate in cell culture and there is no suitable animal model for the virus (19
). For this reason, studies of human norovirus must rely on surrogates such as murine norovirus 1 (MNV-1) or feline calicivirus (FCV) (2
). Because of these challenges, human norovirus and other caliciviruses are classified as category B priority biodefense agents according to the National Institute of Allergy and Infectious Diseases (NIAID).
Fresh produce is at a high risk for contamination by norovirus because it normally undergoes little or no processing and can be contaminated at any step from preharvest to postharvest. According to recent outbreak data, fruits and vegetables are major vehicles in the transmission of food-borne illness (8
). It has been reported that norovirus accounted for more than 40% of outbreaks in fresh produce from 1998 to 2005 in the United States (18
). These outbreaks of norovirus have occurred in lettuce, tomatoes, melons, strawberries, raspberries, fresh cut fruits, and other vegetables (10
). One major route with a high probability of contamination is the use of contaminated water for irrigation or washing. Contamination may also be caused by infected workers handling the food during harvesting, processing, or distribution (10
). With an increasing number of people striving to eat healthier by increasing their consumption of fruits and vegetables, this has become a major public health concern (4
). However, while numerous studies of bacterial contamination of fresh produce to have been reported date, knowledge about viral contamination of fresh produce remains limited.
In current industry, fresh produce usually undergoes a brief sanitization step after harvest from the field. Unfortunately, current commonly used sanitizers are relatively not effective in removing viral contaminants from fresh produce (2
). The most common sanitizer, a solution containing 200 ppm of chlorine, typically only gives a <1.2-log virus reduction in fresh produce (3
). Recently, Baert et al. (2009) found that tap water washing only gave an average reduction of 0.94 logs in shredded lettuce, while the addition of 200 ppm of sodium hypochlorite only led to an additional 0.48 logs, and the addition of 80 ppm of peroxyacetic acid brought about a reduction of only 0.77 additional logs (3
). Therefore, there is an urgent need to develop a more effective sanitizer for removal of noroviruses from fresh produce.
Surfactants are surface-active compounds that can reduce the surface tension of a liquid. The addition of surfactants in a washing procedure will make the liquid spread more easily and lower the interfacial tension between the two liquids or between a liquid and a solid. In addition, they may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants (6
). Surfactants contain both a hydrophilic group and a hydrophobic group, which interact with the substance they are mixed with in order to alter the surface properties of the water either at the water-and-air interface or at the water-and-solid interface (6
). Because of these properties, surfactants allow the release of tightly bound contaminations such as food-borne pathogens from the surface, which leads us to hypothesize that surfactants may enhance the removal of food-borne pathogens from fresh produce. Out of numerous ionic (anionic or cationic) and nonionic surfactants, we chose sodium dodecyl sulfate (SDS), polysorbates (such as Tween 20, Tween 65, and Tween 80), Triton X-100, and NP-40 for the following reasons: (i) SDS is an anionic surfactant and an FDA-approved food additive (FDA 21 CFR 172.822), (ii) polysorbates are a class of nonionic surfactants and GRAS (generally recognized as safe) substances recognized by the FDA (21 CFR 172.840, 172.836, and 172.838), and (iii) Triton X-100 and NP-40 are two other widely used nonionic surfactants that may have similar effects in enhancing sanitization, although there is no record as to the safety of these two surfactants in the FDA Code of Federal Regulations to date.
Here, we report a systematic evaluation of the effectiveness of surfactants in removal of viruses from fresh produce, using murine norovirus 1 (MNV-1) as a surrogate. We found that surfactants alone or a combination of surfactants (at low concentrations) with chlorine solution significantly enhanced the removal of MNV-1 from fresh produce. Using this strategy, >3-log reductions in virus titer were achieved in either fruits (strawberries and raspberries) or leafy greens (cabbage and lettuce). These results strongly support the idea that the combination of a surfactant and chlorine solution is a novel and feasible approach for enhancing the safety of fresh produce.