Fruits and vegetables as a source of microbial disease transmission

Fresh fruits and vegetables are essential parts of both a balanced and healthy diet, and eating of these foods is encouraged by numerous government organizations worldwide. This is because they can stave off a variety of diseases like cancer and cardiovascular conditions (Westrell et al., 2009). However, fruits and vegetables, particularly leafy green vegetables that are ingested raw, are increasingly becoming recognized as important vectors for the spread of human infections that were previously only associated with foods of animal origin (Westrell et al., 2009). In spite of the rising significance of fresh produce as a conduit of human pathogens, there is presently inadequate knowledge regarding where contamination occurs in the supply chain or regarding the means by which human pathogens inhabit and live on or in vegetables and fruits. This review seeks to examine current knowledge and potential future advancements in this increasingly significant area of food safety.
Epidemiology
Over the past years, public health campaigns for lifestyles that are healthy have resulted in growing demand for fresh produce in several developed countries (Gerner-Smidt et al., 2006). Thus, for instance, in the US, the fresh produce industry has reacted with improved local production, enhanced importation as well as enhancements in maintenance of the quality of produce for a longer time. In many parts of the world, fresh produce like salads and fruits are often eaten raw-increasing the risk of infecting consumers by contaminating organisms (Gerner-Smidt et al., 2006).
Consequently, the fresh produce industry in several industrialized countries has reacted by adopting different risk management practices developed to minimize any possible contamination. In spite of this, nonetheless, the number of reported cases associated with contaminated fresh produce has gone up in the US. Such developments in agricultural processing as well as distribution processes aimed at enhancing both the range and supply if products (for instance triple-cleaning pre-packaged leafy vegetables) might also have raised the risk of for more prevalent outbreaks (Westrell et al., 2009).
Thus, in 2007, for instance, Salmonella was discovered in about 0.3 percent of produce-linked samples tested in the European Union. Consequently, in 2007, big studies on incidence of pathogenic bacteria in leafy vegetables and fruits were done in Ireland, the Netherlands, the UK and Germany (Westrell et al., 2009). Thus, the percentage of produce samples which indicated Salmonella in this research ranged from 0.1 percent to 2.3 percent, with pre-cut products having some of the biggest percentages contaminated (Westrell et al., 2009).
Moreover, the proportion of sprouted seed samples that yielded Salmonella was found to be 1.5 percent in the Netherlands and 2.2 percent in Germany whereas 0.4-0.5 percent of spice and herb samples from the UK, Hungary and the Netherlands yielded Salmonella. On the other hand, in 1970s, the percentage of all food-borne outbreaks linked to raw produce in the US, grew from 0.7 percent to 12 percent in 1990s. Many factors have led to these growths, constituting an enhancement in detection (Gerner-Smidt et al., 2006).
New standard sub-tying methods for Escherichia coli O157 and Salmonella have been circulated to all the 50 states in the US over the past 10 years. Normally, public health laboratories present their molecular subtype patterns via electronic means to PulseNet-the countrywide molecular observation network for enteric infections. A system such as this one has noticeably enhanced the capability of detecting outbreaks, particularly those with cases that are scattered widely, as well as identifying their origin (Gerner-Smidt et al., 2006). Nonetheless, there is also a possibility that the recorded rise in the number of sicknesses linked to consuming fresh produce mirrors an exact growth in contamination (Westrell et al., 2009).
Investigators are faced by numerous challenges, chief amongst which is identification of produce item as a causative agent of an outbreak as well as determining the contamination mechanism. Patients frequently do not recall properly the consumption of certain produce items and might not be able to differentiate between different produce items. Furthermore, produce is also frequently eaten as a mixed food item, for instance, mixed leaf or fruit salad, identifying a specific item as the source of infection complication (Gerner-Smidt et al., 2006).
Even in instances when an epidemiologic examination can make out a produce item as an infection conduit; tracing the origin can be hard, because of restricted labeling, product mixture from various farms, distributors, discarded or incomplete records and growing globalization of produce circulation (Centers for Disease Control and Prevention, 2008). In 1995, for instance, Salmonella serovar Stanley infections outbreaks were simultaneously identified in Finland and USA with the causative agent being alfalfa sprouts. The inoculum source for both was believed to be seeds that had been contaminated from a Dutch shipper which might have gotten them from either of 2 continents (Centers for Disease Control and Prevention, 2008).
Bacterial pathogens are believed to a leading contributor of produce-linked food borne sicknesses. Thus, in a 1973-1997 US review of produce-linked outbreaks, it was discovered that bacteria accounted for 60 percent of outbreaks whereby etiologic agent detected. Salmonella was the most common causative bacterial pathogen responsible for almost 50 percent of the outbreaks because of bacteria (Donnan et al. 2011).
A wide range of produce conduits have been linked to salmonella infections. Numerous big-scale outbreaks have been associated with melon and tomato consumption. Serrano and jalapeno, in 2008 were conduits for a big multistate Salmonella serovar Saintpaul outbreaks (Centers for Disease Control and Prevention, 2008).
Other prominent Salmonella enterica outbreaks associated with ready-to-consume plant produce comprise outbreaks in the UK and Scandinavia of serovar Thompson infections linked with rocket leaves consumption (Nygard et al., 2008). Other outbreaks include serovar Anatum infections in Denmark associated with basil that had been imported (Nygard et al., 2008).
In addition, produce-linked E. Coli 0157 infections outbreaks have been increasingly reported and been associated with eating of green leafy vegetables (Friesema et al., 2008). One particular outbreak that was linked with eating of pre-packaged spinach happened in 26 states of the US in September 2006, leading to 3 confirmed deaths and 183 confirmed infections (Grant et al., 2008). Nonetheless, the biggest outbreak of E. coli to date took place in Sakai City, Osaka Japan in 1996 and was traced to white radish sprouts consumption (Michino et al., 1999).
Outbreaks In Australia
In the past two decades, there has been 5 food borne outbreaks related to fresh produce which met the inclusion standards in Australia. Thus, 2 out of these outbreaks are linked to imported produce, imported semi-dried tomatoes were linked with a big multistate Hepatitis A outbreak and baby corn imported from Thailand was linked with a big outbreak of shigellosis (Donnan et al. 2011). Although the source of contamination for the soiled imported produce was not known, however poor sanitation was named as potential source of contamination for the baby corn (Donnan et al. 2011).
The other three outbreaks were linked to rockmelon that had been produced locally (Munnoch et al. 2009), honeydew melon as well as papaya (Gibbs et al. 2009). The 2006 Salmonella Saintpaul outbreak was microbiologically associated to rockmelons that grow and are processed in the Northern Territory (NT). In addition, Queensland rockmelons were discovered to be contaminated with non-outbreak linked strains of Salmonella spp. Definitely, the outbreak strain could not be associated with farming , packing or processing machines.
Nevertheless, investigations of the 6 processing machines situated at Queensland and NT found serious food safety issues not only with the production but also processing of rockmelons which could have added to the contamination of food; consisting the utilization of untreated or insufficiently treated water on ready-to-consume melons, the inappropriate utilization of disinfectants, temperature disparities between wash and fruit water as well as damaged fruit processing (Munnoch et al., 2009).
Likewise the utilization of untreated water and wrong use of chemical disinfectants was cited as another potential cause of fruit contamination resulting to the papaya linked to the outbreak of salmonellosis in Queensland and Western Australia (WA) from October 2006-january 2007. Regrettably, there exists no observations or data that offer details at the potential methods of melon contamination that resulted to the 2010 L. monocytogenes outbreak in Queensland, New South Wales (NSW) and Victoria (Persely, 2010).
Table 1 showing a summarized version of selected global food borne outbreaks due to contaminated produce items (Lynch et al., 2009).
Year Pathogen No of cases No of countries Regions Affected Foodstuff Implicated
2006 Salmonella Thompson 20+ 3 Europe Ruccola (arugula) 2006 Escherichia coli O157:H7 206 2 North America Fresh spinach
2007 Salmonella Weltevreden 45 3 Europe Alfalfa sprouts 2007 Shigella sonnei 175 2 Australia, Europe Raw baby corn
2007 Salmonella Senftenberg 51 5 Europe, North America Fresh basil 2008 Salmonella Saintpaul 1442 2 North America Fresh peppers, tomatoes

Pathogens responsible for the outbreaks
Attachment is one requirement for colonization as well as consequent transmission of pathogens through the edible parts of fruits and vegetables. In fact, on attachment it is very hard to eliminate the pathogens from fruits and vegetables by washing. The following are the most common pathogens responsible for transmission of microbial diseases (Lynch et al., 2009).
Salmonella
Salmonella genus consists of two species: S. bongori and S. enterica (Su and Chiu, 2007. S. enterica is further divided into hundreds of serovars and is a foremost cause of gastroenteritis (Lan et al., 2009). Salmonella is also the pathogen that is most often associated with fruit and vegetables consumption with S. enterica serovars colonizing seeds, sprouted seeds, fruits as well as leaves of a wide range of plant species (Lynch et al., 2009).
Escherichia coli
On the other hand, Escherichia coli happens to be the most common bacteria of the aerobic gut normal flora. Nevertheless, numerous clones of E.coli have gotten pathogenicity islands through horizontal gene transfer facilitates them to cause diarrheal diseases and urinary tract infections. There are six subdivisions of Diarrheal E.coli that can lead to sickness that ranges from mild diarrhea to acute systemic ailments (Lynch et al., 2009).
Shiga toxin-producing E. coli (STEC)
STEC is a zoonotic pathogen that colonizes mostly small ruminants and cattle. Even though products from cattle, mostly beef, is the most popularly identified sources of E.coli 0157 illnesses. Vegetables and fruits eaten raw are also a significant source. Three leaf attachment techniques have been observed in E. coli 0157 (Lan et al., 2009).
Enteroaggregative E. coli and enterotoxigenic E. coli
Enteroaggregative E.coli (EAEC) might be a significant causative agent of bacterial gastroenteritis within America (Nataro et al., 2006). Nevertheless, the EAEC reservoir is not known. Enterotoxigenic E. coli ( ETEC) is a significant causative agent of travelers' and infantile diarrhea and is responsible for causing severe watery diarrhea in piglets and calves (Lan et al., 2009).
Major Impact on Public Health and Economy
The safety of food has core implications on social behaviour, economy and human health. Outbreaks of food-borne diseases can result in considerable persons of people getting sick whereas attendant recalls coupled with publicity can minimize consumer confidence and reduce demand with considerable economic losses for every part of the supply chain. According to USDA Economic Research Service (ERS) estimates, annual productivity losses and medical costs due to food borne bacterial pathogens caused especially by salmonella infections ranged from $1.188 billion to more than $11. 588 billion on the basis of 1989 research of 1.92 million cases and ranging between 960-1,920 deaths (Berger et al., 2010).
Generally unsafe food is a great danger to worldwide health threats, putting the lives of everybody in danger. Young children, infants, the elderly, orphans and pregnant women as well as those having underlying sicknesses are especially susceptible (Berger et al., 2010). Around 220 million young children catch diarrheal ailments, with 96, 000 succumbing to death. Food that is not safe forms a vicious cycle of malnutrition and diarrhea putting the nutritional status of the most susceptible at risk. In instances where supply of food is not secure, people appear to move to less healthy diets and feed on more "unsafe foodstuffs" whereby microbiological, chemical as well as other hazards pose considerable risk (Berger et al., 2010).
The 2nd International Conference on Nutrition (ICN2) hosted by Rome in November of 2014, emphasized on the significance of food safety in attaining enhanced human nutrition via consumption of healthy and safe nutritious foodstuffs. Moreover, various governments should ascertain that they have made food safety a public health priority especially since they play an important role in drafting up policies and regulations. Moreover, such governments also establish and implement efficient food safety systems which make sure that suppliers and producers alongside the entire supply chain operate responsibly to ensure safest delivery of foods (Berger et al., 2010).
In addition, food can be contaminated at any given point between production and distribution, with the most important responsibility with producers of food. Because of such reasons, most producers as well as suppliers are dedicated to good practices meant for reduction of the contamination risk (Berger et al., 2010).
Suggestions/Recommendations for Preventing Occurrence Future Outbreaks
Normal techniques of preventing possible occurrence of outbreaks include post harvest decontamination processes. This can be done using natural household sanitizers such as vinegar and fresh lemon juice which have been confirmed to have some impact in Salmonella serovar Typhimurium reduction on spring onion and rocket leaves. Secondly treating commercial iceberg lettuce pre-inoculated using natural spoilage organisms by ozone, chlorine or the combination of the two minimizes the number of potential micro-organisms. Moreover combinations of chlorine-ozone increases the shell life of lettuce (Berger et al., 2010).
Microbial contamination has also been effectively reduced by ionizing radiation. Specifically, research focusing on leafy vegetables has demonstrated multiple log declines in Salmonella, Listeria monocytogenes, and E. coli O157:H7 whenever utilized on different greens comprising Romaine lettuce, spinach and iceberg lettuce (Niemira, 2008).
Conclusion
Making sure that the security of the present as well as future food supplies ranks amongst one of the key challenges facing many governments today. This is further fuelled by the requirement to feed a growing world population coupled with an insatiable demand for variety and freshness. Nonetheless, there exists a need of addressing issues linked to the supply of healthy and safe food. Governments world over have been encouraging consumption of fresh fruits and vegetables as an aspect of preventing disease and a healthy diet. in contrast, the fresh produce retail industry has designed value added items like bagged salad, that fulfill consumer requirements for variety and convenience (Berger et al., 2010).
This has been paralleled by a rising recognition of outbreaks of food borne diseases linked to the eating of fresh and ready-to-consume fruits, herbs and vegetables. Prevention endeavors must continue focusing on superior agricultural practices, enhanced traceability as well as excellent manufacturing processes (Berger et al., 2010). An enhanced understanding of microbiological, plant, environmental, processing, food and farm handling factors that interact with each other to establish whether contamination happens, or whether pathogens proliferate or survive will aid in the drafting of evidence-based procedures, technologies and policies aimed at enhancing fresh produce safety.





















Bibliography
BERGER, C., SODHA, S., SHAW, R. (2010). "Fresh fruit and vegetables as vehicles for the transmission of human pathogens." Environmental Microbiology (2010) 12(9), 2385-2397, doi:10.1111/j.1462-2920.2010.02297.x: p1-12.
CENTERS FOR DISEASE CONTROL AND PREVENTION. (2008). Outbreak of salmonella serotype Saintpaul infections associated with multiple raw produce items - United States, 2008. MMWR Morb Mortal Wkly Rep 57: 929-93
DONNAN EJ, FIELDING JE, GREGORY JE, LALOR K, ROWE S, GOLDSMITH P, ANTONIOU M, FULLERTON KE, KNOPE K, COPLAND JG, BOWDEN DS, TRACEY SL, HOGG GG, TAN A, ADAMOPOULOS J, GASTON J, VALLY H. (2011). A multistate outbreak of hepatitis A associated with semi-dried tomatoes in Australia, 2009. Clinical Infectious Diseases In press
FRIESEMA, I., SIGMUNDSDOTTIR, G., VAN DER ZWALUW, K., HEUVELINK, A., SCHIMMER, B., DE JAGER, C., ET AL. (2008). An international outbreak of Shiga toxin-producing Escherichia coli O157 infection due to lettuce, September-October 2007. Euro Surveill 13: pii=19065.
GERNER-SMIDT, P., HISE, K., KINCAID, J., HUNTER, S., ROLANDO, S., HYYTIA-TREES, E., ET AL. (2006). PulseNet USA: A five year update. Foodborne Pathog Dis 3: 9-19.
GIBSON, D.L., WHITE, A.P., SNYDER, S.D., MARTIN, SMUNNOCH SA, WARD K, SHERIDAN S, FITZSIMMONS GJ, SHADBOLT CT, PIISPANEN JP, WANG Q, WARD TJ, WORGAN TL, OXENFORD C, MUSTO JA, MCANULTY J, DURRHEIM D.N. (2009). A multi-state outbreak of Salmonella Saintpaul in Australia associated with cantaloupe consumption. Epidemiology and Infection 137(3):367-374
LAN, R., REEVES, P.R., AND OCTAVIA, S. (2009). Population structure, origins and evolution of major Salmonella enterica clones. Infect Genet Evol 9: 996-1005
LYNCH, M., TAUXE, R., & HEDBERG, C. (2009). "The growing burden of foodborne outbreaks due tocontaminated fresh produce: risks and opportunities." Cambridge University Press : p1-9.
MUNNOCH, S.A., WARD, K., SHERIDAN, S., FITZSIMMONS, G.J., SHADBOLT, C.T., PIISPANEN, J.P., et al. (2009). A multi-state outbreak of Salmonella Saintpaul in Australia associated with cantaloupe consumption. Epidemiol Infect 137: 367- 374.
NATARO, J.P., MAI, V., JOHNSON, J., BLACKWELDER, W.C., HEIMER, R., TIRRELL, S., ET AL. (2006). Diarrheagenic Escherichia coli infection in Baltimore, Maryland, and New Haven, Connecticut. Clin Infect Dis 43: 402-407
NIEMIRA, B.A. (2008). Irradiation compared with chlorination for elimination of Escherichia coli O157:H7 internalized in lettuce leaves: influence of lettuce variety. J Food Sci 73: M208-M213.
NYGARD, K., LASSEN, J., VOLD, L., ANDERSSON, Y., FISHER, I., LOFDAHL, S., ET AL. (2008). Outbreak of Salmonella Thompson infections linked to imported rucola lettuce. Foodborne Pathog Dis 5: 165-173.
PERSLEY, D., COOKE, T., & HOUSE, S. (2010). Diseases of vegetable crops in Australia. Collingwood, Vic, CSIRO Publishing.
SU, L.H., AND CHIU, C.H. (2007) Salmonella: clinical importance and evolution of nomenclature. Chang Gung Med J 30: 210-219
WESTRELL, T., CIAMPA, N., BOELAERT, F., HELWIGH, B., KORSGAARD, H., CHRÍEL, M., et al. (2009). Zoonotic infections in Europe in 2007: a summary of the EFSA-ECDC annual report. Euro Surveill 14: pii=19100.