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Guide International Handbook of Foodborne Pathogens (Food Science and Technology)

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Foodborne Pathogens and Food Safety. Latiful Bari , Dike O. For Instructors Request Inspection Copy. Add to Wish List. Description Reviews Contents Series Subjects. Description Foodborne pathogens continue to cause major public health problems worldwide and have escalated to unprecedented levels in recent years.

Data are only available for confirmed cases, and it is generally accepted in the scientific community that the true incidence of foodborne disease is underreported. Of the estimated Because parasites Orlandi et al. H7 Buchanan and Doyle, , and viruses Cliver, have been addressed by previously published Scientific Status Summaries, these pathogens are not discussed here. Enterobacter sakazakii, an emerging pathogen of concern in infant formula, is a new inclusion in this revised Scientific Status Summary. Adapted from IFT The international impact of foodborne illness is difficult to estimate.

It is suspected that food or water is the vehicle for many of these illnesses WHO, Because food is biological in nature and is capable of supplying consumers with nutrients, it is equally capable of supporting the growth of contaminating microorganisms. Three types of bacterial foodborne diseases are recognized: Foodborne bacterial intoxication is caused by the ingestion of food containing preformed bacterial toxin, such as the toxins produced by Staphylococcus aureus and Clostridium botulinum, resulting from bacterial growth in the food. Foodborne infection, on the other hand, is caused by ingestion of food containing viable bacteria such as Salmonella or Listeria which then grow and establish themselves in the host, resulting in illness.

Foodborne toxicoinfections result when bacteria present in food, such as Clostridium perfringens, are ingested and subsequently produce a toxin in the host. The food industry implements a variety of effective control measures to limit potential hazards. This generally begins on the farm with the implementation of good agricultural practices. Some raw products, such as poultry, are subject to performance standards in spite of the fact that the consumer will presumably cook the product before consumption.

While all food manufacturers utilize control measures to ensure food safety, some food manufacturers are required to create and follow a Hazard Analysis and Critical Control Point HACCP plan. Critical control points identified through HACCP may include destruction or inactivation of the relevant bacteria or their spores through the use of heat treatments e. Additionally, extensive quality control procedures are maintained to ensure that these processes are effective. It is impossible, however, to create a risk-free food supply. While food manufacturers and distributors employ necessary control measures to ensure the safety of food until it reaches the consumer, all food handlers and consumers have the responsibility upon purchase of the food to maintain these control measures until consumption.

While outbreaks associated with a particular commercially processed food receive widespread public attention, a much greater number of individual cases of foodborne illness occurring in restaurants and in the home are not reported. Numerous surveys have highlighted inadequate home food storage and handling practices as major contributors to foodborne illness Altekruse et al.

For most of the pathogens discussed in this Scientific Status Summary Table 1 , illness can be avoided by heating and cooling foods to the appropriate temperatures, storing foods at the appropriate conditions for the recommended period of time, handwashing, and avoiding cross-contamination. Proper handling, cooking, and storage practices in foodservice operations and in the home can prevent the majority of foodborne illnesses. In the foodservice sector, education of the food preparer and server, with emphasis on good personal hygiene, is the best preventive measure.

Unfortunately, the majority of foodservice workers are young under 30 years of age , inexperienced, and stay on the job less than a year; thus, finding and educating these food handlers while they are actively working is difficult Marth, ; National Restaurant Association, Several studies and reviews have highlighted the contribution of changing demographics in the United States with the increased risk of foodborne illness Knabel, ; Zink, The increase in the elderly population and individuals with weakened immune systems underscores the need for rigorous food safety efforts, both on the part of the food manufacturer and the consumer.

Foodborne illnesses are more likely to be life-threatening for the immune compromised, the elderly, and individuals debilitated by underlying health problems such as cirrhosis, hepatitis, hemachromatosis, etc. Consumer education and increased regulatory control of foodservice establishments through inspection and strict enforcement of proper food handling practices probably have the greatest chances for success in controlling foodborne illness.

The need for continual education of consumers and all food handlers concerning the significant hazards associated with foodborne pathogenic microorganisms and proper food handling procedures is evident. Regulatory control over food handling in the home is not possible, but increased consumer education could have a beneficial effect. Salmonella is a generic name applied to a group of nearly 2, biochemically related serotypes responsible for foodborne illness.

The disease is grossly underreported because it is generally a self-limiting gastroenteritis which may be misdiagnosed as intestinal influenza by the patient or the physician.

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As a consequence, estimates of the true incidence of disease are based on assumptions derived from epidemiological evidence. Clearly, salmonellosis continues to be an important cause of foodborne disease worldwide. Two clinical manifestations caused by Salmonella are recognized: In both cases, the responsible microorganisms enter the body via the oral route. Enteric fever, commonly referred to as typhoid fever, is primarily caused by one species, Salmonella Typhi, but other salmonellae such as Salmonella Paratyphi are potentially capable of producing this syndrome.

The illness is commonly associated with foreign travel and affects an estimated people annually Mead et al. Although the route of entry of the pathogen into the body is primarily oral, the symptoms of enteric fever are generally not elicited through the intestinal tract. However, a short episode of vomiting and diarrhea sometimes occurs in the first day or two in typhoid fever.

The onset times vary considerably between typhoid and paratyphoid enteric fevers.

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Onset time for typhoid is usually 8—15 days, seldom as short as five days but sometimes as long as 30—35 days; while onset time for paratyphoid fever tends to be shorter, and may be so short as to suggest typical food poisoning Parker, The usual symptoms of both are headache, malaise, anorexia, and congestion of the mucous membranes, especially of the upper respiratory tract.

Bacteremia generally occurs in the first week of illness. Typically, common foodborne illness resulting from Salmonella infection is characterized by a self-limiting acute gastroenteritis. Contaminated food or water is the usual, but not the only, vehicle. The incubation period varies from six to 48 hr and generally falls within a range of 12—36 hr. Variation in the incubation time may be attributed to the size of the infecting dose, the virulence degree of pathogenicity of the microorganisms, the susceptibility of the host, and the physicochemical composition of the transmitting food.

Symptoms include diarrhea, abdominal cramps, vomiting, and fever, which generally last from one to seven days. However, the microorganisms may be excreted in the feces for many weeks after symptoms subside. Salmonellosis may be confused clinically with staphylococcal intoxication, but there are important distinctions. Salmonella has a longer incubation period than staphylococci usually 12—36 hr vs. And unlike Salmonella food poisoning, the acute symptoms of staphylococcal food poisoning normally disappear within 24 hours. Enlarge this Image Figure 1.

Salmonella Annual Summaries ; left axis: Newport, F Typhimurium; right axis: In some cases, gastroenteritis may be followed by extraintestinal invasion resulting in enteric fever, which is more likely to occur in the very young, the aged, and debilitated patients. Some Salmonella are host-adapted e. Although any Salmonella is a potential pathogen for humans, most foodborne salmonellosis is caused by non-host-adapted serotypes.

Much human salmonellosis is directly related to human association with animals, both wild and domestic. Foods of animal origin are vehicles for salmonellosis. In a review of Salmonella in meats and poultry, Silliker and Gabis introduced the problem as follows:. Contaminated red meat and poultry provide a nidus source of infection for Salmonella, which man nurtures through mishandling. Furthermore, inedible parts of the animal are processed to yield important components of livestock feeds. As a result of poor manufacturing practices postprocessing contamination , these rendered animal by-products become recontaminated with Salmonella, which, in turn, are carried into the feeds.

The consumption of these feeds by livestock, followed by animal-to-animal transmission, completes the Salmonella cycle. This is not to suggest, however, that contaminated feeds are the only source of Salmonella in livestock. Epidemiological evidence indicates that there is a direct link between the presence of Salmonella in meat and poultry and human salmonellosis.

Man induces salmonellosis through improper food handling practices and perpetuates salmonellosis through recontamination of rendered animal by-products, which are incorporated into livestock feeds. Historically, egg products dried, frozen or liquid eggs, with or without added ingredients, as defined in the Egg Products Inspection Act; U. Congress, were a significant source of human salmonellosis in the United States.

In , the U. Mandatory pasteurization of egg products was responsible for greatly reducing eggs as a major cause of salmonellosis, and consumer awareness of the need to refrigerate eggs also contributed in the decreased incidence of disease. However, since , the incidence of Salmonella Enteritidis has remained stable.

The microorganism is localized inside eggs, making thorough cooking imperative.

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This serotype was the second most commonly reported human serotype to the CDC in A portion of these illnesses occurred as a result of pooling raw shell eggs in institutional or foodservice settings. The potential for temperature abuse or long holding times, combined with the possibility of inadequate cooking, resulted in the recommendation that institutions use pasteurized egg products or pasteurized in-shell eggs instead of raw-shell eggs CDC, c. Consumption of raw milk may also cause human salmonellosis.

In one study, Salmonella was isolated in 6. Between —, 16 outbreaks of salmonellosis resulted from raw milk consumption CDC, a. Milk-borne salmonellosis was particularly prevalent in Scotland, where, prior to , the sale and consumption of raw milk was common Sharp, Milk outbreaks in England and Wales were primarily associated with raw milk. Pasteurization of milk destroys Salmonella and currently is the only effective means of control for milk. However, inadequate pasteurization or contact with raw milk after pasteurization can result in contaminated milk.

In one pasteurized milk outbreak in , there were more than 16, laboratory-confirmed cases of salmonellosis and several deaths Anonymous, Animal products are not the only sources of human salmonellosis. Produce can serve as a vehicle of Salmonella as well, becoming contaminated either on the farm or through cross-contamination with contaminated products. Consumption of produce contaminated with Salmonella has recently caused several outbreaks.

In , individuals in England and Wales acquired salmonellosis after eating lettuce, and although the lettuce appeared to come from one of three farms, investigators could not conclusively find the source of contamination Horby et al. Raw sprouts, particularly alfalfa and mung bean, have been involved in 15 salmonellosis outbreaks since Thomas et al.

Seeds may be contaminated, and the warm, moist conditions for sprouting allow growth of the pathogen. On-farm contamination of cantaloupes resulted in 24 cases of salmonellosis in Mohle-Boetani et al. Contamination of cantaloupes on one farm caused mulitstate outbreaks of salmonellosis each spring between and CDC, b. Since produce may be eaten raw, different control measures are necessary to prevent illness when the pathogen is introduced on the farm.

While Salmonella may survive in contaminated foods as a result of improper cooking, it is more common that cross-contamination of foods after cooking is the source of Salmonella.


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  • Foodservice workers or in-home food preparers may transfer salmonellae from raw products to cooked or other uncontaminated foods as a result of unsanitary preparation practices e. Salmonella can also be transferred from contaminated raw foods to equipment surfaces, such as knives, cutting boards, and counter tops, and then from equipment to previously uncontaminated foods.

    Once contamination occurs, the situation may be further complicated by improper storage of the product before serving e. Although responsible for fewer outbreaks, contamination of foods by infected workers cannot be ignored as a cause of foodborne salmonellosis. Some infected individuals may excrete Salmonella for weeks, months, and, occasionally, years with little or no evidence of disease.

    Improper hygiene practices by these individuals may lead to either contamination of foods or direct person-toperson contamination. Several approaches have been taken to reduce the carriage of Salmonella by animals. Vaccinination of laying chickens significantly reduced the percent of eggs positive for Salmonella Enteritidis Woodward et al. Other research has examined the effect of probiotics on the intestinal microflora of chickens. Successful reduction in the percent of the flock positive for Salmonella was achieved when the feed was supplemented with yeast Line et al.

    The performance standard percent positive was established by collecting the average baseline in the industry. Companies must use HACCP and other measures to ensure that the percent of their product that is positive for Salmonella falls below this baseline. The performance standard has been expanded to include steers, cows, broilers, hogs, and several related products FSIS, The most common method of eliminating Salmonella from food products is heat processing.

    Salmonella is heat sensitive, and ordinary pasteurization or cooking conditions are generally sufficient to kill it in high-moisture foods. As with other microorganisms, the heat resistance of Salmonella is markedly increased as water activity aw decreases. Minimum heat processes for pasteurization or cooking of most high-moisture products will eliminate Salmonella from these products. Occurrence of Salmonella in such processed products generally results from post-processing contamination. In some cases, dry products may be heat processed for the purpose of elimination of Salmonella.

    Ayres and Slosberg and Banwart and Ayres demonstrated the effectiveness of dry-heat treatment on reducing Salmonella in pan-dried egg white. This work led to the eventual requirement for dry-heat pasteurization of this product U. Similar treatments have been applied to gelatin, rendered animal by-products, nonfat dry milk, and chocolate.

    Other than heat, the major manufacturing factors responsible for elimination of Salmonella from food products are acidification and reduction of aw. Goepfert and Chung investigated the fate of Salmonella during sausage fermentation and concluded that the combination of acidity and sodium chloride was the principal reason for the demise of Salmonella during fermentation.

    Similarly, Smittle reviewed the literature on survival of Salmonella in mayonnaise and salad dressing and concluded that the principal factor responsible for the death of salmonellae in these products is acidity, but that a second important factor is reduction of aw as affected by moisture, NaCl, and sugar concentration. These same factors are responsible for control of Salmonella in a variety of fermented dairy, meat, and vegetable products.

    Salmonella may survive for extended periods in dehydrated foods. However, some death occurs during dehydrated storage, depending on the relative humidity or aw and storage atmosphere. The rate of death of Salmonella in food preserved by reduced aw is increased at higher aw levels, temperatures, and oxygen levels Genigeorgis and Riemann, In low-moisture products such as peanut butter and chocolate, Salmonella may remain for years, with little loss of viability.

    Moist, perishable products are generally distributed under refrigerated or frozen conditions. Although freezing and frozen storage can have some lethal effects on Salmonella, it is well recognized that Salmonella remain viable for long periods of time in frozen foods and that survival is enhanced as the storage temperature decreases Georgala and Hurst, The presence of Salmonella in certain types of produce seems to result from introduction of the pathogen on the farm. Contamination in these products, which are typically not heated before consumption, presents challenges to the food industry CDC, b; Thomas et al.

    For sprouts, chemical disinfection of the seed coat is not mandatory, but is recommended by the Food and Drug Administration FDA. A survey of sprout producers in California found that most alfalfa sprout growers followed FDA recommendations. Mung bean producers were less apt to follow the guidance Thomas et al. An outbreak involving 87 cases of Salmonella mbandaka was linked back to growers who did not disinfect seeds Gill et al.

    The recommended level of chlorine treatment, 20, ppm, still may not be sufficient to eliminate Salmonella, especially if they are localized inside the sprout tissue, as Gandhi et al. Therefore, compliance on the part of the grower, while worthwhile, does not guarantee a Salmonella- free product since chemical sanitizers may not be wholly sufficient to eliminate the presence of Salmonella in fruits and vegetables with natural openings and crevices Beuchat and Ryu, When purchasing items likely to be contaminated with Salmonella, such as chicken, there are steps the food handler can take to prevent salmonellosis from occurring in the home or food service environments.

    These general food safety practices include avoiding cross-contamination, thoroughly cooking foods, and storing foods at the right temperatures. Shigellosis, or bacillary dysentery, as it is commonly known, is caused by bacteria of the genus Shigella, which include S. The normal habitat for Shigella is the intestinal tract of humans and other primates. Although the primary mode of transmission appears to be personto- person by the fecal-oral route Feldman and Riley, , there have been some documented cases of foodborne shigellosis.

    The main source of Shigella involved in outbreaks is asymptomatic carriers or persons recovering from disease. Shigella may persist in the intestinal tract for months Bryan, Symptoms of shigellosis include diarrhea, abdominal pain, fever, and vomiting. The severity of the disease may vary from very mild to severe diarrhea with bloody stools, mucus secretia, and dehydration. Symptoms usually persist 3—14 days. Frequently, an asymptomatic carrier state may develop during convalescence, lasting from a few days to several months.

    Human-volunteer studies indicate that ingestion of as few as 10— microorganisms can induce illness Morris, The disease is caused by invasion of the intestinal mucosa. Enterotoxins, classically referred to as Shiga toxins, may be produced by S. Shiga toxins block mRNA transcription and induce apoptosis in endothelial cells Erwert et al. Secondary infections with Shigella occur frequently. Shigellosis can be a major problem in daycare centers, and control is difficult due to the low infectious dose, unpredictable acquisition of antimicrobial resistance, frequency of mild infections and carrier status, and the frequency with which young children are transferred from one daycare center to another CDC, The disease is disproportionately common among the urban poor, immigrants, Native Americans, daycare centers, and institutions Bryan, ; Morris, Extrapolated, this suggests almost 30, cases would be confirmed in the U.

    In the early s, S. The pattern of isolations suggests that prior to , direct fecal contamination of food and water supplies may have been the primary vector of disease.

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    As socioeconomic and environmental sanitation municipal sewage disposal, safe water supplies, and food hygiene have improved, the relative prevalence of S. The explanation for this phenomenon is not clear, but it may result from differences among the shigella in their ability to survive and grow outside their human and animal hosts.

    Shigella usually are considered to be relatively fragile; i. Like most other members of the family Enterobacteriaceae, they are readily killed by most heat treatments employed in the processing and preparation of foods, and do not survive well at pH below 4. However, studies on the survival of shigella suggest that under certain selected conditions, they can survive for extended periods in foods Bryan, These laboratory data suggest that shigella may survive for extended periods in foods and may grow under selected conditions. However, in practice, Shigella is rarely isolated from processed products.


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    Manufacturers do not routinely test their products, raw materials, or processing environments for Shigella, and there is no evidence to suggest that routine testing is warranted. Most outbreaks result from contamination of raw or previously cooked foods during preparation in the home or in foodservice establishments. Generally, the source of contamination can be traced to a carrier whose personal hygiene is poor Bryan, In underdeveloped countries, harvesting of seafood from fecally contaminated waters and use of unsanitary water in food preparation may be sources of disease.

    Shigellosis is a significant cause of foodborne illness in both developed and developing countries. Food microbiologists should be aware that Shigella species can cause a rather severe form of foodborne illness Smith, and that relatively low numbers of the microorganisms can cause disease. Products suspected of foodborne illness should be analyzed for Shigella.

    Further studies are needed to determine the roles of the various toxins and virulence factors in the disease process. The epidemiology of shigellosis should be reevaluated, with particular emphasis on the environmental factors associated with the increasing incidence of S. The waning incidence of S. Thus, prevention and control of shigellosis requires either that infected humans not be permitted to handle foods or that they practice good personal hygiene such that, even if infected, the food does not become contaminated.

    Certainly, exclusion of infected individuals from food handling is desirable. However, routine testing of food workers for Shigella is neither practical nor necessary. The principles necessary for control of Shigella at the preparation and service level are the same as those necessary for control of other more widely recognized pathogens such as Salmonella and Campylobacter. The increasing awareness of consumers and employees of foodservice establishments of the potential for foodborne diseases should do much to reduce the incidence of shigellosis in the developed countries.

    In the developing countries, control of shigellosis, as always, will depend on improved hygiene and waste-handling practices. Enlarge this Image Figure 2. Relative contribution of species of Shigella causing foodborne illness; g S. Originally considered a pathogen principally of veterinary significance, Campylobacter jejuni formerly known as Vibrio fetus was known to cause abortion in sheep. Other enteric campylobacters that may be transmitted through food include C.

    Following the development of procedures for detecting campylobacters in stool specimens, C. Common symptoms of Campylobacter enteritis include profuse watery or sticky diarrhea sometimes containing blood , abdominal cramps, headaches, muscle pain, and nausea. The mortality rate is low 0. Human volunteer and retrospective studies of food-associated outbreaks of Campylobacter enteritis revealed that ingesting relatively small numbers only a few hundred cells of C.

    Symptoms manifest after an incubation period of two to five days, and generally last 7—10 days. Campylobacters are harmless inhabitants of the gastrointestinal tract of a variety of wild and domestic animals. For this reason, the microorganism is often associated with unprocessed foods of animal origin. In a outbreak, raw lettuce served as the vehicle for Campylobacter infections, presumably after contact with raw chicken CDC, Other foods implicated as vehicles of outbreaks include raw milk, raw beef, clams, and cake likely contaminated by a C.

    Incompletely pasteurized milk was responsible for an outbreak of Camplyobacter enteritis affecting people in the United Kingdom Fahey, Estimates from studies in England and Wales revealed that approximately 25, cases of foodborne illness were caused by C. Outbreaks of Camplylobacter enteritis are generally small; however, untreated surface water used in municipal water supplies has been responsible for large outbreaks involving thousands of individuals.

    The principal route by which C. Raw meats and poultry become contaminated during processing when intestinal contents contact meat surfaces. Raw milk may be contaminated by contact with bovine feces or possibly by a mastitic infection of the bovine udder. Fresh produce can be contaminated by fecal-laden irrigation water, infected harvesters with poor hygienic practices, or tainted processing water.

    Although eggs have rarely been linked to outbreaks of Campylobacter enteritis, C. However, the microorganism is often associated with and transmitted by raw, refrigerated foods of animal origin. Pasteurization will eliminate viable campylobacters in milk. Use of potable irrigation and processing water and safe food handling practices by harvesters are important to the safety of produce. Freezing food will substantially reduce the initial Campylobacter population; however, a small number of survivors may remain viable for many months Moorhead and Dykes, Yersinia enterocolitica is not a frequent cause of human infection in the United States; illness is more common in Northern Europe, Scandinavia, and Japan.

    Although CDC estimates that there are 17, cases of yersiniosis, the infection caused by Y. When the microorganism is involved in illness, which typically manifests 24—48 hr after ingestion, the symptoms can be quite severe; but fatalities are rare. The infective dose is unknown. Yersiniosis occurs most commonly in the form of gastroenteritis.

    Children are most severely affected with symptoms of intense abdominal pain often mimicking appendicitis , diarrhea, fever, and vomiting. Symptoms of pseudoappendicitis have resulted in many unnecessary appendectomies in children. Fatality from gastroenteritis is rare, and recovery is generally complete within one or two days. Other syndromes may include mesenteric lymphadenitis, terminal ileitis, erythema nodosum, septicemia, and meningitis. However, most animal isolates, with the exception of swine isolates, are not human pathogens.

    Swine is an important and the principal reservoir for virulent strains of Y. A study in Japan revealed that rats in slaughterhouse areas may also be carriers of virulent types of Yersinia Zen-Yoji et al. Not surprisingly, because swine are the primary reservoir of virulent types of Y. The product, known as chitterlings, is traditionally eaten during the winter holidays, generally by African Americans, and the incidence of yersiniosis increases in December for the consuming population.

    Infants and children are most often affected, largely because of caretakers who do not properly wash their hands between preparing chitterlings and feeding young children, or practice adequate kitchen hygiene Jones et al. For epidemiological purposes, these cases are not reported as foodborne illness, since the food is not ingested, but clearly the porcine intestines served as the source of the pathogen.

    A study of bulk tank milk revealed that 6. Further testing determined that all strains were virulent Jayarao and Henning, Chocolate milk, pasteurized milk, and tofu packed in unchlorinated spring water have all been vehicles of outbreaks of yersiniosis Ackers et al. The precise mode of transmission was not determined, but in each situation there was thought to be a lack of sanitary practice or deficiencies in good manufacturing practices. Circumstantial evidence suggests that porcine waste may have been the original source of Y.

    The infrequent presence of pathogenic strains in foods may explain why there are relatively few reported food-associated outbreaks of yersiniosis. The microorganism is one of a few foodborne pathogens that can grow at refrigeration temperatures. Hence, refrigeration, which traditionally has been an important means of controlling the growth of foodborne pathogens, is not an effective method for controlling Yersinia. However, since Yersinia will grow at refrigeration temperatures, cold storage can be a means of selectively promoting growth of the microorganism in foods.

    Therefore, it is important to eliminate the microorganism from foods especially pork, milk, and foods that may have direct or indirect contact with porcine waste by pasteurization or cooking. Care should be taken to avoid cross-contamination of processed, RTE foods with pork and porcine wastes, as well as animal and human fecal contamination.

    Prior to the s, listeriosis, the disease caused predominantly by Listeria monocytogenes, was primarily of veterinary concern, where it was associated with abortions and encephalitis in sheep and cattle. Interestingly, evidence indicates that veterinary listeriosis was frequently foodborne. As a result of its wide distribution in the environment, its ability to survive for long periods of time under adverse conditions, and its ability to grow at temperatures as low as —0.

    Immunocompromised humans are highly susceptible to virulent Listeria. Only the hemolytic species of Listeria L. Of these, only L. Listeriosis is a very serious and often fatal infection primarily affecting the elderly and perinates. However, gastrointestinal illness has recently been recognized as a possible manifestation of ingestion of Listeria.

    Unlike the more severe form of listeriosis, gastrointestinal illness, which generally results more than 12 hr after ingestion, primarily affects seemingly healthy adults. In some instances, this type of illness is associated with the consumption of large doses of L. In humans, ingestion of as few as 1, cells of the bacteria, which then invade macrophages, may be marked by a flu-like illness malaise, diarrhea, and mild fever. This enteric phase, however, may be without symptoms, or so mild as to go unnoticed. A carrier state may develop.

    Following invasion of macrophages, virulent strains of Listeria may then multiply, resulting in disruption of these cells and septicemia. The stage of pregnancy upon exposure of the fetus to the microorganism determines the outcome for the fetus abortion, stillbirth, or neonatal sepsis. Fever is a common symptom, and other complaints may vary from nonspecific fatigue and malaise to enteric symptoms.

    Forms of listeriosis involving the central nervous system include meningitis, encephalitis, and abscesses. Localized forms of listeriosis, which are rare, include endocarditis, endophthalmitis, and osteomyelitis, with the involvement of other sites such as skin, spleen, gall bladder, and lymph nodes.

    All forms of listeriosis are more likely to accompany immunocompromised states, whether natural as in pregnancy, or in the elderly or induced as a result of medical treatment such as with corticosteroids. Individuals using antacids or cimetidine may also be more susceptible to infection, because of changes in stomach acidity.

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    Biological oxidation during wastewater treatment favors the growth of Listeria in sewage. Sludge provides a favorable environment for survival and growth of L. This makes the use of sewage plant effluent or waters receiving sewage plant effluent for irrigation of edible crops dangerous. The use of sludge for fertilization of edible crops is equally hazardous. Environments with pH values outside that range are unfavorable for survival.

    The microorganism has readily survived the pH 5 environments of cottage cheese and ripening Cheddar cheese, and was detectable in the latter product pH 5. Listeria is salt tolerant, growing to levels of visible turbidity in the laboratory media Tryptic Soy Broth pH 5. Listeria is reported to survive for three months in dry fodder and more than six months in dry straw.

    Dry feces have been reported to maintain viability of the microorganism for more than two years Gray, , and survival in soil for up to days has been recorded. Listeria is relatively resistant to drying, as demonstrated on glass beads and tile surfaces. The first reported outbreak of foodborne listeriosis occurred between March and September Coleslaw was implicated as the cause of 34 cases of perinatal listeriosis and seven cases of adult listeriosis in the Maritime Province of Nova Scotia.

    Perinatal cases were characterized by acute febrile illness in pregnant women, followed by spontaneous abortion five cases , stillbirth four cases , live birth of a seriously ill premature or term infant 23 cases , or live birth of a well infant two cases. The outbreak strain was isolated from two unopened packages of coleslaw from the plant but was not cultured from the manufacturing plant environment.

    The incriminated coleslaw was traced to a farm where the cabbage was grown in fields fertilized with sheep manure.

    Two of the sheep on the farm had previously died from listeriosis Schlech et al. Hot dogs and deli meats contaminated with L. In , 63 cases of listeriosis, of which three were perinatal, resulted from the consumption of sliced deli meat in eight Northeastern states. This type of food product was also responsible for an outbreak in affecting 29 people in 10 states CDC, a. The soft cheeses are now infamous for their susceptibility to contamination with L. Not only is the manufacturing process open to contamination, but the cheese can serve as a growth environment where L.

    Mexican-style cheese made with raw milk was implicated in two separate outbreaks, one in causing illnesses, and one in — resulting in 12 cases. The mortality rate was While association of listeriosis with raw milk consumption is not rare, it is infrequent and sporadic. The results of surveys of raw milk for L. The presence of L. The risk assessment prepared jointly by the agencies estimated the relative risk of listeriosis in 23 categories of RTE foods.

    In terms of risk per serving, deli meats ranked as having the highest risk. Because of the link between dairy foods, particularly milk, and L. Two studies by Bunning et al. The control of Listeria in food products begins at the lowest level in the processing chain—at the raw product source. The growing environment should be kept free of the opportunity for potential contamination.

    Waters suspected of contamination by Listeria, sewage plant effluent, and sewage sludges should not be used to produce crops that will be eaten without cooking or that will become an ingredient of a product that will be eaten raw. Containers, cartons, boxes, tankers, trucks, or rail cars used to transport the product to the process plant should be frequently cleaned. At the plant, the raw product itself becomes a source of contamination for the environment. Personnel, too, must have their movements within the plant restricted depending on their exposure to potential contamination.

    There should be no cross-connections between raw and finished product, whether these cross-connections be humans, equipment, water, air, or the piping arrangement within the plant. If a personnel practice or movement within the plant provides contamination potential, it should be eliminated or modified.