Prevention of Infection From Food and Water
Christon J. Hurst
Gerald McDonnell
The subject of this chapter is microbial contaminants found either in food or in water, and the chapter primarily addresses microbial contaminants that infect humans. Before considering this topic, it is important for us to reflect on the broader issue of foodborne and waterborne disease. Many types of diseases have been associated with the consumption of food.1 Diseases also are associated with either ingestion or other types of exposure to water.2 These food-associated and water-associated diseases may be either acute or chronic. It is important to note that in the modern world today, many of the diseases associated with contaminants present in food or water are often caused by chemicals and are not specifically related to microbial contamination. Despite the disease hazards represented by chemical contaminants, the causative agents of foodborne and waterborne disease outbreaks continue to be frequently microbiological in nature. This is highlighted from the review of the top causes of death in the world today, which varies depending if you live in a high- or low-income country; in high-income countries, the major causes are ischemic heart disease, stroke, and dementia, whereas in low-income countries, communicable disease remains prevalent causes such as diarrheal diseases that are typically associated with food or water contamination.3 But even in high-income countries, outbreaks of infection and even death linked to such contaminants remain a frequent occurrence. The causes of such microbiological-associated diseases may represent either microbially produced toxins or infectious agents.
In general, foodborne disease outbreaks tend to be smaller but more numerous than waterborne disease outbreaks. Whereas it is true that in some cases, water is considered a food item because it is ingested, this chapter generally keeps with the more traditional custom of considering waterborne disease transmission as independent of food. There are notable connections between the subjects of foodborne and waterborne diseases in that food items can be contaminated by water. These connections between waterborne and foodborne diseases are noted within the chapter. The acquisition of infection from food items almost always is associated with ingestion of food. Usually, the only rare exceptions to this rule result when a microbial aerosol created during food handling is inhaled and causes a respiratory infection. Infections can be acquired from water by many different routes aside from ingestion, and these waterborne routes are described within the chapter. It is important to recognize that the associated microbial contaminants cause both individual and clusters of disease cases, even in the absence of recognized community-wide outbreaks. Both foodborne and waterborne infectious diseases represent substantial economic costs to society, not only in terms of medical treatment expenses but also the expense resulting from lost human productivity and even premature human death.
Most environmentally transmitted infections of humans seem to result from encountering pathogens that were contributed to the environment by other humans or animals. Therefore, we can prevent the transmission of these infections if we successfully prevent initial contamination of that food or water. This represents the aim of contamination-prevention programs such as crop and watershed protection, food and water disinfection (or commonly referred to as sanitation), the use of protective food packaging, and the use of closed containers or plumbing to transport potable water; however, additional environmentally associated illnesses result from microorganisms that are natural environmental inhabitants and many of these defy efforts at blocking the source of contamination. Included in the category of infectious agents that represent natural environmental inhabitants are numerous bacterial organisms such as Listeria monocytogenes, a soil organism that can cause meningitis if ingested; Legionella pneumophila, a water organism that can cause pneumonia if inhaled in a droplet aerosol; and Vibrio vulnificus, which can cause septicemia if it is present in bivalve mollusks that are ingested. Vibrio cholerae
represents a particularly interesting bacteria because it naturally resides in warm waters on the chitinous shell of crustaceans; we can acquire infections caused by these bacteria either by ingesting macrocrustaceans such as crabs as a food item or if we inadvertently ingest microcrustaceans contained in drinking water. The outcome of ingesting V cholerae by either of these processes leads to a diarrheal illness that can be transmitted by sewage; thus, infectious agents that might have been acquired from a food can lead to waterborne infection. Natural environmental microorganisms can cause other noninfectious illnesses associated with food items. Examples of bacterial species that cause such noninfectious illnesses are Clostridium botulinum, whose toxin causes nerve paralysis, and Clostridium perfringens, which, although normally associated with causing gas gangrene in deep wounds, will produce a toxin that can cause gastroenteritis when consumed.
represents a particularly interesting bacteria because it naturally resides in warm waters on the chitinous shell of crustaceans; we can acquire infections caused by these bacteria either by ingesting macrocrustaceans such as crabs as a food item or if we inadvertently ingest microcrustaceans contained in drinking water. The outcome of ingesting V cholerae by either of these processes leads to a diarrheal illness that can be transmitted by sewage; thus, infectious agents that might have been acquired from a food can lead to waterborne infection. Natural environmental microorganisms can cause other noninfectious illnesses associated with food items. Examples of bacterial species that cause such noninfectious illnesses are Clostridium botulinum, whose toxin causes nerve paralysis, and Clostridium perfringens, which, although normally associated with causing gas gangrene in deep wounds, will produce a toxin that can cause gastroenteritis when consumed.
A disease-causing microbe is less likely to be transmitted by an environmental route that exposes the organism to conditions under which it cannot easily survive; thus, infectious agents that are likely to have the greatest success at being transmitted in foods or water will logically have to be organisms that have evolved abilities to survive and even grow in food or water despite the natural or artificial (eg, preservative) methods employed to prepare them for consumption. We can use this general knowledge to our advantage by exposing the food or water to various treatment processes that impose conditions that will diminish the existing level of many types of pathogens and will help to prevent the growth of any infectious organisms that remain.
INTRODUCTION TO FOODBORNE INFECTIOUS DISEASESMicrobially contaminated foods represent a major source of human illness, and although these are often related to bacteria, they can include other pathogens including a large number of viral and protozoal diseases. Unlike chemical contaminants, some categories of microbial contaminants may be capable of replicating within the food, which can increase the disease hazard associated with the contaminated foods over the course of time. Indeed, thermal abuse, a term used to describe food that has been held at temperatures high enough to enable the growth of contaminating pathogenic bacteria or fungi, often has been associated with enteritis. Thermal abuse of foods usually is not implicated in protozoan- or viral-induced illnesses because protozoa that cause human enteric illnesses usually will not grow in stored foods and the human enteric viruses cannot grow in foods because viruses require viable animal host cells in which to replicate. The causative microbial contaminants found in food may have been acquired either from the environment or during the subsequent steps involved with food processing, packaging, and handling that occur prior to consumption.
Sources of Microbial Contaminants in Food
Microbial contamination of foods can occur within the environment before the food is harvested. Foods contaminated by water in this way include crustaceans and bivalve mollusks in which they live and vegetables contaminated by having been either irrigated with wastewater or fertilized with solids from wastewater. Foods also can be contaminated in the environment by processes that are not directly associated with contaminated water, with examples including Salmonella species (the bacterial agents associated with salmonellosis that may be acquired from ingesting eggs) and Campylobacter species (bacteria that cause campylobacteriosis, which may be acquired from both poultry and dairy products). Foods also can become contaminated with microorganisms at many different steps between the time of harvesting and eventual consumption. Some contamination is intentional, with certain bacteria and fungi deliberately added to food so that through their associated metabolic processes, these microorganisms will impart desired characteristics to the food. These characteristics include modifications of food coloration, texture, aroma, and taste. As an example, the gases released by respiration of yeasts cause bread to rise. Yeasts can ferment sugars to produce ethanol, which is a desired component of many beverages. Bacteria in the same beverages then can convert the ethanol and other compounds to acetic acid, thereby producing vinegar. Usually, it is the unintentional contamination of foods with microorganisms that is of public health concern. This contamination may result in spoilage of the food, production of microbial toxins, and infections of humans or animals that consume the food. It is the last of these categories of microorganisms—the unintentional contaminants—that will be addressed in the following text. Many of the individual foodborne pathogenic microorganisms are characteristically associated with specific types of foods (Table 37.1). These include not only many different categories of microorganisms (bacteria, protozoa, and viruses) but also some of the smaller types of microbial worms (metazoans such as cestodes and nematodes). These characteristic associations tend to represent contamination acquired either prior to harvesting or during processing operations performed before the food is marketed. Noncharacteristic associations between microorganisms and foods also have been noticed, and these tend to represent contamination that is acquired during the course of food handling after marketing. Some examples of these associations are Salmonella in orange juice,4 Giardia on raw sliced vegetables5 or in salads,6
Streptococcus in macaroni and cheese,7 and Calicivirus with freshly cut fruit.8
Streptococcus in macaroni and cheese,7 and Calicivirus with freshly cut fruit.8
TABLE 37.1 Examples of characteristic associations between foods and infectious diseasesa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Contamination Acquired From the Environment Prior to Harvesting
As suggested in the preceding discussion, microbial contamination can occur before harvesting, which also represents the first link in the chain of food production. As indicated, some of these microbial contaminants are hazardous because they infect consumers, but other microbes are primarily hazardous because of the toxins they produce. The predominant bacterial organisms associated with foodborne infectious disease seem to be Salmonella, Shigella, and Campylobacter species. Salmonella tends to be associated with both meat and eggs from poultry when those items are sold raw, and this is due to the fact that members of the genus Salmonella represent natural intestinal and cloacal microflora for avians. Salmonella also represent some risk for raw meat and eggs from terrestrial and freshwater reptiles because this genus of bacteria likewise colonizes the intestines and cloaca of those reptiles. In comparison, the bacterial contamination associated with raw eggs from marine turtles is of the genus Vibrio, which ecologically serves the marine environment in a role similar to that of Salmonella’s role in the terrestrial environments. Campylobacter seems to be associated with milk and likewise with poultry sold raw. The association of Vibrio with crustaceans and bivalve mollusks (such as mussels, clams, oysters, and scallops) represents natural microflora. Unfortunately, the natural colonization of the chitinous shells of crustaceans by Vibrio species can cause illness following ingestion if the crustaceans are not adequately cooked prior to ingestion. There is also some evidence that Vibrio species may be naturally present within the interior of the crustaceans. The association with Vibrio species as contaminants in bivalve mollusks presumably results from the mollusks having ingested these naturally present aquatic bacteria during the course of filter feeding.9 In fact, during the course of filter feeding, bivalve mollusks can become contaminated with any enteric pathogens present in the shellfish-growing waters, including bacteria, protozoans, and viruses.9 Salmonella, Pseudomonas, and Aeromonas species can be detected in bivalve mollusks, although it is not certain whether many of these contaminants are acquired prior to harvesting or during processing and handling. Disease problems with Escherichia, including the shiga-toxin strains of Escherichia coli O157:H7 strain, tend to be associated with ground beef sold raw.10 Interestingly, it is the strains of E coli associated with cattle that cause illness in humans, although at the same time, those humans presumably would find their intestines to be naturally colonized by nonpathogenic human-associated strains of E coli.
The predominant viruses associated with foodborne diseases are hepatitis A virus, which is the sole member of the Hepatovirus genus, and particularly Calicivirus, a genus most often represented by noroviruses or Norwalk and Norwalk-like viruses. These viruses are often associated with illnesses acquired from ingesting bivalve mollusks, where they are accumulated from water during the natural filter-feeding process used by the bivalve mollusks. Caliciviruses also may be associated with ice, an association that likely results from using virally contaminated water to produce the ice, and are commonly transmitted by the fecal-oral route (eg, known as a winter-vomiting bug). The Centers for Disease Control and Prevention estimates worldwide that noroviruses are responsible for 1 in 5 case of acute gastroenteritis and is the most common cause of diarrhea and vomiting associated with outbreaks of disease.11 Helminths, such as Taenia and Trichinella, usually are associated with meat from terrestrial mammals sold either raw or inadequately cooked and represent a disease-related infestation of the animals being slaughtered for food. Helminths of the genus Spirometra have a parallel association with fish. These bacterial, viral, and helminth contamination problems are characteristic associations.
The food-associated microorganisms listed earlier in this section cause illness by infecting the consumer. Some other microbial contaminants are notable for producing toxins that, when the food is ingested, cause diseases that represent intoxications.12 Dinoflagellate toxins can be accumulated by fish and shellfish prior to harvesting. Additional examples of environmentally acquired microbial toxins in foods are fungal toxins, such as aflatoxins, caused by the growth of fungi on plant materials either prior to harvesting or during storage.
Contamination Acquired During Processing and Production Prior to Marketing
Many foods are processed prior to marketing. In some cases, this can involve procedures as simple as washing and sorting, followed by packaging. Of course, processing can involve far more complex operations, including the addition of multiple ingredients from different sources and cooking. Each one of the steps involved, and each one of the ingredients added, represents an opportunity for microbial contamination. Contaminants can come from food contact surfaces, including processing equipment such as vats and plumbing. Biofilms are particular sources of microbial pathogens in these situations that are both actively growing in and associated with the biofilm; their resilience to cleaning and disinfection strategies is discussed further in chapter 67. Other sources of contamination are water used in washing operations, aerosols that can fall into the food as it is being processed and packaged, and the packaging material itself. Cross-contamination can occur between subsequently processed lots of raw ingredients. Cross-contamination also can occur between raw and cooked products if these come into contact with one another either directly or through the use of
common processing or packaging equipment. Assuring adequate disinfection at the processing step is particularly important in light of the fact that some microbial contaminants such as bacteria and fungi can grow in foods following packaging, and the distribution and marketing process for some foods may involve long periods during which that growth could occur. A few common examples of food items contaminated during processing are bacterial contaminations of meat, frozen fresh foods, and dairy products. Outbreaks of infection due to bacterial genus such as Listeria are frequently reported and linked with foodborne illness.13 Listeria are often associated with milk and other dairy products and is also associated with processed products containing red meat or poultry (such as sausages and luncheon meats) when these meat products are sold in a precooked, prepackaged form. Listeria are considered to be sourced from soil and animals and have been shown to be sourced from unsanitary factory production or food-handling practices. The presence of Shigella in food items presumably represents direct contact of the food with human feces or with the contaminated hands of workers, which can occur either prior to harvesting, during harvesting, or during processing prior to marketing.14
common processing or packaging equipment. Assuring adequate disinfection at the processing step is particularly important in light of the fact that some microbial contaminants such as bacteria and fungi can grow in foods following packaging, and the distribution and marketing process for some foods may involve long periods during which that growth could occur. A few common examples of food items contaminated during processing are bacterial contaminations of meat, frozen fresh foods, and dairy products. Outbreaks of infection due to bacterial genus such as Listeria are frequently reported and linked with foodborne illness.13 Listeria are often associated with milk and other dairy products and is also associated with processed products containing red meat or poultry (such as sausages and luncheon meats) when these meat products are sold in a precooked, prepackaged form. Listeria are considered to be sourced from soil and animals and have been shown to be sourced from unsanitary factory production or food-handling practices. The presence of Shigella in food items presumably represents direct contact of the food with human feces or with the contaminated hands of workers, which can occur either prior to harvesting, during harvesting, or during processing prior to marketing.14
Legal regulations were established to protect the quality of food products, perhaps the most important of which are regulations pertaining to the applications of risk assessment during the food preparation process, such as Hazard Analysis and Critical Control Point (HACCP) and associated controls such as disinfection (in food-associated applications often referred to as sanitation) practices. These help in controlling microbial quality not only of the basic material used in a food but also of additives as simple as potable water. Preventing microbial contamination requires close attention to sanitation practices. Good sanitation can result in food products that have a greater health safety level and may increase the shelf life of the product.15
Contamination Acquired During Handling and Preparation Following Marketing
Handlers involved in the preparation of food represent a major source of contaminants. Again, the largest factor involved is one of proper sanitation and aseptic practices. The infectious microbial contaminants associated with improper handling during food preparation tend to represent microorganisms that are present in the feces of infected persons and for which the transmission route involves ingestion of fecally contaminated materials.16 An example of bacterial disease caused by enteric microorganisms introduced during handling and preparation is with Salmonella typhi in a reconstituted beverage4 or with viruses such as noroviruses.17 These situations can be difficult to control due to the levels of microorganisms produced in different body excretions during illness (eg, 105-107 colony-forming units [CFUs] Salmonella per gram of feces or up to 106 CFU Staphylococcus per milliliter of saliva) as well as in asymptomatic individuals (eg, approximately 109 hepatitis A virions per gram feces in patients before symptoms of infection are seen).16 Handlers have even been reported to contaminate food through contact with infected wounds, resulting in outbreaks of diseases that normally are not considered to be enteric. An example of this route of bacterial contamination is an outbreak of streptococcus pharyngitis attributed to prepared macaroni and cheese.7
Examples of enteric protozoan contamination of foods that occurred during handling and preparation are Giardia in raw sliced vegetables,5,18 in a pasta salad,6 and from various grocery foods handled by asymptomatic carriers.19 Protozoan contamination of vegetables in one of those two outbreaks,5,18 and of the pasta salad, presumably represented cross-contamination contributed by water that had been used to prepare the food. The common-source giardiasis study18 represents a particularly interesting example of how microbial contaminants can be transferred from one type of contaminated material to another, creating a cycle of contamination. In that outbreak of giardiasis, it appears that raw food initially became contaminated by washing in tap water, after which the contaminated food was chopped on a cutting board. Other foods appear to have become contaminated when they were later prepared on that same cutting board, which was never adequately washed. Adequate washing of the cutting board to remove contaminating microorganisms physically, or disinfection of the cutting board, would have broken the cycle of contamination. Overall, water contamination is still the most prevalent source of protozoa associated with outbreaks, but food-borne contamination and outbreaks with Giardia, usually associated with food handlers, is estimated to be approximately 15% of cases.20 Examples of enteric viral contamination that may have originated during handling are represented by Calicivirus associated with freshly cut fruit8 and multiple enteric viruses (rotavirus, sapovirus, and norovirus) due to fecal contamination of salad.21
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
