The media and the public generally focus first on the actual pathogen when a foodborne illness occurs, eventually turning their focus to the source of the illness. Often, an infected person causes the outbreak directly—or even indirectly—through a series of improper actions or inactions. Humans can be considered the parameter of these illnesses.
The word “parameter” has many definitions. In math and statistics, it is a constant or variable term or a set of independent variables or a variable entering into the mathematical form. More generally, a parameter is a characteristic or a factor. Humans are both a constant and a variable factor in the epidemiology of foodborne illnesses.
The issue of food safety can be considered from a microbial ecological perspective, with foodborne disease falling into two key niches or source environments that people provide: soil and water, and non-fecal body fluids.
This discussion will exclude fecal and dermal, because these two sources of pathogenic contamination can be lengthy topics. And much has been described and discussed regarding good manufacturing practices (GMPs) pertaining to personal hygiene, specifically hand washing and sanitizing, which are primary control measures for fecal and dermal transmission routes. In every instance, however, proper control and prevention measures ultimately deal with the source vectors of the pathogen.
Each of these sources can and do involve multiple transmission routes. For example, in some cases, a single “lone wolf” causes the entire outbreak or contaminates other food workers who create the epidemiological thread. In other outbreaks, the food worker provides a low level of contamination through one of the four sources, and environmental conditions permit its proliferation.
These have been organized into categories of outbreaks based on the infective behavior or pattern of human-mediated contamination resulting in foodborne illnesses, as well as subsets of categories, because of the variable and dynamic nature of food handling and processing systems.1
These sources have both unique and overlapping microbial pathogens of concern, another reason epidemiological investigations are not always crystal clear about the source. Does the implicated Staphylococcus aureus or Salmonella serotype come from a person, an animal, or a secondary source? Clearly, specific viral and bacterial pathogens cause the majority of human-mediated foodborne disease.
Viruses are implicated in roughly 60% of all human-mediated foodborne outbreaks. The noroviruses and hepatitis A are involved in more than 30% and 10%, respectively, of all the viral-associated outbreaks. Approximately 35% of all outbreaks involve these pathogens: Salmonella spp., Staphylococcus aureus, Shigella spp., groups A and G Streptococcus, Vibrio cholerae, Campylobacter jejuni, and E. coli 0157:H7.2 Noroviruses have been found in every key food category or group, as have Salmonella, S. aureus, and Streptococcus spp.2,3
Soil and Waterborne
Both the food industry, with its good agricultural practices, and the food processing, food service, and retail industries have measures in place to control inadvertent transfer of soil-borne and other environmental carriers. Unfortunately, lack of enforcement or control enables pathogens to contaminate products and cause illness in consumers.
Clothing, jewelry, and street shoes are notorious carriers of fomites, the objects or materials that serve as carriers from one person to another or to a food product. In many food processing plants, fomite control through prohibition of street clothes and shoes is one of the most successful GMP tools available.
Street shoes will bring in copious amounts of fomites containing Listeria species and other non-spore-forming gram-positive bacteria, including L. monocytogenes, Streptococcus, and Staphylococcus.
In some food plant operations, however, smocks are required, but street shoes can be worn with no plastic or rubber covers. This lack of control can and does increase in the service and retail segments of the food chain, resulting in a flood of fomites that can potentially spread food pathogens of all types. Key vectors of fomites include:
- Shoes, street clothes, and rings. Street shoes will bring in copious amounts of fomites containing Listeria species and other non-spore-forming gram-positive bacteria, including L. monocytogenes, Streptococcus, and Staphylococcus. If the soil is moist or wet, enteric microbes like E. coli 0157:H7, Salmonella, and even Shigella can be transferred into a food handling/processing environment. If the soil fomites are from more arid sources, the fungal and bacterial spore-forming pathogens, including Clostridium botulinum and Bacillus cereus, will ride in on them.
- Carpets, anti-fatigue mats, or a white rag used to improperly wipe a food service counter or table can transmit pathogens. All microbial carriers usually have a nice layer of organic material that shields the pathogenic microbes from environmental stresses while also providing nutrients. Several studies have established that non-spore-forming microbial pathogens like Staphylococcus and Salmonella species can survive more than 24 hours on dried surfaces.4 Other enteric non-spore-forming pathogens like Enterococcus faecium can survive up to seven days.5