Routes of Transmission in the Food Chain

More than 250 different foodborne diseases have been described to date, annually affecting about one-third of the world's population. The incidence of foodborne diseases has been underreported and underestimated, and the asymptomatic presentation of some of the illnesses, worldwide heterogeneities in reporting, and the alternative transmission routes of certain pathogens are among the factors that contribute to this. Globalization, centralization of the food supply, transportation of food products progressively farther from their places of origin, and the multitude of steps where contamination may occur have made it increasingly challenging to investigate foodborne and waterborne outbreaks. Certain foodborne pathogens may be transmitted directly from animals to humans, while others are transmitted through vectors, such as insects, or through food handlers, contaminated food products or food-processing surfaces, or transfer from sponges, cloths, or utensils. Additionally, the airborne route may contribute to the transmission of certain foodborne pathogens. Complicating epidemiological investigations, multiple transmission routes have been described for some foodborne pathogens. Two types of transmission barriers, primary and secondary, have been described for foodborne pathogens, each of them providing opportunities for preventing and controlling outbreaks. Primary barriers, the most effective sites of prophylactic intervention, prevent pathogen entry into the environment, while secondary barriers prevent the multiplication and dissemination of pathogens that have already entered the environment. Understanding pathogen dynamics, monitoring transmission, and implementing preventive measures are complicated by the phenomenon of superspreading, which refers to the concept that, at the level of populations, a minority of hosts is responsible for the majority of transmission events.