Infectious dose
The infectious dose is the amount of agent that must be consumed to give rise to symptoms of foodborne illness, and varies according to the agent and the consumers age and overall health. Pathogens vary in minimum infectious dose; for example, Shigella sonnei has a low estimated minimum dose of < 500 colony-forming units (CFU) while Staphylococcus aureus has a relatively high estimate.In the case of Salmonella a relatively large inoculum of 1 million to 1 billion organisms is necessary to produce symptoms in healthy human volunteers, as Salmonellae are very sensitive to acid. An unusually high stomach pH level (low acidity) greatly reduces the number of bacteria required to cause symptoms by a factor of between 10 and 100. Gut microbiota unaccustomed to endemic organisms
Foodborne illness often occurs as travelers diarrhea in persons whose gut microbiota is unaccustomed to organisms endemic to the visited region. This effect of microbiologic naivete is compounded by any food safety lapses in the foods preparation. Epidemiology
Asymptomatic subclinical infection may help spread these diseases, particularly Staphylococcus aureus, Campylobacter, Salmonella, Shigella, Enterobacter, Vibrio cholerae, and Yersinia. For example, as of 1984 it was estimated that in the United States, 200,000 people were asymptomatic carriers of Salmonella. Infants
Globally, infants are a group that is especially vulnerable to foodborne disease. The World Health Organization has issued recommendations for the preparation, use and storage of prepared formulas. Breastfeeding remains the best preventive measure for protection from foodborne infections in infants.
Approximately 25% (90% CrI: 13%–42%) of the 15.9 million episodes of gastroenteritis that occur in Australia were estimated to be transmitted by contaminated food. This equates to an average of approximately one episode of foodborne gastroenteritis every five years per person. Data on the number of hospitalisations and deaths represent the occurrence of serious foodborne illness. Including gastroenteritis, non-gastroenteritis and sequelae, there were an estimated annual 31,920 (90% CrI: 29,500–35,500) hospitalisations due to foodborne illness and 86 (90% CrI: 70–105) deaths due to foodborne illness circa 2010. This study concludes that these rates are similar to recent estimates in the US and Canada.A main aim of this study was to compare if foodborne illness incidence had increased over time. In this study, similar methods of assessment were applied to data from circa 2000, which showed that the rate of foodborne gastroenteritis had not changed significantly over time. Two key estimates were the total number of gastroenteritis episodes each year, and the proportion considered foodborne. In circa 2010, it was estimated that 25% of all episodes of gastroenteritis were foodborne. By applying this proportion of episodes due to food to the incidence of gastroenteritis circa 2000, there were an estimated 4.3 million (90% CrI: 2.2–7.3 million) episodes of foodborne gastroenteritis circa 2000, although credible intervals overlap with 2010.