Infectious dose

The infectious dose is the amount of agent that must be consumed to give rise to symptoms of food borne illness, and varies according to the agent and the consumer's age and overall health. In the case of Salmonella a relatively large inoculums 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.

Outbreaks

The vast majority of reported cases of food borne illness occur as individual or sporadic cases. The origin of most sporadic cases is undetermined. In the United States, where people eat outside their home frequently, most outbreaks (58%) originate from commercial food facilities. An outbreak is defined as occurring when two or more people experience similar illness after consuming food from a common source.

Often, a combination of events contributes to an outbreak, for example, food might be left at room temperature for many hours, allowing bacteria to multiply which is compounded by inadequate cooking which results in a failure to kill the dangerously elevated bacterial levels.

Outbreaks are usually identified when those affected know each other. However, more and more, outbreaks are identified by public health staff from unexpected increases in laboratory results for certain strains of bacteria.

Society and culture

Many outbreaks of food borne diseases that were once contained within a small community may now take place on global dimensions. Food safety authorities all over the world have acknowledged that ensuring food safety must not only be tackled at the national level but also through closer linkages among food safety authorities at the international level. This is important for exchanging routine information on food safety issues and to have rapid access to information in case of food safety emergencies."

It is difficult to estimate the global incidence of food borne disease, but it has been reported that in the year 2000 about 2.1 million people died from diarrheal diseases. Many of these cases have been attributed to contamination of food and drinking water. Additionally, diarrhea is a major cause of malnutrition in infants and young children.

Even in industrialized countries, up to 30% of the population of people has been reported to suffer from food borne diseases every year. In the U.S, around 76 million cases of food borne diseases, which resulted in 325,000 hospitalizations and 5,000 deaths, are estimated to occur each year. Developing countries in particular are worst affected by food borne illnesses due to the presence of a wide range of diseases, including those caused by parasites. Food borne illnesses can and did inflict serious and extensive harm on society. In 1994, an outbreak of salmonellosis due to contaminated ice cream occurred in the USA, affecting an estimated 224,000 persons. In 1988, an outbreak of hepatitis A, resulting from the consumption of contaminated clams, affected some 300,000 individuals in China.

Food contamination creates an enormous social and economic strain on societies. In the U.S., diseases caused by the major pathogens alone are estimated to cost up to US $35 billion annually (1997) in medical costs and lost productivity.