320 ◾ Fundamental Food Microbiology
Estimated Foodborne Illnesses
For a long time, there was a difference in opinion regarding the actual number of foodborne illness
cases versus the number of cases reported annually in the United States. The average number of
about 20,000 cases reported annually was thought to be too low. A realistic figure was estimated
to be anywhere in the range of 5–25 million and there were individuals who thought it to be as
high as 80 million.
Recently, a group of researchers at CDC published a report on the estimated number of cases
of foodborne illnesses from both known as well as unknown causes. 1 They compiled and analyzed the information gathered by several surveillance systems (e.g., FoodNet) and other relevant sources. According to this report, the total number of foodborne illnesses from known and
unknown causes was estimated to be 48 million annually with 128,000 hospitalizations and 3000
deaths in the United States. Among these, the known pathogens account for an estimated 9.4
million illnesses, 56,000 hospitalizations, and 1351 deaths (Table 24.3). Of these, nontyphoidal
Salmonella was responsible for 28% of these deaths, followed by Toxoplasma gondii (24%), Listeria
monocytogenes (19%), and norovirus (11%).
They indicated that via different surveillance programs, an accurate number of illnesses associated with outbreaks caused by some pathogens were available. However, sporadic illnesses, especially for pathogens like Bac. cereus, Clo. perfringens, and Sta. aureus are not accurately available
through such programs. For those pathogens, the outbreak-related cases were multiplied by 10 to
obtain the total number of illnesses through sporadic as well as outbreak incidences. The basis of
using this multiplier was from data where both sporadic and outbreak illnesses were available, such
as for Salmonella and Shigella.
Some other important aspects mentioned in this report are that even with the current surveillance programs, the foodborne illnesses are underreported (Figure 24.1); many pathogens
that are transmitted through food can also be transmitted through water and person to person,
thus obscuring the role of foodborne transmission. Also, some of the current foodborne illnesses
are caused by pathogens that have not yet been identified or caused by emerging pathogens (see
Chapter 29). 1
Conclusion
The material presented in this chapter shows that foodborne diseases, either sporadic or outbreaks,
can be caused by different pathogenic microorganisms, some of which are more predominant than
others. The different parameters associated with the predominant factors (pathogenic bacteria and
viruses) were also described. Finally, the sequence of events necessary for a foodborne disease to
occur was discussed. This information will be helpful in understanding the material presented in
the next chapters.
QUESTIONS
1. List the factors associated with a foodborne disease outbreak.
2. Define or explain an outbreak, a reported case, and a confirmed outbreak.
3. Survey 25 of your friends and relatives about the number of individuals had, at least once, a
digestive disorder in the last 2 years. From this, calculate approximately how many people
can be affected with foodborne disease in the United States per year. Is it close to 20,000? 5
million? 25 million? or 80 million?
Estimated Foodborne Illnesses
For a long time, there was a difference in opinion regarding the actual number of foodborne illness
cases versus the number of cases reported annually in the United States. The average number of
about 20,000 cases reported annually was thought to be too low. A realistic figure was estimated
to be anywhere in the range of 5–25 million and there were individuals who thought it to be as
high as 80 million.
Recently, a group of researchers at CDC published a report on the estimated number of cases
of foodborne illnesses from both known as well as unknown causes. 1 They compiled and analyzed the information gathered by several surveillance systems (e.g., FoodNet) and other relevant sources. According to this report, the total number of foodborne illnesses from known and
unknown causes was estimated to be 48 million annually with 128,000 hospitalizations and 3000
deaths in the United States. Among these, the known pathogens account for an estimated 9.4
million illnesses, 56,000 hospitalizations, and 1351 deaths (Table 24.3). Of these, nontyphoidal
Salmonella was responsible for 28% of these deaths, followed by Toxoplasma gondii (24%), Listeria
monocytogenes (19%), and norovirus (11%).
They indicated that via different surveillance programs, an accurate number of illnesses associated with outbreaks caused by some pathogens were available. However, sporadic illnesses, especially for pathogens like Bac. cereus, Clo. perfringens, and Sta. aureus are not accurately available
through such programs. For those pathogens, the outbreak-related cases were multiplied by 10 to
obtain the total number of illnesses through sporadic as well as outbreak incidences. The basis of
using this multiplier was from data where both sporadic and outbreak illnesses were available, such
as for Salmonella and Shigella.
Some other important aspects mentioned in this report are that even with the current surveillance programs, the foodborne illnesses are underreported (Figure 24.1); many pathogens
that are transmitted through food can also be transmitted through water and person to person,
thus obscuring the role of foodborne transmission. Also, some of the current foodborne illnesses
are caused by pathogens that have not yet been identified or caused by emerging pathogens (see
Chapter 29). 1
Conclusion
The material presented in this chapter shows that foodborne diseases, either sporadic or outbreaks,
can be caused by different pathogenic microorganisms, some of which are more predominant than
others. The different parameters associated with the predominant factors (pathogenic bacteria and
viruses) were also described. Finally, the sequence of events necessary for a foodborne disease to
occur was discussed. This information will be helpful in understanding the material presented in
the next chapters.
QUESTIONS
1. List the factors associated with a foodborne disease outbreak.
2. Define or explain an outbreak, a reported case, and a confirmed outbreak.
3. Survey 25 of your friends and relatives about the number of individuals had, at least once, a
digestive disorder in the last 2 years. From this, calculate approximately how many people
can be affected with foodborne disease in the United States per year. Is it close to 20,000? 5
million? 25 million? or 80 million?