Foodborne Gastroenteritis Caused by Salmonella and Shigella
625
In dry foods, S. Montevideo was found to be more resistant than S. Heidelberg when inoculated
into dry milk, cocoa powder, poultry feed, meat, and bone meal.
29 Survival was greater at a w 0.43 and
0.52 than at a w 0.75.
The Salmonella Food-Poisoning Syndrome
This syndrome is caused by the ingestion of foods that contain significant numbers of non-hostspecific species or serotypes of the genus Salmonella. From the time of ingestion of food, symptoms
usually develop in 12–14 hours, although shorter and longer times have been reported. The symptoms
consist of nausea, vomiting, abdominal pain (not as severe as with staphylococcal food poisoning),
headache, chills, and diarrhea. These symptoms are usually accompanied by prostration, muscular
weakness, faintness, moderate fever, restlessness, and drowsiness. Symptoms usually persist for 2–3
days. The average mortality rate is 4.1%, varying from 5.8% during the first year of life, to 2% between
the first and 50th year, and 15% in persons over 50 years. Among the different species of Salmonella,S.
Choleraesuis has been reported to produce the highest mortality rate—21% (see Chapter 22).
Although these organisms generally disappear rapidly from the intestinal tract, up to 5% of patients
may become carriers of the organisms upon recovery from this disease.
Numbers of cells on the order of 10
7 –10
9 /g are generally necessary for salmonellosis. That outbreaks may occur in which relatively low numbers of cells are found has been noted.
18 From three
outbreaks, the numbers of cells found were as low as 100/100 g (S. Eastbourne in chocolate) to 15,000/g
(S. Cubana in a carmine dye solution). In general, minimum numbers for gastroenteritis range between
10
5 and 10
6 /g for S. Bareilly and S. Newport to 10
9 –10
10 for S. Pullorum.
8
Salmonella Virulence Properties
Although an enterotoxin and a cytotoxin have been identified in pathogenic salmonellae, they seem
to play only a minimal (if any) role in the gastroenteritis syndrome. The virulence mechanisms of the
salmonellae continue to be unravelled, and summaries of what is known are presented in Chapter 22
along with other Gram-negative foodborne pathogens. A synopsis of the early history of salmonellae
pathogenesis can be found in the previous edition of this text.
Incidence and Vehicle Foods
The precise incidence of salmonellae food poisoning in the United States is not known. However, the two largest recorded outbreaks of salmonellosis occurred under rather unusual circumstances. The largest occurred in 1994 and it involved more than 224,000 persons.
23 The vehicle
food was ice cream produced from milk that was transported in tanker trucks that had previously hauled liquid eggs. The serovar was S. Enteritidis, and cases were seen in at least 41 U.S.
states. The next largest outbreak occurred in 1985 and involved close to 200,000 persons.
48 (See
Fig. 26–1 and Fig. 26–2.) The vehicle was 2% milk produced by a single dairy plant in Illinois,
and S. Typhimurium was the etiological agent (see Figures 26–1 and 26–2). The third largest outbreak occurred in 1974 on the Navajo Indian Reservation, when 3,400 persons became ill.
26 The
vehicle food was potato salad served to about 11,000 individuals at a barbecue. It was prepared and
stored for up to 16 hours at improper holding temperatures prior to serving; the serovar isolated
was S. Newport. It may be noted from Figure 26–2 that S. Typhimurium has been the single most
625
In dry foods, S. Montevideo was found to be more resistant than S. Heidelberg when inoculated
into dry milk, cocoa powder, poultry feed, meat, and bone meal.
29 Survival was greater at a w 0.43 and
0.52 than at a w 0.75.
The Salmonella Food-Poisoning Syndrome
This syndrome is caused by the ingestion of foods that contain significant numbers of non-hostspecific species or serotypes of the genus Salmonella. From the time of ingestion of food, symptoms
usually develop in 12–14 hours, although shorter and longer times have been reported. The symptoms
consist of nausea, vomiting, abdominal pain (not as severe as with staphylococcal food poisoning),
headache, chills, and diarrhea. These symptoms are usually accompanied by prostration, muscular
weakness, faintness, moderate fever, restlessness, and drowsiness. Symptoms usually persist for 2–3
days. The average mortality rate is 4.1%, varying from 5.8% during the first year of life, to 2% between
the first and 50th year, and 15% in persons over 50 years. Among the different species of Salmonella,S.
Choleraesuis has been reported to produce the highest mortality rate—21% (see Chapter 22).
Although these organisms generally disappear rapidly from the intestinal tract, up to 5% of patients
may become carriers of the organisms upon recovery from this disease.
Numbers of cells on the order of 10
7 –10
9 /g are generally necessary for salmonellosis. That outbreaks may occur in which relatively low numbers of cells are found has been noted.
18 From three
outbreaks, the numbers of cells found were as low as 100/100 g (S. Eastbourne in chocolate) to 15,000/g
(S. Cubana in a carmine dye solution). In general, minimum numbers for gastroenteritis range between
10
5 and 10
6 /g for S. Bareilly and S. Newport to 10
9 –10
10 for S. Pullorum.
8
Salmonella Virulence Properties
Although an enterotoxin and a cytotoxin have been identified in pathogenic salmonellae, they seem
to play only a minimal (if any) role in the gastroenteritis syndrome. The virulence mechanisms of the
salmonellae continue to be unravelled, and summaries of what is known are presented in Chapter 22
along with other Gram-negative foodborne pathogens. A synopsis of the early history of salmonellae
pathogenesis can be found in the previous edition of this text.
Incidence and Vehicle Foods
The precise incidence of salmonellae food poisoning in the United States is not known. However, the two largest recorded outbreaks of salmonellosis occurred under rather unusual circumstances. The largest occurred in 1994 and it involved more than 224,000 persons.
23 The vehicle
food was ice cream produced from milk that was transported in tanker trucks that had previously hauled liquid eggs. The serovar was S. Enteritidis, and cases were seen in at least 41 U.S.
states. The next largest outbreak occurred in 1985 and involved close to 200,000 persons.
48 (See
Fig. 26–1 and Fig. 26–2.) The vehicle was 2% milk produced by a single dairy plant in Illinois,
and S. Typhimurium was the etiological agent (see Figures 26–1 and 26–2). The third largest outbreak occurred in 1974 on the Navajo Indian Reservation, when 3,400 persons became ill.
26 The
vehicle food was potato salad served to about 11,000 individuals at a barbecue. It was prepared and
stored for up to 16 hours at improper holding temperatures prior to serving; the serovar isolated
was S. Newport. It may be noted from Figure 26–2 that S. Typhimurium has been the single most