Foodborne Toxico-Infections ◾ 375
Analysis of an Outbreak
In March 1989, 300 of 420 employees became ill after attending a corporate luncheon the previous day. Among the 113 people interviewed, diarrhea, abdominal cramps, and nausea were
reported. The symptoms started between 2 and 18 hours (mean average 9.5 hours) following the
luncheon, and the disease lasted approximately 12 hours. Stool specimens contained high numbers of Clo. perfringens. The menu consisted of chicken, roast beef and gravy, lasagna, and mixed
vegetables. Interviews revealed that 98% of those who ate the roast beef became ill; thus, it was
implicated as the likely source. Examination of the catering facilities revealed poor sanitation and
refrigeration facilities. The roasts, each approximately 19 lb (8.6 kg), were cooked three days before
the luncheon date and kept in the refrigerator. Examination of the remaining roast beef showed
the presence of Clo. perfringens at more than 2 × 10 6 cells/g.
The roasted meat, prepared in advance under inadequate sanitary conditions, stored at improper
temperature, and served without further heating, was associated in this Clo. perfringens gastroenteritis outbreak. The most likely sequence of events was as follows: The raw beef (or the facilities in the
kitchen) served as the source of the bacterium (most probably spores). Roasting the large-size meat did
not kill the spores. Subsequently, during storage for three days under improper refrigeration, it took a
long time for the temperature in the large roasts to drop below 10°C. Thus, the spores germinated and
the cells multiplied rapidly in the protein-rich food and reached a high population before the temperature reached below 10°C. When the roast was served, it had a high number of Clo. perfringens cells.
Following consumption of the roast, the cells sporulated, releasing enterotoxins and producing the
gastroenteritis symptoms in 2–18 hours, which lasted for approximately 12 hours. This outbreak could
have been avoided by proper sanitation, proper cooking, proper and quick refrigeration (10°C or below),
and warming the roast above 60°C before serving.
Bacillus cereus 7
Importance
Bacillus species are widely distributed in nature and food. The genus Bacillus currently consists of at
least 56 genera and 545 species. 8 The Bacillus cereus group (Bac. cereus, Bac. anthracis, Bac. mycoides,
Bac. thuringiensis, Bac. pseudomycoides, Bac. weihenstephanensis, and Bac. medusa) and several other
enterotoxin producing Bacillus are of public health significance. 9 Bac. anthracis causes fatal anthrax in
humans and animals. In humans, the disease can be the cutaneous form, respiratory, or gastrointestinal form. The incidence of foodborne gastroenteritis by Bac. cereus origin is relatively high in some
European countries. In contrast, the incidence is quite low in the United States, where Bac. cereus was
recognized as a causative gastroenteritis agent in 1969. Between 1973 and 1987, 58 outbreaks involving
1123 cases were reported. Both the incidence of outbreaks and number of cases per outbreak were low,
and no fatalities were reported. In 2009 and 2010, a total of 25 outbreaks were reported resulting in 427
cases in the United States. 2 The CDC now estimates about 63,000 Americans suffer from Bac. cereus
food poisoning each year. 3 However, as the symptoms are not severe and last only for approximately 12
hours, many cases may not be reported.
Characteristics
The cells are Gram-positive motile rods, which form endospores in the middle of the cells (Figure
27.2). Cells are sensitive to pasteurization. Spores can survive the high heat treatment used in
Analysis of an Outbreak
In March 1989, 300 of 420 employees became ill after attending a corporate luncheon the previous day. Among the 113 people interviewed, diarrhea, abdominal cramps, and nausea were
reported. The symptoms started between 2 and 18 hours (mean average 9.5 hours) following the
luncheon, and the disease lasted approximately 12 hours. Stool specimens contained high numbers of Clo. perfringens. The menu consisted of chicken, roast beef and gravy, lasagna, and mixed
vegetables. Interviews revealed that 98% of those who ate the roast beef became ill; thus, it was
implicated as the likely source. Examination of the catering facilities revealed poor sanitation and
refrigeration facilities. The roasts, each approximately 19 lb (8.6 kg), were cooked three days before
the luncheon date and kept in the refrigerator. Examination of the remaining roast beef showed
the presence of Clo. perfringens at more than 2 × 10 6 cells/g.
The roasted meat, prepared in advance under inadequate sanitary conditions, stored at improper
temperature, and served without further heating, was associated in this Clo. perfringens gastroenteritis outbreak. The most likely sequence of events was as follows: The raw beef (or the facilities in the
kitchen) served as the source of the bacterium (most probably spores). Roasting the large-size meat did
not kill the spores. Subsequently, during storage for three days under improper refrigeration, it took a
long time for the temperature in the large roasts to drop below 10°C. Thus, the spores germinated and
the cells multiplied rapidly in the protein-rich food and reached a high population before the temperature reached below 10°C. When the roast was served, it had a high number of Clo. perfringens cells.
Following consumption of the roast, the cells sporulated, releasing enterotoxins and producing the
gastroenteritis symptoms in 2–18 hours, which lasted for approximately 12 hours. This outbreak could
have been avoided by proper sanitation, proper cooking, proper and quick refrigeration (10°C or below),
and warming the roast above 60°C before serving.
Bacillus cereus 7
Importance
Bacillus species are widely distributed in nature and food. The genus Bacillus currently consists of at
least 56 genera and 545 species. 8 The Bacillus cereus group (Bac. cereus, Bac. anthracis, Bac. mycoides,
Bac. thuringiensis, Bac. pseudomycoides, Bac. weihenstephanensis, and Bac. medusa) and several other
enterotoxin producing Bacillus are of public health significance. 9 Bac. anthracis causes fatal anthrax in
humans and animals. In humans, the disease can be the cutaneous form, respiratory, or gastrointestinal form. The incidence of foodborne gastroenteritis by Bac. cereus origin is relatively high in some
European countries. In contrast, the incidence is quite low in the United States, where Bac. cereus was
recognized as a causative gastroenteritis agent in 1969. Between 1973 and 1987, 58 outbreaks involving
1123 cases were reported. Both the incidence of outbreaks and number of cases per outbreak were low,
and no fatalities were reported. In 2009 and 2010, a total of 25 outbreaks were reported resulting in 427
cases in the United States. 2 The CDC now estimates about 63,000 Americans suffer from Bac. cereus
food poisoning each year. 3 However, as the symptoms are not severe and last only for approximately 12
hours, many cases may not be reported.
Characteristics
The cells are Gram-positive motile rods, which form endospores in the middle of the cells (Figure
27.2). Cells are sensitive to pasteurization. Spores can survive the high heat treatment used in