Quick Facts...
- The Western United States has one of the highest incidences of botulism
in the United States because of soil and high altitude.
- Conditions that favor botulism include a high-moisture, low-salt,
low-acid environment in which food is stored without oxygen or refrigeration.
- Anaerobic conditions can develop in canned foods, smoked fish, sausages
and some cooked foods.
- Botulism can be controlled in home-canned foods if home canners are
made aware of the dangers and how to prevent it.
Four classifications are being used currently in the United
States to discuss botulism in humans. These are 1) food-borne
botulism, caused by consuming food containing botulinal toxin 2)
infant botulism, caused by production of botulinal toxin after
germination and growth of the spores within the infant's
intestines; 3) wound botulism, resulting from germination and
growth of Clostridium botulinum within a wound; and 4)
undetermined botulism, occurring in persons older than 12 months,
in which no food or wound is implicated.
The majority of reported cases of botulism have
traditionally been food-borne in nature. In recent years around
30 cases per year have been reported.
Infant botulism was first recognized in 1976. Currently, around 100 cases are
reported each year. The age range has been 22 days to 14 months.
Although the possibility of wound botulism was recognized as early as 1920,
no actual cases were reported until 1943. Since the 1980s, the incidence
has steadily increased, mostly among injection-drug users.
The Botulism Organism
There currently are seven known types of Clostridium
botulinum bacteria. These differ in such characteristics as
proteolytic activity, tolerance to salt and reduced water activity,
minimum growth temperature and resistance to destruction by heat.
The proteolytic type A, B and F strains produce very
heat-resistant spores which are a major concern in the processing
of low-acid foods. These types digest proteins in foods and
produce a foul odor that may warn Consumers of spoilage.
The nonproteolytic type B, E and F strains can grow at
refrigerated temperatures, but produce spores of very low heat
resistance. These types cause problems primarily in pasteurized
or unheated foods. Because they are nonproteolytic, no off-odor
or evidence of spoilage may be produced with toxin development.
Type C strains cause botulism in birds, turtles, cattle,
sheep and horses. Type D is associated with forage poisoning of
cattle and sheep in Australia and South Africa. No outbreaks of
type G have been reported; however, type G has been isolated in
cases of sudden and unexpected death in humans.
Inactive Clostridium botulinum spores are found in soil and
water throughout the world. In the spore form, these bacteria are
relatively harmless. The problem occurs when the spores germinate
into vegetative or actively growing cells. As the vegetative
cells grow they become overpopulated and begin to die. As they
do, they produce the deadly neurotoxin that causes botulism.
Type A toxin is more lethal than types B and E. The toxin is
a protein which can be inactivated by heating at 180 degrees F
for 10 minutes. The toxin can be absorbed into the blood stream
through the respiratory mucous membranes as well as through the
wall of the stomach and intestine.
Several conditions must be present for the germination and
growth of Clostridium botulinum spores. Acid level is a primary
factor. Acidity is measured on a pH scale of 0 to 14, with 7
considered neutral, 0 to 7 acidic and 7 to 14 alkaline. A pH near
7 or neutral favors the growth of Clostridium botulinum, while
growth is inhibited at a pH of 4.6 or lower. The pH of a food
also has an influence on the amount of heat necessary to kill the
spores of Clostridium botulinum. The higher the pH (lower the
acid level), the greater the amount of heat needed to kill the
spores.
A second important factor affecting the growth and toxin
production of Clostridium botulinum is temperature. Proteolytic
types grow between temperatures of 55 and 122 degrees F, with
most rapid growth occurring at 95 degrees F. Nonproteolytic types
grow between 38 and 113 degrees F, with an optimum for growth and
toxin production at about 86 degrees F. For these types,
refrigeration above 38 degrees F may not be a complete safeguard
against botulism.
Another important condition affecting the growth of
Clostridium botulinum is the present of oxygen. These organisms
can't grow if air or free oxygen is present in their
microenvironment (the area immediately next to them). This area
is so small that it is not readily observed. Therefore, it is
possible to have conditions develop in a food system or wound
whereby it appears that lots of air is available, but in reality
there are areas where no air is present and anaerobic organisms,
such as Clostridium botulinum, can develop. Anaerobic conditions
develop when food is canned. If the food is not heated enough to
kill the spores of Clostridium botulinum, the spores will
germinate and grow during subsequent storage of the food.
Canning is not the only condition in the manufacture and preservation of foods
in which anaerobic conditions can develop. Smoked fish can develop anaerobic
conditions in the visceral cavity and under the skin. The interior of
sausage also may become anaerobic during the preservation process. Anaerobic
conditions capable of supporting the growth of C. botulinum also
have developed in such foods as chopped garlic in oil, foil-wrapped baked
potatoes, sauteed onions, turkey loaves, meat stews and pot pies left
at room temperature or in a warming oven overnight. In these cases the
original baking killed competing organisms and eliminated much of the
oxygen in the micro-environment under the crust, foil or buttery coating.
Subsequent storage at warm temperatures created an ideal environment for
the germination and growth of botulinum spores. For these types of foods,
growth of Clostridium botulinum is inhibited by storage at a
low temperature (below 38 degrees F) and/or the use of a preservative,
such as sodium nitrite.
Food-Borne Botulism
Food-borne botulism was first identified in Europe during
the 1800s as a problem in sausages. The sausages probably were
slightly preserved with salt and smoke. Refrigeration was
nonexistent or dependent on seasons of the year. Because of the
great problem with sausages, the disease was named botulism after
the Latin word for sausage, botulus.
In the 1900s, refrigeration practices improved and sausages
no longer caused a major problem with botulism. However, at this
same time, the technology and containers for canning became
available. Almost immediately, botulism became a problem in
canned foods. By 1926, most of the problems in the commercial
canning industry had been solved. Since that time, most of the
outbreaks of food-borne botulism in the United States have been
caused by improperly home-canned foods, mostly fish and
vegetables, such as string beans, corn, beets, spinach, asparagus
and chili peppers.
Although low-acid vegetables and fish have been the chief
culprits, tomatoes, tomato-based mixtures and such fruits as
figs, apricots, pears, peaches, applesauce, persimmons and
mangoes also have been involved. In some of these cases
inadequate processing permitted the growth of molds, yeasts or
bacteria, which in turn raised the pH of the food sufficiently to
permit the growth of C. botulinum.
In some of these cases, molds or bacteria grew due to poor
processing and reduced acidity. In others, reduced acidity may
have been due to differences in variety or in the degree of
ripeness, pointing up the fact that overripe tomatoes and fruits
should not be selected for home canning. With fruits, the syrup
added before processing does not become acidic until acid
diffuses out of the food. This may take some time if the fruit is
not heated (processed) enough.
Colorado and other states in the West have higher per capita rates of
food-borne botulism than other parts fo the United States. One contributing
factor is that the soil in the western United States from the Rocky Mountains
to the Pacific Ocean contains a particularly high count of Type A Clostridium
botulinum spores, the type of spores that produce the toxin most
dangerous to humans.
A second factor is the higher altitude. The temperature of
boiling water decreases as the altitude increases. Thus, the
temperature at which foods are processed is lower. To compensate,
the canning pressure for low-acid foods must be increased by 1/2
pound for every 1,000 feet rise in elevation. For example, at
5,000 feet vegetables must be pressure canned at 12-1/2 pounds
pressure per square inch rather than the usual 10 pounds
recommended in canning instructions designed for sea level
canning. Forgetting to make these changes leads to
underprocessing and an increased risk of botulism.
Infant Botulism
Unlike food-borne botulism, which is caused by ingestion of
pre-formed botulinal toxin, infant botulism is presumed to be
caused by ingestion of viable spores that later grow and produce
toxin in susceptible infants, mostly under 6 to 8 months of age.
Because C. botulinum spores are found in the soil everywhere, the
probability of ingesting the spores from Garden soil, dust in the
air, and such sources as vacuum cleaner dust is quite high. The
only food item thus far associated with cases of infant botulism
has been honey, although the possibility exists for contamination
with the spores from any raw or unprocessed food, especially if
it has not been carefully washed.
Symptoms
Symptoms of food-borne botulism usually appear within 18 to 36hours
after the contaminated food is eaten, but the time can vary from six hours
to 10 days. The most significant symptoms are blurred double vision and
difficulty in swallowing and speaking. Fever is absent early in the disease.
For some types of the disease, early symptoms may be
gastrointestinal in nature (nausea, vomiting, abdominal pain,
constipation, cramps, headache, fullness) and lead to a false
diagnosis of appendicitis, bowel obstruction or heart attack.
Symptoms of infant botulism include constipation, followed by general
weakness, feeding and swallowing problems, weak or altered cry, loss of
motor tone and poor head control. The syndrome can evolve in anywhere
from 6 hours to one week or more and ranges in severity from no more than
minimal constipation to sudden death. In cases of the latter, infant botulism
is thought to account for at least some of the reported cases of Sudden
Infant Death Syndrome.
Treatment
Unless treatment of food-borne botulism is initiated
promptly at the onset of the symptoms, death may result within
three to seven days. Improved detection methods and the ready
availability of antitoxins have reduced the high death rate to
around 10 percent in recent years.
Most state health departments offer 24-hour assistance in diagnosing
and obtaining antitoxin for treatment of botulism. In Colorado, contact
the State Health Department at (303) 692-2000 weekdays or (303) 370-9395
weekends and evenings if botulism is suspected.
Treatment of food-borne botulism consists primarily of 1)
removing any unabsorbed toxin in the digestive tract, 2)
neutralizing the circulating toxin with an antitoxin as quickly
as possible, and 3) keeping a patient breathing by a mechanical
respirator (iron lung) as necessary. Recovery may take several
weeks to months.
Treatment of infant botulism is somewhat different than that
of food-borne botulism. Antitoxin generally is not used because
of potentially hazardous side effects on young infants. Rather,
comprehensive supportive care in the hospital for the course of
the disease, usually three to four weeks, is the usual treatment.
Prevention
Botulism can be controlled if Consumers are aware of the
dangers and take steps to prevent spoilage in home-canned and
home-cooked foods. Here are some important tips to remember:
- Clean foods well before cooking or processing. This reduces
but does not remove all bacteria. Bacteria are still present
in nearly every pint or unit of food to be cooked or canned.
- Be sure all home canning methods are up-to-date with current
research-based recommendations and are properly adjusted for
altitude.
- Process all home-canned meats and vegetables, with the possible exception
of tomatoes, in a steam pressure canner at 240 degrees F for the time
recommended in a current USDA research-based publication. At sea level,
a pressure of 11 pounds per square inch (psi) is necessary to reach
240 degrees F. With each 1,000 feet rise in altitude an additional 1/2
psi is needed to achieve 240 degrees F. When using a weighted pressure
gauge, the 15 pound weight must be used at all altitudes in Colorado.
- Acid foods, such as tomatoes and fruits, if properly
selected and processed, do not support the growth of
Clostridium botulinum and may be canned in a boiling water
bath if current, research-based instructions are followed.
The addition of acid in the form of lemon juice or citric
acid is recommended in all tomato products canned in a
boiling water bath as a precautionary measure.
- Before using home-canned food, critically examine the
product and container. A bulging lid or leaking jar are
signs of spoilage. When you open the jar, look for other
signs of spoilage such as spurting liquid, an off odor or
mold.
- As an added precaution, boil all home-canned vegetables and
meats without tasting for 10 minutes plus one minute per
1,000 feet above sea level (15 minutes at 5,000 feet). Boil
home-canned spinach and corn 20 minutes before tasting. If
the food looks spoiled, foams or has an off odor during
heating, discard it.
- Dispose of all spoiled food in a place where it will not be
eaten by children or pets. One sure way to prevent the
spread of toxin is to boil suspect foods 30 minutes before
disposing. This will ensure destruction of any toxin that
might be present and prevent its spread.
- See 9.300, Bacterial food-borne illness, for more tips on
avoiding food spoilage.
- Given the widespread nature of C. botulinum spores in the
soil, especially in the western part of the United States, complete
prevention of infant botulism is probably not possible. However, measures
that can reduce the incidence include avoidance of honey and protection
from excessively dusty or muddy conditions among infants under 1 year
of age.
References
- CDC. 1998. Botulism in the United States. 1899-1996: Handbook for
Epidemiologists, Clinicians, and Laboratory Workers. Atlanta, GA:
Centers for Disease Control and Prevention.
- Sobel, J., Tucker, N., Sulka, A., McLaughlin, J., and Maslanka, S.
2004. Foodborne Botulism in the United States, 1990-2000. Emerging
Infectious Diseases, 10:1606-1611.
- Summary of Notifiable Diseases, United States, 2000. Morbidity
and Mortality Weekly Report, 49 (53) 1-100, June 14, 2002.
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