|Botulism is a severe neuroparalytic disease caused by toxin produced by
Clostridium botulinum, an anaerobic spore-forming bacillus. Physicians
in Norway are required to notify the National Institute of Public Health
(NIPH) of cases of botulism immediately by telephone and by mail on a special
notification form. The patient's name, age, date of birth, identification
number, and address, and the suspected source of infection should be reported.
NIPH has a database of all surveillance data from 1975. Foodborne botulism
is rare in Norway and infant and wound botulism were reported for the first
time in 1997 (1). A recent increase in the number of cases of botulism in
Norway (figure 1) has highlighted the need to maintain vigilance both to
improve case recognition and to sustain preventive measures.
Foodborne botulism in Norway is typically associated with the consumption
of rakfisk, a traditional half-fermented fish dish eaten mainly
at Christmas. Cases usually occur as small family outbreaks of one to
eight cases, during the winter months November to February. Twenty-two
cases, representing 10 outbreaks, were reported to the NIPH between 1975
and 1997. Thirteen patients were men and nine were women. The average
age of the patients was 44 years (range 23 to 73 years). All cases of
foodborne botulism were either type E or type B.
Four cases of foodborne botulism were reported in 1997, three from the
same family. Two of the three cases had only mild symptoms (dry mouth,
dizziness and blurred vision). One developed paralytic symptoms, especially
in the upper extremities, and dyspnoea. He was admitted to hospital, treated
with botulinum antitoxin, and recovered over a period of several months.
All three had eaten the same rakfisk before they fell ill,
and botulinum toxin type E was identified in the leftover fish (2).
In 1997, a baby boy aged 3 months was admitted to hospital with neurological
symptoms of gradual onset. The disease started with obstipation, and within
one week the baby became hypotonic, lost his sucking reflex, and developed
dilated unreactive pupils. Patellar and achilles tendon reflexes disappeared,
and he needed mechanical ventilation for respiratory distress for 16 days.
The baby was in hospital for 3 months, but by the age of 10 months he
had completely recovered. Botulinum toxin type A was found in his serum.
He had been given imported honey before the onset of his illness, and
C. botulinum spores were found in the honey.
Three cases of wound botulism were reported in 1997, all of whom were
injecting drug users (IDUs). Botulinum toxin was not found in serum specimens,
and bacterial cultures of wounds were negative for C. botulinum,
but their symptoms were typical of botulism and alternative diagnoses
(e.g., Guillain-Barré syndrome) were ruled out by clinical and neurophysiological
examination. They were diagnosed with botulism, and treated with botulinum
antitoxin. The most severely affected patient was mechanically ventilated
for two weeks and remained in hospital for six weeks. Fourteen weeks after
the onset of his illness, he still had mild symptoms, such as ptosis,
and his physical condition was weaker than before the disease. Samples
of the heroin used by two of the cases were tested, but no spores were
detected and there was no growth of C. botulinum.
Home-canned vegetables are the commonest source of foodborne botulism
worldwide. In northern countries, however, fish contaminated with type
E spores is the most important source (3). Rakfisk is usually
prepared commercially, but home preparation is still popular. In normal
preparation, salt (6% to 8% of the weight of the fish) and sugar are added
to the gutted fish, which is then put into a pot under pressure. The pot
is stored in a cool place (58 ºC) and eaten without cooking after
two to three months. In the family outbreak described above, the fish
was first fermented in a cellar at 13°C for three weeks, and only then
refrigerated at 7°C. Such conditions allow C. botulinum to germinate
and produce toxin.
To prevent botulism associated with rakfisk consumption,
the production process should be controlled carefully to minimise the
risk of germination of C. botulinum. Temperature during fermentation
should be lower than 8°C throughout, and the salt concentration should
exceed 5% (4).
Infant botulism is a special form of the foodborne disease, which almost
exclusively affects children under 1 year of age. Clinical severity varies
widely from mild symptoms to sudden infant death. The disease is caused
by growth of C. botulinum, and toxin production, in the intestine.
Honey is the only recorded source of infant botulism, though in most cases
the source has not been found (5). Honey is not an essential part of the
infant diet, and should not be given to children under 1 year of age (6).
Adults who have altered gastrointestinal anatomy and microflora may suffer
a similar illness (7).
Wound botulism among IDUs was reported for the first time in New York
in 1982 (8). It is caused by toxin produced by C. botulinum growing
in injection sites or wounds. The symptoms do not begin as abruptly as
in foodborne botulism, because the toxin is released into the circulation
more gradually. The source of C. botulinum in IDUs is not known
precisely. The spores could be in the drug itself, or in the needles and
syringes, and so injected; on the other hand the infection might be due
to colonisation of existing wounds. In a case control study in California,
subcutaneous or intramuscular injection of black tar heroin
was the only behaviour significantly associated with wound botulism (9).
Such injection would provide good growth conditions for C. botulinum
at the injection site. The authors suggested that the source of C.
botulinum was the drug itself.
We do not believe that all of the cases of botulism in Norway are known
to the NIPH. The severity of symptoms depends on the amount of toxin ingested.
Mild cases may not seek medical attention at all. If a patient presents
with only nausea and mild neurological symptoms, the possibility of botulism
may not occur to the physician, with the result that the case is not notified.
It is important that physicians and public health doctors be aware of
this potentially fatal disease. The earlier the treatment is started the
better is the outcome, and botulism is preventable.
* European Programme for Intervention Epidemiology Training (EPIET, a
programme funded by DGV of Commission of European Communities).