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Botulism in Alaska



As already mentioned, botulism is a public health emergency and health care providers should report all suspected cases to the Alaska Division of Public Health, Section of Epidemiology. Since 1947, the Alaska Area Native Health Service of the Indian Health Service, the Arctic Investigations Program of the U.S. Centers for Disease Control and Prevention (CDC), and the Alaska Division of Public Health have conducted epidemiologic investigations of all patients with possible botulism. Although early records contain less detail, results of the investigations have been collected and analyzed.


For this monograph, the definitions of confirmed and possible botulism explained in Table 5 were used. Botulism cases may go undiagnosed and therefore unreported if a person either does not seek medical care or the diagnosis is not considered. However, since laboratory confirmation requires testing which is only available from the CDC, the botulism cases summarized here likely represent all confirmed cases in Alaska from 1947 through 1997.

Table 5. Definitions of confirmed and possible botulism
A confirmed case of botulism was any person in Alaska with a compatible illness having one or more of the symptoms listed in Table 1 who met at least one of the following conditions:
  1. The identification of botulism toxin in an implicated food or in serum, stool, gastric aspirate, or vomitus collected from the person.

  2. The isolation of C. botulinum organism from the person's stool culture.

  3. A history of eating the same incriminated food as a person meeting one of the first two conditions.

A possible case of botulism was a person with a compatible illness following consumption of food frequently associated with botulism but who did not meet any of the above conditions.

Laboratory testing of clinical specimens and food samples was conducted at the CDC, Atlanta, Georgia using the mouse bioassay method described by the Center for Disease Control (1979).

An outbreak was the occurrence of botulism (whether confirmed or possible) among one or more persons who had eaten a common food.

Forty-three possible cases of botulism (from 25 outbreaks) which occurred between 1947 and 1997 were excluded from the analysis presented here. Information on many of these can be found in a publication by Wainwright et al. (1988).


From 1950 to 1997, 105 confirmed outbreaks of foodborne botulism involving 214 persons occurred in Alaska (there were no confirmed cases during 1947-1949) (Figure 1). Almost exactly half (51/105) of the outbreaks had more than one case and seven outbreaks had five or more cases. The largest outbreak, with nine cases, occurred in 1973.

All cases occurred in Alaska Natives. The average annual incidence among Alaska Natives increased from 3.5 cases/100,000 population during 1950-1954 to 10.7 cases/100,000 during 1995-1997 (Table 6). Reasons for the increase are unknown but may relate to changes in food preparation practices or improved recognition of mild cases.

The mean age of persons at onset of foodborne botulism, 43 years, did not change substantially during 1950-1997 (correlation coefficient=0.17; r2=0.03). Illness was relatively uncommon in children - only 11 cases were 12 years of age or less.

There have been a total of 19 deaths for an overall case fatality rate of 9%. The case fatality rate declined from 31% during 1950-1959 to 5% during 1990-1997.


Figure 1. Botulism outbreaks, cases and deaths, by year; Alaska, 1950 - 1997
Figure 1. Outbreaks by Year


Table 6. Confirmed botulism cases, incidence, deaths and case fatality
               rate by 5-year intervals; Alaska, 1950 - 1997
Interval (years) Number of Cases Incidence* Number of Deaths Case Fatality Rate
1950 - 1954 6 3.5 1 0.16
1955 - 1959 7 3.6 3 0.43
1960 - 1964 3 1.3 3 1.00
1965 - 1969 1 0.4 0 0.00
1970 - 1974 15 5.6 1 0.07
1975 - 1979 28 9.4 5 0.18
1980 - 1984 19 5.6 0 0.00
1985 - 1989 49 12.6 2 0.04
1990 - 1994 54 11.7 4 0.09
1995 - 1997 32 10.7 0 0.00
1950 - 1997 214 6.7 19 0.09
* Annual incidence per 100,000 Alaska Natives. Mid-period population was used for each interval except
   1950-1997 which was calculated by averaging the individual intervals.


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Seasonality, types, and location

Outbreaks occurred in every month of the year (Figure 2). Slightly over half of the outbreaks (55 of 100 with a known date) occurred during June through September. Type E botulism was by far the most frequent type, accounting for 82% (86/105) of the outbreaks, 79% (169/214) of the cases, and 84% (16/19) of the deaths.

Types A and B botulism caused 9 and 32 cases, respectively.

Botulism occurred predominantly in coastal villages in the western and southeastern parts of the state (Figure 3).

Figure 2. Botulism outbreaks, cases and deaths, by month of onset;
               Alaska, 1950 - 1997*
Figure 2. Outbreaks by Month
    * Month of onset unknown for 10 cases (5 outbreaks and 2 deaths).


Figure 3. Location of botulism cases; Alaska, 1950 - 1997
Figure 3. Cases by Location
Location No. of cases Location No. of cases Location No. of cases
1) Barrow
2) Point Hope
3) Kivalina
4) Kotzebue
5) Noorvik
6) Selawik
7) Brevig Mission
8) Teller
9) Nome
10) Golovin
11) Koyuk
12) Shaktoolik
13) Savoonga
14) Stebbins
15) Saint Michael
16) Alakanuk
17) Sheldon Point
18) Scammon Bay
19) Hooper Bay
20) Chevak
21) Newtok
22) Nightmute
23) Chefornak
24) Kipnuk
25) Kwigillingok
26) Tuntutuliak
27) Kasigluk
28) Tuluksak
29) Akiachak
30) Kwethluk
31) Napaskiak
32) Napakiak
33) Eek
34) Goodnews Bay
35) Togiak
36) Twin Hills
37) Manokotak
38) Tuklung
39) Kanakanak
40) Ekuk
41) New Stuyahok
42) Egegik
43) Anchorage
44) Palmer
45) Glennallen
46) Hoonah
47) Juneau
48) Angoon
49) Sitka
50) Kake
51) Klawok
52) Hydaburg
53) Ketchikan
54) Metlakatla


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In 53 (50%) of the outbreaks and 109 (51%) of the cases, an implicated food sample tested positive for botulism toxin (Table 7). The remaining outbreaks were confirmed as a result of either a positive toxin assay of a patient's serum, stool, or gastric contents; or a positive culture of a patient's stool specimen for C. botulinum organism. When food samples did not contain botulism toxin, the results of the epidemiologic investigation were used to identify the food most likely responsible for the outbreak.

Table 7. Foods implicated in confirmed botulism outbreaks;
               Alaska, 1950 - 1997
Type of Food Number Implicated Number Toxin Positive
Sea Mammal
   Salmon eggs
   Salmon Heads
   Salmon, other
Land Mammal
   Beaver tail
4 4
Other 5 2
Unknown 5 0
Total 105 53


A variety of traditional Alaska Native foods including seal, whale, and fish have been implicated (Table 7). The commonest method of preparation was fermentation - a process in which fresh food was allowed to putrefy for 1 to 2 weeks in either a pit in the ground or a closed or air-tight container (Table 8). No cases of foodborne botulism in Alaska have been associated with home canned food.

Table 8. Method of preservation for implicated foods in confirmed
              botulism outbreaks; Alaska, 1950 - 1997
Method of Preservation Number Implicated
Fermentation 60
Drying 7
Rendering (oil) 20
Salting 1
Other/Unknown 17
Total 105


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Prevention and control of foodborne botulism in Alaska remains problematic. Although a multivalent toxoid which includes types A, B, and E is available, immunization of the entire population is not practical or indicated. Strategies for controlling foodborne botulism fall largely into two approaches: (1) reducing contamination of food with C. botulinum spores and preventing toxin production in food, and (2) early identification of botulism cases. Reducing contamination and preventing toxin formation are difficult to achieve. Subsistence hunting and fishing remain an integral part of Alaska Native life and botulism spores, particularly type E, are ubiquitous in Alaska.

In addition, the traditional methods of preparation of fermented foods produce a flavor and texture that is altered and generally unacceptable if procedures such as cooking are added to the process. However, the traditional methods have been made even more unsafe with the current use of airtight containers - glass and plastic jars, buckets, and plastic bags and the practice of accelerating the process by fermenting food in a warm environment. Attempts to educate preparers of traditional fermented foods in methods to reduce the risk of botulism have not as yet been successful.

In contrast to the lack of success in controlling foodborne botulism by educating the preparers, educating health care providers to recognize botulism early in its clinical course and to report cases promptly has proved effective in limiting adverse outcomes. Educational efforts directed toward eliciting a careful food consumption history, having a high level of suspicion when confronted with illness with gastrointestinal and neurologic symptoms, and use of the "diagnostic pentad" have been the mainstay of control efforts in Alaska. These educational efforts combined with rapid epidemiologic investigation of suspected cases, prompt supportive care, and the availability of botulism antitoxin may be responsible for the decrease of the case fatality rate.

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Other aspects of botulism in Alaska

C. botulinum spores are widely distributed in the Alaska environment. Miller, Clark, and Kunkle (1972) demonstrated type E botulism toxicity in enrichment cultures of 17 of 23 beach soil samples collected in the Kotzebue region. Other investigators (Houghtby and Kaysner 1969) detected low level intrinsic contamination of Alaska salmon with type E C. botulinum spores. Among 589 pink, sockeye, chinook, and chum salmon collected from Bristol Bay, Southeastern Alaska, Kodiak, and the Yukon River, 6 (1%) had gill specimens yielding positive cultures for type E toxin. None of 494 viscera specimens were positive.

Probably the most extensive environmental survey for C. botulinum in Alaska was conducted by Miller (1975). Samples of beach soil, ocean water and sediments, salmon, and marine mammals were collected from 23 sites in both interior and coastal areas. As shown by the results summarized in Table 9, type E C. botulinum spores were widely distributed. No other type of C. botulinum was identified and, with one exception, no specimens from north of Point Hope were positive.

Shaffer et al. (1990) surveyed Alaska Native food consumption patterns and preparation practices in the Bristol Bay region in 1987. In four Yupik villages, they found that fermented foods were regularly prepared by 15% of high school students, 71% of students' parents, and 80% of their grandparents. Fermentation practices appeared to have changed from the traditional method of using a clay pit in the ground. Only 13% of preparers reported that they used the traditional method to ferment fish heads while 42% used a wooden barrel above ground, 38% used a wooden barrel in the ground, and 8% used a plastic bucket above ground. These findings suggested that changes in food preparation practices have resulted in fermentation taking place in warmer conditions which are known to favor the production of botulism toxin.

Table 9. Summary of environmental testing for Clostridium botulinum spores in Alaska, 19751
Type of Sample Number
Beach Soil
   River or Lake
Positives from Kotzebue, Kotzebue Sound, Southeast.
Negatives from north coast, Aleutians, Kenai Peninsula, Prince William Sound.
Positives from Yukon-Kuskokwim Delta, Interior, Kenai Peninsula, Prince William Sound.3
91% of samples from Kotzebue were positive.
Other positives from Kodiak and Southeast. 
All samples were from the Kotzebue area.
   Marine Mammals
Positives were gill specimens from Kotzebue and Bethel.
Negatives were flesh, viscera, and roe from Bethel.
The positive was a beluga whale. Negatives were walrus, sea otter, and harbor, ringed and bearded seals.4
  1. All data from Miller (1975).
  2. All positive samples had type E botulism toxicity.
  3. One positive sample was from a pond approximately 50 miles south of Prudhoe Bay. Five of the remaining six positive samples were collected from areas directly associated with salmon or salmon processing.
  4. Animals were harvested in the Chukchi Sea, Bering Straits, and Kotzebue Sound. Colonic contents were anaerobically cultured and tested for botulism toxicity.


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Unanswered questions

Many questions concerning botulism in Alaska remain unanswered. Future studies may improve our understanding of botulism pathophysiology, treatment, and ecology. Important concerns include:
  • Can people develop immunity to botulism as a result of consuming food which contains toxin?
  • Why is the clinical course of botulism patients in Alaska milder than that of patients with foodborne botulism in other states?
  • What is the prevalence of botulism toxin in traditional Alaska Native foods?
  • Can C. botulinum spores be isolated from the feces of asymptomatic persons who regularly consume traditional Alaska Native foods?
  • Is the apparent increase in botulism incidence due to better recognition, improved reporting, changes in food preparation practices, or other factors?
  • Does illness severity correlate with circulating antitoxin levels found after treatment?

Botulism remains a fascinating illness which challenges the clinician to make a diagnosis using the classic elements of medical practice--history and physical examination. Once the diagnosis is made the patient's life may well have been saved. Clinical opportunities like this do not come often, but can be extremely satisfying if appropriately handled. Practitioners who care for Alaska Natives have a reasonably high likelihood of encountering botulism. They should be alert to this possibility and act decisively if the diagnosis is entertained.

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