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Sverdlovsk anthrax outbreak 1979 – outbreak investigation

Sverdlovsk anthrax outbreak 1979 - outbreak investigation
SPEAKER: Following the first deaths, a public health response to the outbreak was initiated. The first part of the public health response involved collating all known cases of the outbreak and identifying which cases had died. As the epidemic regressed, the pattern of cases, date of symptom onset, and date of death emerged. This epidemic data strongly suggested that this was an unusual outbreak of an uncommon disease. Firstly, the average time to case onset and death was seen as unusual for gastrointestinal anthrax and more in keeping with sever inhalational anthrax disease. The chart shone here shows the onset by week commencing the week of the fourth of April 1979 of fatal cases.
As you can see, the majority of cases was seen in the first 14 days of the epidemic. This pattern supported the hypothesis that the outbreak was due to a single exposure event of anthrax rather than a gradual or recurrent exposure over a period of time. This is sometimes referred to as a sporadic outbreak. Of particular interest, new cases of anthrax was seen until 43 days or six weeks after the estimated commencement of the outbreak. This was the first time that such a long incubation period had been observed in human cases of anthrax. And raised many questions about both the nature of the exposure and the features of the anthrax disease itself.
Concurrently, it was also found at the time that animal cases of the disease had occurred as the same time as the human cases classifying this is an epizoonotic outbreak. That animal cases were occurring at exactly the same time as human cases is unusual. Generally speaking, zoonotic disease occurs prior to human cases as the disease finds its way into the human population from the animals over a period of time. This was not seen in Sverdlovsk. Additionally, the animal cases of disease were found to have occurred in a long and narrow band running to south of Sverdlovsk a geographic pattern that would be unusual if anthrax was endemic and difficult to explain by local spread or infection.
In this slide, the day by day occurrence of disease and death during the epidemic can be seen. As mentioned, the majority of cases were seen in the first two weeks as can be clearly seen here. Death was rapid and occurred soon after symptoms of anthrax appeared three to six days after either known or presumed exposure. This pattern is typical of a single point source release of a pathogen such as anthrax. There’s a single outbreak of cases followed by a peak and resolution over time. There’s no sign of ongoing transmission of the pathogen which is consistent with the case of anthrax being at the single exposure.
If anthrax was endemic to the Sverdlovsk region, cases would be seen at a low level during periods where transmission could occur. Anthrax was not endemic to the Sverdlovsk region. Following this event, the public health measures instituted by authorities were assessed to have successfully controlled the outbreak. Authorities stated that the response appeared appropriate for an outbreak of gastrointestinal anthrax due to contaminated sources of meat sold in Sverdlovsk and based on the evidence released to the scientific community that this was seen as a reasonable explanation. Some local experts, micro-like biologists, and infectious disease clinicians, and the international biological warfare expert community at the time, and for many years following were not convinced.
Accusations of a cover were made which were dismissed by the government of the time. They cited reports from the local clinicians, pathologists, and the strange patterns of illness as signs that this was not an outbreak of gastrointestinal anthrax but was in fact an outbreak caused by the airborne release of anthrax. Over the following 35 years, the true story of what happened at Sverdlovsk gradually emerged through the persistent investigations of a number of researchers, clinicians, and intelligence officers. With many questions unanswered and allegations and diplomatic frictions between major powers at the height of the Cold War, it was not until the dissolution of the Soviet Union that more information could be uncovered.
In 1992 and 1993, Michael Meselson and a small team from the USA was granted permission to visit Sverdlovsk and conduct further investigations into the incident. In 1994, Meselson and colleagues published an article in “Science” magazine outlining many previously unknown details of the epidemic. The work concluded that the Sverdlovsk anthrax outbreak was inconsistent with a gastrointestinal outbreak and it was more likely than an accidental release of anthrax from a single point source on the second of April 1979 was responsible for causing the outbreak. Meselson concluded that a military microbiological production facility called Compound 19 was the source of the release.
By meticulously piecing together information gained from a variety of sources and from records previously confiscated by authorities at the time of the incident, the following conclusions were drawn. The key features were individuals who were infected with anthrax worked in a geographically small and well defined region of southern Sverdlosk. The geographic clustering of cases were shaped in a band running across the southern area of Sverdlosk aligned in a roughly north to south direction. Zoonotic cases of anthrax seen at the same time as the human cases occurred in a band extending for up to 50 kilometres in the countryside outside of Sverdlovsk and extending from the band of human cases seen within Sverdlosk.
That the autopsy findings supported diagnoses of inhalation anthrax and not gastrointestinal anthrax in all cases. And that unique weather conditions corresponded with an airborne release of anthrax travelling along the same route of the case locations and supported a single release of anthrax on one day. Meselson went on to conclude that the likely source of the airborne release, a building known as Compound 19, was part of a military industrial estate specialising in researching and producing biological weapons. It was thought that this facility was part of a much larger organisation known as Biopreparat, a secret and massive Soviet bioweapons’ programme designed to produce large quantities of biological weapons for military use.
Russia vehemently counted and argued the allegations raised in the article despite the evidence presented.
The Sverdlovsk anthrax outbreak 1979 – outbreak investigation
In this presentation you will explore aspects of the outbreak investigation during the 1979 Sverdlovsk anthrax outbreak and how it was handled. Specifically this will cover:
  • The key features of the outbreak investigation
  • The geographic distribution of cases, and how these were analysed
  • Features of the cases, animal and human, and interpretation of data
After watching this video, in the comments section below discuss your answers to the following questions:
  1. What activities would you undertake as part of an outbreak investigation into a sudden increase in anthrax cases?
  2. Review the geographic distribution of cases. Do you think that geographic location of cases (animal or human) was important in identifying the affected areas and source of the outbreak?
  3. What does the fact that animal cases occurred at the same time as human cases of anthrax tell you about whether this was a natural outbreak of gastrointestinal anthrax, or an accidental airborne release and outbreak of inhalational anthrax? Does this information support one or the other story?
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Biosecurity and Bioterrorism: Public Health Dimensions

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