Rationale for Poliovirus Laboratory Containment
(Borrowed from WHO's Global Action Plan for Laboratory Containment of Wild Polioviruses – 2nd Edition)

Less than one year after smallpox was eradicated in 1977, two cases occurred in the United Kingdom, both linked to a smallpox laboratory. The index case worked in a room located immediately above the laboratory. Two persons died; the index patient as a result of infection, and the director of the laboratory, who took his own life because of the accident.¹ When polio is eradicated every effort must be made to ensure that wild poliovirus is not similarly transmitted from the laboratory to an increasingly non-immune community.

Polioviruses may be transmitted, in theory, to persons outside the laboratory through contaminated laboratory effluents released into sewage, solid wastes transported to landfills, spent air exhausted to surroundings, or through contaminated workers' skin or clothing. However, transmission through such routes is extremely difficult to document against a background of high levels of immunity acquired through natural infection or immunization.

More readily documented are poliovirus infections of laboratory workers with potential for transmission to the community. From 1941 to 1976 a total of 12 laboratory-associated poliomyelitis cases, including two deaths, were recorded.² | 3 | 4 | 5 Accounts of 7 of the 12 were unpublished. Most cases occurred in the pre-vaccine era and before the advent of cell culture.

The first report of a laboratory-associated infection, published in 1941, described a case of poliomyelitis most likely acquired through washing and grinding infected tissues in preparation for inoculation into monkeys.⁶ Two years later, two laboratory workers were infected with the prototype Lansing (Armstrong) strain while attempting to infect mice.⁷ Two additional reported cases of poliomyelitis in laboratory workers were fatal: one in the United States⁸ and the second in South Africa.⁹

The paucity of reports of laboratory-associated poliomyelitis since vaccines were introduced testifies to the effectiveness of vaccines and vastly improved laboratory facilities, technologies, and procedures.^{10, 11} Nevertheless, recent evidence indicates that the potential remains for transmission of poliovirus from the laboratory to the community. In 1992, a wild-type 1 strain used for IPV production was documented as being transmitted from a worker in a vaccine production facility to his young son.¹² In another incident, a child was reported infected with a prototype strain of type 3 commonly used in laboratories for research or vaccine production. The source of this infection was not determined.

IPV is highly effective in preventing disease, but its use cannot be assumed to prevent silent infection among laboratory workers. OPV provides a more effective barrier but silent infections may still occur. The incidence of poliovirus infections without clinical symptoms among laboratory workers is unknown.

In the absence of fully effective vaccines, appropriate biosafety measures are crucial to prevent poliovirus infection of laboratory workers and subsequent transmission. Absolute containment cannot be assured. Questions of intentional or unintentional non-compliance will always remain. But effective containment, that is, reducing the risk of inadvertent reintroduction of wild poliovirus into the community is a realistic goal.

References

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This page last reviewed October 15, 2002
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