Eradication 75

Eradication

As the number of new cases continues to dwindle, one of the most important questions for the future is whether SARS can be eliminated or eradicated from its new human host. Experience with many other infectious diseases, including smallpox and poliomyelitis, has demonstrated that complete eradication of an infectious disease is possible only when three precise requirements can be met (WHO Update 84):

1)An effective intervention capable of interrupting transmission – ideally, a vaccine – must be available.

2)Easy-to-use diagnostic tools are needed, with sufficient sensitivity and specificity to detect levels of infection that can lead to transmission of the disease.

3)Finally, infection of humans must be essential to the life-cycle of the causative agent – if the chain of human-to-human transmission is broken, the agent cannot survive. Existence of an animal reservoir greatly complicates eradication, but does not preclude it, provided that interventions exist to break the chain of transmission in the animal species as well.

To achieve eradication at the global level, the control intervention must be safe, simple, and affordable. Current control measures for SARS, including case detection and isolation, tracing and follow-up of contacts, and quarantine, are effective but extremely time-intensive, costly, and socially disruptive. Few, if any, countries can sustain such efforts over time (WHO Update 84).

Outlook

During the first epidemic of SARS, most countries had to deal with a small number of imported cases. When these cases were promptly detected, isolated, and managed according to strict procedures of infection control, further spread to hospital staff and family members either did not occur at all or resulted in a very small number of secondary infections (Chan-Yeung).

In countries with significant transmission of the SARS virus, the local outbreaks of Spring 2003 have been controlled; however, second out

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breaks, such as those in Taiwan and Toronto, teach that complacency must be avoided.

Many lessons have been learned:

Only one individual is required for an outbreak. One single infected individual is sufficient to test the flexibility of modern healthcare systems to the limit;

The SARS virus is sufficiently transmissible to cause a very large epidemic if unchecked, but not so contagious as to be uncontrollable with good, basic public health measures (Dye);

The unsuspected SARS patients will be the greatest challenge in medicine if SARS cannot be eradicated

Many questions remain unsolved:

Will SARS maintain itself, with new foci appearing here and there?

Will SARS establish itself as an endemic illness, perhaps with seasonal patterns? (Holmes)

Will SARS remain confined to the areas where it is currently located, or will it spread around the world?

What would the virus do in the developing countries?

Would the transmission patterns be different if the virus was introduced into populations with a high prevalence of immunocompromised patients, i.e., people living with HIV?

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