SARS, emerging infections, and bioterrorism preparedness

The response to the 2002–03 outbreak of severe acute respiratory syndrome (SARS), although effective, was hindered by initial confusion about the identity of the causative pathogen,¹ uncertainty about the epidemiology of transmission and spread,² and difficulties with the flow of information owing to political rivalries.³ Recurrence of the SARS epidemic in Toronto highlighted the potential difficulties of containing similar outbreaks of unfamiliar and highly contagious organisms.⁴

Naturally occurring diseases such as SARS offer valuable lessons in preparation for a deliberate release of biological agents by terrorists. But there is a darker side to the relation between naturally emerging infections and bioterrorism. Whereas clinicians and policy makers view diseases like SARS as public-health threats, terrorists could see them as weapons of opportunity.

SARS-associated coronavirus has several features that could be uniquely attractive to those seeking a biological weapon (table ). The SARS pathogen is highly contagious. Of the healthcare workers who had unprotected exposure to the initial SARS cases in Asia, more than 50% became ill.⁵ If SARS was released within a susceptible population, it could proliferate extensively before containment measures were implemented. A well-defined geographical distribution of cases was integral to the identification of suspect SARS cases in the 2002–03 outbreak. Wider distribution could delay identification, making it difficult to control the spread of infection.

Table.

Features of SARS relevant to biological weapons

	SARS	Smallpox	Influenza	Ebola
Communicability	High	High	High	Intermediate
Lethality	>50%	30%	<5%	>75%
Treatment	No known therapy	Supportive care	Antiviral agents	Supportive care
Prevention	No vaccine	Vaccine available	Vaccine available	No vaccine
Availability	Likely available	Restricted	Commonly available	Very limited
Detectability	No rapid diagnosis	No rapid diagnosis	Rapid assay available	No rapid diagnosis

Lethality also makes SARS coronavirus a viable bioterrorism agent. The mortality rate from SARS during the 2002–03 epidemic exceeded 40% in elderly and debilitated people.⁶ SARS also killed people who were young and otherwise healthy. The demographic profile of healthcare workers who died of SARS is comparable to that of military personnel. Therefore, SARS coronavirus has the potential to be employed as a weapon targeted at military units. Moreover the prolonged convalescence of those who survive SARS infection would further strain the resources of the nation or military units attacked.⁷

Unlike smallpox, access to SARS coronavirus is not heavily restricted; it is conceivable that the virus could be obtained from the wild. Many deaths from SARS during the 2002–03 epidemic were in parts of the world where security of the remains is not guaranteed. As a result, several nations have access to specimens from which large quantities of SARS coronavirus could be cultivated. Furthermore, the virus could be obtained from the animal species that seem to be its natural reservoirs.

The most alarming feature of SARS coronavirus as a potential bioweapon is perhaps the difficulty in detecting an attack. coinciding with the influenza season may not be detected until after widespread transmission has taken place. Detection of the epidemic of 2002–03 was helped by a limited geographical distribution, which was the result of the outward spread of the virus from a single focus. By contrast, a deliberate attack would likely be designed to spread the virus and would result in proliferation of new cases over a wide area. As such, the opportunity to contain the epidemic and to follow a forensic trail to identify those responsible would likely be lost.

The resources devoted to understanding SARS and preventing another natural epidemic have been generous and seemingly effective. Preventing a deliberate epidemic will be more difficult. In addition to developing improved treatments and containment strategies for SARS, the factors that make SARS coronavirus a potential bioweapon must be addressed.

Access to specimens from which SARS coronavirus and other emerging pathogens can be isolated and made into weapons should be limited. Proper documentation and a secure chain of custody, lacking from most healthcare settings and absent from many preparedness plans, must be strengthened and applied to clinical samples, sick patients, and the remains of those who have died. Such measures will complement efforts to reduce the likelihood of laboratory accidents involving SARS coronavirus.⁸ It may also be time to reconsider current standards for sharing technical information about emerging pathogens. Although dissemination of the genetic sequence of SARS coronavirus could advance research on countermeasures, it could also help those who intend harm. Greater accountability for access to such information is needed. The scientific and clinical communities should direct the structure and application of such regulations.

Current systems intended to detect the onset of naturally emerging infections may be of limited use for detecting the deliberate spread of SARS coronavirus and similar agents, and must be strengthened-for example, automated detectors of airborne pathogens may not identify human carriers intentionally infected with SARS coronavirus. Likewise, syndromic surveillance could miss the clues that an attack with SARS coronavirus is underway, especially if surveillance is limited in scope or not deployed near the location of the attack.⁹ Notably, the US anthrax attack was not recognised through elaborate sensors or surveillance networks but through the meticulous attention of a single clinician. Wide distribution of a validated, rapid diagnostic assay for the detection of SARS coronavirus in patients with a suspicious clinical syndrome will be a critical aid to detecting an attack.