A Primer On SARS

By Michael Barnaby

John Snow removed the handle from a "much frequented" London water pump and ended a terrible cholera outbreak. This single action marked the beginning of the modern epidemiological process. The histories and control of smallpox, polio and numerous other diseases can be told in terms of their epidemiology, and the same method is being employed today in the case of Severe Acute Respiratory Syndrome, or SARS.

Snow, in 1854, showed through diligent, painstaking tracking and documentation that cholera was a contagious disease that could be transmitted through water. In March of 2003 a worldwide collaboration of 11 laboratories in nine nations began the task of identifying the cause of SARS and the route of its transmission.

The known history of SARS appears to have begun in Southern China when on February 21 a doctor who had treated patients in Guangdong Province traveled to the Metropole Hotel in Hong Kong to attend a wedding, staying on the ninth floor. This doctor infected between six and nine other people staying on that floor, at least two of whom have since died, as has the doctor and his brother-in-law (who did not stay at the hotel but dined there). These infected guests were then responsible for secondary clusters of cases in Toronto, Hanoi, Singapore, and further cases at three different Hong Kong hospitals.

Another of the infected guests, an American businessman, then traveled to Hanoi, became ill and infected more than 20 health care workers at the French Hospital in Hanoi. The hospital was closed and the man transferred to Hong Kong, where he died. At least 367 cases have since occurred in Hong Kong, and transmission has been documented from patients to healthcare workers to healthcare workers’ families, and finally into the local school system. The American businessman’s illness sparked the investigation into SARS.

Although the cause of SARS is not known at this time, two viruses have consistently been isolated from many patients, even in differing parts of the world. But "It is not normal that one disease is caused by two viruses," Dr. Klaus Stohr, a World Health Organization (WHO) virologist and epidemiologist, told a press conference on March 25. Through the epidemiological process, he was able to report by March 27 that "Data from many network laboratories indicate that a coronavirus is the primary cause of the disease." The Centers for Disease Control and Prevention (CDC) have also produced strong evidence implicating a coronavirus as the causitive agent in SARS.

As of the end of March 2003, no treatment beyond good intensive and supportive care has been consistently shown to help people with SARS, which has an estimated four per cent death rate. But through the field of epidemiology, the mysteries of this new disease are patiently, methodically and rapidly being solved.