Prepare for the return of the deadly SARS virus

Marc Lipsitch, Professor of Epidemiology, Harvard School of Public Health, Project Syndicate

Every winter, millions of people around the world suffering from flu-like illnesses visit their doctor. Some patients actually are infected with flu; others have colds or other respiratory infections, many of which also peak in the winter. This coming flu season there will be a new twist: Physicians will have to be aware that hidden among these patients could be a small number with SARS, a respiratory disease that is also likely to be seasonal and whose early symptoms are almost indistinguishable from those of the flu.

If even a few SARS cases are present among the millions of flu-like cases that will appear this autumn, it will be critical to identify and isolate them to prevent a repeat of the epidemic that scourged China earlier this year. But among the vast number of flu and other cases, finding these cases will be difficult. Paradoxically, the best way for health authorities to prepare for a possible return of SARS this winter is to make special efforts to reduce the spread of flu and speed its diagnosis.

This may be a tough sell politically. Unfortunately, if predictably, the remarkable success of efforts around the world to control the transmission of SARS -- particularly in Taiwan and mainland China -- has led some to question whether the threat of SARS was "overblown." But the very reason we have the luxury to ask such questions is that the spread of the infection was contained by exceedingly stringent measures.

Rapid and effective isolation of infected cases, together with efficient tracing and monitoring of the contacts made by those infected with SARS, allowed public health officials in Hong Kong, Toronto, Singapore, and Vietnam to contain the epidemic. Screening travelers from affected regions may have prevented significant epidemics elsewhere. Health officials around the world should maintain their vigilance and prepare for the possibility that renewed control efforts will be required if SARS resurges.

Indeed, the experience with SARS in Toronto, where cases escaped detection and led to a second outbreak, stands as a warning against excessive optimism about the apparent control of the larger and more geographically dispersed outbreaks in Taiwan and mainland China. These epidemics may, in fact, be eliminated entirely in coming months. But it is at least as likely that some transmission will persist, or that the virus will be reintroduced into human populations from animals.

Like other respiratory infections, SARS may be easier to contract, more severe, or both, during winter. Continued surveillance and infection control measures will be required to ensure that the accomplishments of the last few months are not undone by a few undetected cases that touch off new SARS hot spots.

Surveillance will not be easy. SARS is difficult to diagnose definitively, and during flu season, it will be much easier to miss a case of SARS. With current tests, it is impossible to verify that a patient has been infected with SARS until several weeks after symptoms begin.

Experience around the world shows that SARS cases must be isolated within a few days of the onset of symptoms in order to control the spread of the virus. The dilemma is that playing it safe -- by treating every flu-like illness with the precautions appropriate for SARS -- would present an enormous logistical, operational and financial burden to health care systems. But to ignore the possibility that some such patients are SARS cases risks the start of new outbreaks.

We don't have vaccines or rapid tests for SARS, but we do have them for flu. We need to use them. Influenza vaccine supplies should be increased so that more individuals are inoculated. Extra efforts should be made to encourage more people to get a flu shot, including those outside the traditional "target" groups, such as elderly people and health care workers.

By preventing influenza, these vaccines reduce the number of individuals to be evaluated for SARS. Kits for rapid diagnosis of influenza infection already exist. If more physicians had routine access to these kits, they could tell on the spot whether a patient had influenza and eliminate the need to treat him or her as a possible SARS patient.

Even assuming the best-case scenario -- that SARS is eliminated by the end of this year -- increased flu vaccination and better availability of diagnostics will benefit millions of people worldwide. According to the World Health Organization, as many as half a million people die each year from influenza. Many more are hospitalized with severe illness. Wider vaccination will protect people from infection and block the spread of the virus. Broader use of rapid diagnostics will permit more effective treatment for flu cases at risk of developing serious complications.

If SARS is brought under control worldwide in the next few months, public health authorities will have achieved a great triumph. Successful containment of SARS might mark the first time in history that person-to-person, respiratory transmission of a major pathogen has been halted globally without the use of antibiotics or a vaccine.

But we would be foolish to think we have seen the last of SARS, and it will take time for scientists to develop diagnostics, treatments, and vaccines. In the meantime, we should intensify the fight against an older nemesis, influenza, both for its own sake and as a way to prepare for the return of SARS.