As the common cold and influenza season settles in, people are waiting, watching, and wondering: Will SARS be back?
Will that new form of pneumonia join a rogue's gallery of other seasonal viral diseases that make the chilly months a danger zone for millions of people?
Severe Acute Respiratory Syndrome (SARS) began its nine-month rampage last November almost unnoticed, with outbreaks of pneumonia in southern China. Before it was over, SARS became an international sensation. It sickened at least 8,500 people, killed more than 800, closed down cities, and caused billions of dollars in economic damage.
The World Health Organization (WHO) on July 5 declared that SARS had been “controlled.” The WHO chose that word carefully, avoiding any suggestion that SARS had been “eradicated,” which means eliminated as a disease threat in the future.
SARS's debut with cold and flu season, and its fade-out as warmer weather returned, makes some experts believe that the virus is waiting just offstage for Act 2 of a long run.
The Journal of Epidemology and Community Health asked nine international infectious disease experts to discuss the chances of another SARS epidemic. Two felt it would not return, three thought it would, and four weren't sure.
Among the factors arguing for a return, they said, is the seasonal nature of SARS's family of viruses. SARS belongs to a group called coronaviruses, which includes the common cold virus and other respiratory disease viruses which peak during cold weather.
People crowd together indoors during the chilly months, making it easy for viruses to spread from person to person. That close contact may be one reason cold and flu season runs from autumn to spring.
Temperature and humidity may be others. Some coronaviruses spread best in warm tem peratures and low humidity - conditions often found during winter in homes, offices, schools, and other centrally heated buildings.
The SARS virus likes temperatures in the 64 to 72 degrees Fahrenheit range. Scientists think that helps explain why SARS faded faster in poor rural areas of China than Toronto, Hong Kong, and Singapore. Indoor heating in Toronto, and air conditioning in Hong Kong and Singapore, kept temperatures and humidity ideal for SARS to spread.
Experts suspect that the changing seasons had a bigger role in SARS's exit last spring and summer than anyone realizes.
Other factors bolster concerns about a possible SARS return.
Scientists suspect that the SARS epidemic began when a virus that lives in civet cats and other animals infected people. Civet cats and other exotic game are being sold again in southern China's food markets, after a short ban.
Human “carriers,” people who are infected but develop no serious symptoms, may be another reservoir of SARS virus that could trigger a second epidemic.
Public health and infectious disease specialists also are waiting, watching, and wondering, with controls plans set to launch if a second epidemic breaks out. That preparation may mean a milder outbreak.