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Last Updated

04 Apr 2003

Source: Wall Street Journal, April 4, 2003


Epidemics Can Take A Variety of Courses

History Offers Clues as to How SARS May Grow -- or Dissipate


When will it end? That is the question haunting anxious travelers, a worried public and vigilant doctors trying to track and outflank the swiftly spreading outbreak of SARS, or severe acute respiratory syndrome.

Will it infect thousands more, burn itself out or return to the animals from whence it came, only to resurface next year with greater fury? Absent a crystal ball, scientists are looking at past flu epidemics and hedging their bets.

Three superepidemics, known as pandemics, of influenza encircled the globe during the 20th century. The first was 1918 Spanish Flu, a scourge that killed over 20 million people world-wide, including 500,000 in the U.S. The 1957 Asian Flu and the 1968 Hong Kong Flu killed 69,800 and 33,800 respectively in the U.S. Flu pandemics happen when the flu virus mutates, swaps genes with another bug inside an infected animal, or jumps from animals to humans, which is what experts believe happened with SARS, although SARS isn't influenza.

Experts also point out that there have been more scares in recent years than actual pandemics. The 1976 Swine Flu Scare, 1977 Russian Flu Scare and 1997 Avian Flu Scare were all feared to be the next pandemic. In the Avian Flu scare in Asia, 18 people were hospitalized, six died and 1.5 million chickens were slaughtered in Hong Kong.

SARS could go either way. "There is a possibility, with good public-health measures, that the epidemic will rapidly die down," says Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health in Bethesda, Md. "However, we may be seeing only the tip of the iceberg."

Because SARS is a new disease, "it is entirely unpredictable as to how this epidemic will evolve," Dr. Fauci adds. SARS is thought by many to be a new member of the coronavirus family that includes the common cold, along with more severe respiratory diseases of pigs and fowl.

"The evolution of an epidemic depends first upon the susceptibility of human hosts: how likely are people to fall ill, how severely do they fall ill, and how long are they infectious?" says Klaus Stohr, project leader of the World Health Organization's Global Influenza Program in Geneva.

One of the many factors that will determine the epidemic's duration and toll is its mode of transmission. Early on, it was thought to require very close contact and inhaled respiratory droplets to spread the disease, but now experts are considering the possibility that lingering fine mists or contaminated objects or areas could spread infection over a greater distance. And no one knows whether people who aren't coughing and sneezing are spreading the disease.

Noting how jet travel has quickly spread SARS, Dr. Stohr says, "If this disease had occurred 100 years ago, it would not have become a global problem in the twinkling of an eye, spreading disease over thousands of miles."

Some doctors have observed that certain patients appear to be supercontagious. And doctors in some places also think that the bug seems to become weaker as it is passed along from person to person. Often, fast-replicating viruses develop genetic mutations that weaken the virus. But, at the Centers for Disease Control and Prevention in Atlanta, Sherif Zaki, chief pathologist, says, "We have no indication it will get weaker. The precedent is for viruses to weaken, but it's still early, so we can't be more definite."

Other reasons could account for what doctors interpret as waning virulence, such as people getting medical help earlier or simply not having as much virus in their system.

"I'm not a believer in waning virulence," says Peter Jahrling, a military virologist who studies smallpox and Ebola with the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Md. Dr. Jahrling predicts the death rate will hold steady at 4% to 5% of total SARS cases.

"A lot of public-health experts are taking this very seriously," he says. "It might fizzle, but flu usually floats around the globe until everyone is either infected or immunized. This bug could be just like it. It probably emerged from animal hosts but that doesn't mean it will recede. It can probably sustain itself in humans just like flu."

U.S. officials stress there is no specific treatment proved to work against SARS, although many drugs are being screened for possible efficacy against the virus.

An important factor in determining how far a bug spreads is how quickly patients can be confined and isolated, Dr. Stohr of the WHO says. From Hong Kong's "holidays camps" to home or hospital isolation, isolating the sick and quarantining the exposed remains the best hedge against pandemic for now.

In a sobering editorial in this week's New England Journal of Medicine, CDC Director Julie L. Gerberding said that while the suspect coronavirus was identified with unprecedented speed, it is too soon to predict either the ultimate scope of the disease, or whether drugs and vaccines can be made fast enough to curtail an extensive global outbreak.

"If we are extremely lucky," she said, "the epidemic will be curtailed, develop a seasonal pattern that will improve prospects for regional curtailment, or evolve more slowly than it has in this early stage. If the virus moves faster than our scientific, communications, and control capacities, we could be in for a long, difficult race."

-- Betsy McKay contributed to this article.