How dangerous is SARS?

Health and medicine explained.
April 3 2003 3:42 PM

Travel Bug

Should you cancel your trip to the Orient because of SARS?

You've booked a business-class ticket on Cathay Pacific to Hanoi and reserved a room at the city's historic Sofitel Metropole—a French Colonial treasure. Your renewed passport offers a dozen unstamped pages for the other Asian ports of call on your still-evolving itinerary. You dust off an old money belt, purchase travel insurance, and buy an electrical adapter plug with ridiculously fat prongs. But then you learn that a mysterious new pestilence with a frightening name, severe acute respiratory syndrome, has hit Hanoi.

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Should you stay or should you go? Depends on whom you ask.

The two public health outfits leading the efforts to understand and control this outbreak of SARS offer conflicting travel advice. The U.S. Centers for Disease Control and Prevention first issued a travel advisory on March 13, which it updated on the 28th. The CDC cautiously counsels against "elective or nonessential travel" to anywhere in mainland China, Hong Kong, Singapore, or Hanoi, Vietnam. Those people "may wish to postpone their trips." Even though Health Canada had reported 58 "probable" and 93 "suspect" cases by April 1, the CDC says the epidemiology there "is significantly different with regards to community transmission"—meaning the Canadians have aggressively controlled the spread—and does not warrant a travel advisory. The CDC advisory does not say whether it mainly intends to protect travelers or limit global spread.

The World Health Organization, in contrast, kept mum about travel restrictions until April 2, when it issued a much more circumscribed advisory than the ones from the CDC. The WHO says people should "consider postponing all but essential travel" to Hong Kong and Guangdong Province, China. WHO based its advisory on the aggressive spread of the disease in Hong Kong, which has 708 cases, nearly one-third of the world's total. The WHO, which promises to reassess its recommendation daily, explicitly states that it hopes the advisory will limit the spread of SARS.

It's something of a mug's game to assess risk here: SARS just emerged, and scientists don't definitively know its cause, how it transmits, how widely it has spread, how to prevent it, or, most soberingly, how to effectively treat it. Risk also, to a large degree, is in the eye of the beholder. And the advisers here cook up their recommendations with one part public health, one part politics: Putting a skull-and-crossbones sticker on a locale has serious economic impacts and also strains the delicate relationships that the CDC and WHO have with many governments. But some objective facts do exist that offer extra guidance and help square the differences between the WHO and CDC advice.

Hanoi at the moment looks fairly tame. It only had 58 cases as of April 2, and all seemed linked to one Chinese doctor from Guangdong who stayed at the decidedly unhistoric—but now infamous—Metropole Hotel in Hong Kong. (The CDC's March 28 Morbidity and Mortality Weekly Report chronicles how the disease spread from the Guangdong doctor to 13 people in the hotel, and then on to Vietnam, Singapore, Thailand, Canada, Germany, Ireland, and the United States. See Figure 1 for a real eye-popper.) Similarly, Singapore only has 95 cases, many of which link directly to the Guangdong doctor. Health-care workers account for roughly half of the total cases in Singapore and Hanoi, highlighting that the greatest risk exists in hospitals there.

Outside of Guangdong, the hardest hit region in the world with 1,153 cases, China has only reported another 37 cases to date. So mainland China looks relatively safe. But given that government's less-than-forthcoming behavior about this outbreak, expect more surprises from China.

Hong Kong and Guangdong obviously present the highest risks. Then again, keep in mind that nearly 7 million people live in Hong Kong and 86 million live in Guangdong Province. When compared to the total number of reported cases in these regions, that means the disease has only spread to roughly .00002 percent of the residents.

Bottom-line advice: Treat CDC and WHO advisories like weather reports. If the storm gathers force in a region where you're heading, reschedule. As a rule of thumb, if no new SARS surfaces in a region for more than 22 days—twice the maximum length of time that scientists estimate a person remains infectious—the outbreak has petered out, and the sun has returned.

Jon Cohen writes for Science magazine. Follow him on Twitter.

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