If the current bird-flu outbreak becomes a pandemic, fear could turn to panic. Experts say whether that happens will probably depend on how honest governments are with the public.
In the flu pandemic of 1918, there was enough panic that society began to disintegrate in some cities, says historian John Barry, author of The Great Influenza.
"Close blood relatives were so frightened that they would not feed a family where people were starving to death," he says.
But Barry says that sort of panic wasn't caused by the flu alone. It came after officials tried to reassure the public by telling half-truths, and even lies.
The surgeon general even tried to convince people that the 1918 virus was no worse than an ordinary influenza.
"The obvious lies led to a breakdown in all trust in authority," Barry says. "People understood very rapidly that this was not ordinary influenza, given the horrific symptoms, given the enormous death toll. Given the fact that people were dying sometimes within 24 hours after the first symptoms."
When people can't trust the government, they turn to other sources of information, including rumors. The result can be extreme behavior.
Barry says that's what happened in Phoenix in 1918.
"Rumors spread that dogs were carrying the disease," he says. "People started killing their pets. And if people didn't have the heart to kill their own pets, their dogs, they gave them to the cops and the cops were killing them.
Of course, it was people spreading the disease, not dogs.
U.S. health officials say such episodes have taught them how important it is to tell the full truth. Health and Human Services Secretary Mike Leavitt has been making a point of describing a potential flu pandemic in graphic terms.
But in some Asian countries, officials have been less forthcoming about bird flu, or the deadly outbreak of SARS.
China offers a good example of what not to do, says Peter Sandman, a risk communications expert in Princeton, N.J.
"The only panic we saw during the SARS outbreaks was in China," Sandman says. "It was as a result of the Chinese government misleading people about the existence of SARS in China, which the Chinese government maintained it was doing in order to prevent panic."
Sandman calls this "panic panic." He says it occurs when the government fears the public can't handle the truth. He says that's a mistake.
"Panic is very rare," he says. "I think a pandemic is likelier to provoke panic than almost any other catastrophe. But even in a pandemic, most of the time, most people don't panic. They get very frightened and very upset and they feel panicky and they cope."
Sandman says U.S. officials have offered some false reassurances about bird flu. For example, they like to remind people that the bird-flu virus has yet to infect any birds in this country. But Sandman says that doesn't make most of us any safer.
It really doesn't matter whether birds in the U.S. get the virus, Sandman says. What matters is whether the virus has begun spreading easily from person to person.
"Unless you're in the poultry industry, your risk is not significantly increased when (the virus) comes to local birds," Sandman says. "The risk of eating chicken is marginally increased, so there is some real change, but very small. The risk of a pandemic doesn't change at all."
Recent efforts to reassure Americans suggest that the Bush Administration hasn't fully learned the lessons of the 1918, says Dr. Jody Lanard, a psychiatrist who is married to Sandman and works with him on bird-flu risk.
"That's why we end up having President Bush on his first major pandemic statement talking about martial law," Lanard says.
She says such talk is a symptom of "panic panic."
Lanard says what the president should be doing is encouraging "the kind of public resilience that we do see after most hurricanes, and that we did see in the World Trade Center."
"They're going to the rare, unusual case of public hysteria and disorder, instead of counting on the public to be the way Americans usually are — highly, highly resilient."
Lanard says officials can tap into that resilience by telling people how they can work together to protect themselves even when things get really bad.