As health officials scramble to explain how two nurses in Dallas became infected with Ebola, psychologists are increasingly concerned about another kind of contagion, whose symptoms range from heightened anxiety to avoidance of public places to full-blown hysteria.

So far, emergency rooms have not been overwhelmed with people afraid that they have caught the Ebola virus, and no one is hiding in the basement and hoarding food. But there is little doubt that the events of the past week have left the public increasingly worried, particularly the admission by Dr. Thomas R. Frieden, director the of the Centers for Disease Control and Prevention, that the initial response to the first Ebola case diagnosed in the United States was inadequate.

Experts who study public psychology say the next few weeks will be crucial to containing mounting anxiety. “Officials will have to be very, very careful,” said Paul Slovic, president of Decision Research, a nonprofit that studies public health and perceptions of threat. “Once trust starts to erode, the next time they tell you not to worry — you worry.”

The risk of Ebola infection remains vanishingly small in this country. The virus is not airborne, not able to travel in the way that, say, measles or the SARS virus can. Close contact with a patient is required for transmission. Just one death from Ebola has occurred here, and medical care is light-years from that available in West Africa, where more than 4,400 people have died in the latest outbreak.

By contrast, in some years, the flu kills more than 30,000 people in the United States. Yet this excites little anxiety: Millions of people who could benefit from a flu shot do not get one.

“We’re familiar with the flu, we’ve had it and gotten better — we feel we know that threat,” Dr. Slovic said.

Experts said the most recent precedent of the Ebola risk, psychologically speaking, is the anthrax scare that followed the Sept. 11 attacks. In the weeks after an unknown assailant sent deadly envelopes with powdered anthrax spores to public officials, people across the country were seized by anxiety.

Some duct-taped windows and stayed away from work. In pockets of the country — in Tennessee, Maryland and Washington — people reported physical symptoms like headaches, nausea and faintness. Ultimately they were determined to be the result of hysteria.

“I was in college then, and I remember they evacuated the business school building because someone saw white powder in the cafeteria,” said Andrew Noymer, a sociologist at the University of California, Irvine. The powder turned out to be artificial sweetener.

Ebola has arrived at a different cultural moment from the anthrax attacks. In 2001, fears of imminent terrorism were all too real. Still, perception of risk is far from a strictly rational calculation.

Psychologists have known for years that people judge risk based on a sophisticated balance of emotion and deduction. Often the former trumps the latter.

Instinctual reactions are quick and automatic, useful in times when the facts are not known or there is not enough time to process what little is known. Analytical reasoning is much slower and much harder; if we relied on analysis alone, decisions about risk would paralyze us.

In everyday life, the mind juggles the two methods of risk assessment. Research into this process, some of it by the Nobel laureate Daniel Kahneman and his research partner Amos Tversky, demonstrates that instinctual biases can alter how people gauge the odds in making a wide variety of presumably rational decisions, from investing money to preparing for disasters.

For example, most people appreciate that a chance of infection of one in a 100 million is near zero. But if a friend says he knows an infected person, then our instinctive risk-assessment system is much more likely to focus on numerator than the denominator. Am I the one in 100 million? Me?

“The system often flips from one extreme to another, from ignoring risks altogether and then overreacting,” said George Loewenstein, a professor of economics and psychology at Carnegie Mellon University.

The Ebola outbreak has many of the elements that could quickly stoke instinctual panic, experts note. It is invisible and deadly, a point graphically communicated in nonstop pictures and videos from Africa. Like SARS, and more recently MERS, Middle Eastern Respiratory Syndrome, and bird flu, it is a strange, exotic threat, and there is little that can be done personally to limit it.

These elements are precisely those that are most likely to cause contagious anxiety, researchers have found.

Add to this the fact that death from Ebola is so gruesome, and people can become fearful very quickly. “It’s the same reason we’re terrified of airplane accidents, because we can’t imagine what those last moments might be like,” Dr. Lowenstein said.

At the moment, health authorities are struggling to retain the public’s trust, a crucial brake on runaway anxiety. The most important factors, Dr. Slovic said, will be competence and fairness: communicating the risks clearly; reporting all cases as quickly as possible; and treating each infection with the maximum level of care.

Officials will be walking a fine line, he said. “This could tip very quickly.”

Written by Benedict Carey for The New York Times ~ October 15, 2014.

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