So far the swine flu has frightened far more people than it has infected, but fear of a disease can be just as potent as the sickness itself. Outbreaks of plague in medieval Europe led to the murder or exile of Jews who had nothing to do with its spread. In the 20th century, the specter of contagion was used to turn impoverished immigrants away from Ellis Island, demonize gay men and discourage women from getting jobs and even wearing shorter skirts. “So often epidemics end up as campaigns to capitalize on people’s fears or spread prejudice or encourage one or another kind of injustice,” says Philip Alcabes, a public health professor at Hunter College of the City University of New York and the author of a new book, “Dread: How Fear and Fantasy Have Fueled Epidemics From the Black Death to Avian Flu.”

To understand the history of epidemics as cultural forces, Alcabes, an epidemiologist by training and an AIDS expert, delved into both scientific literature and works of fiction ranging from Albert Camus’s “The Plague” to Michael Crichton’s “The Andromeda Strain.” The story that a society tells itself about a disease, he discovered, is just as important as the disease’s actual mechanism. Often these narratives reveal a cultural unease that looms larger than the sickness – sexual anxiety, for instance, or suspicion of foreigners.

Though in recent years America has largely been spared from killer epidemics, the terminology has spread to cover a variety of non-contagious phenomena. The obesity epidemic. The autism epidemic. The drunk driving epidemic. Alcabes shared his thoughts on the swine flu “epidemic,” and on the history and psychology of that fearsome word:

What is an epidemic? And how is it different from a plain old disease?

If you’re an epidemiologist there’s a very simple answer – an epidemic is more than the expected number of cases of a particular disease in a given place and time. That’s easy. But that doesn’t describe what epidemics mean to people. A little more expansive definition is that an epidemic is a disaster of some kind, or, to get still more expansive, an epidemic is a perceived disaster. I write at the end of the book about autism, and autism as an epidemic. There is much more autism among children today than there was a generation or a couple of generations ago. On the other hand, the preponderance of evidence does not suggest that there’s something happening that’s making more kids be born with autism. The increase in autism seems to happen as a combination of expanding diagnosis and changing diagnostic patterns, plus better awareness of the problem and more awareness of what can be done for autistic kids. So there you could say what’s going on is perceptual.

Is swine flu an epidemic?

Yes, sure. Why? Because people are talking about it as an epidemic. And an epidemiologist would say that, since we have never seen cases of this strain before, as soon as we have seen some cases it’s an epidemic.

Can we learn anything about what’s going on now from the swine flu “epidemic” of 1976?

I believe there is much to be learned from what happened in 1976. Health officials were too quick to assume that we were going to see a repeat of 1918, the so-called Spanish flu epidemic (which killed millions). In 1976, officials pulled the switch too soon and called for mass vaccinations against this particular flu strain. And they did it because they had been convinced by some bad history that there was a great likelihood of a very severe and widespread flu epidemic at that time. As a result of this mass vaccination program, some people died. They died from Guillian-Barre Syndrome (an immune system disorder) and no flu was prevented because there was no outbreak. There was the usual outbreak of garden-variety seasonal influenza but not of the new strain. For me there’s a lesson there. I think responding to flu requires balancing sound public health measures against the need to have some foresight. What happened there was the sound measures were outstripped by the desire to predict in advance of the facts.

People used to see epidemics as the work of God?

In many ancient cultures, it was assumed what we now call epidemics were random acts of God or gods that couldn’t be explained. In fact, a kind of philosophical advance that the ancient Hebrews brought was that disaster happened because God got angry (with people). These were real attempts to explain what happened on the basis of people’s actions. The leading example is the ten plagues in Exodus. God smites the Egyptians with these plagues because they won’t let the Hebrews go. The idea was that when there are natural disasters it’s not a random eruption of the spirit world but a predictable response by an angry deity.

You say the Black Death was the archetypal epidemic.

We think of epidemics in the pattern of the Black Death. It comes suddenly, without warning, and causes great harm. And then it goes away. There are certain really terrible disease disasters that we don’t call epidemics. Worldwide there are about 1.8 million deaths per year from tuberculosis but we don’t say there’s a tuberculosis epidemic. We don’t talk about that as an epidemic because TB does the same thing year in and year out. There’s something about the sameness of that, the predictability of it, that makes us not consider it an epidemic.

How did medieval epidemics help strengthen communities?

The era of the plague starts in Europe in the mid-1300s and goes to about the year 1700. One of the things that’s remarkable is that at the same time as there were these florid and violent responses that I write about -- the burning of the Jews and hounding people out of their homes and exiling them from the land -- there were also very cogent and thoughtful communitarian responses, like quarantine. Communities decided to protect themselves by preventing goods from coming in or people from coming in, which in essence were the beginnings of public health intervention.

In the 20th century, how did epidemics impact the status of marginalized ethnic groups like Jews in Europe and Irish immigrants and blacks in America?

One of the themes that threads through the history of thinking about epidemics is this idea of fear or suspicion of foreigners or outsiders, fears about people who don’t seem to fit in. The Black Death example is the Christian townspeople in Western Europe who seized on Jews as the cause. Now they basically knew Jews weren’t the cause of the plague, but in many places nonetheless they either ran the Jews out of town or beat them or burned them to death. It was an expression of some unconscious, or not-so-unconscious, fear that I think was really about the stability of society. Fortunately we don’t see so much burning at the stake anymore when there are epidemics. But there’s still an impulse to fix on foreigners and outsiders as being suspect, as being somehow responsible. With cholera in the mid- 19th century, the suspects were Irish immigrants. There was an outbreak of plague in San Francisco in 1900 that started in Chinatown. The plans for what to do about the plague were tied up with anti-immigrant sentiments, which focused on Chinese-Americans but also included Japanese-Americans.

How did dread of epidemics influence women’s place in society?

There are scholarly papers in peer-reviewed medical journals that attribute tuberculosis (in the 1920s) to the new trend of young women’s independence. Instead of staying home and finding a husband, they were going out, getting jobs, and particularly wearing abbreviated clothing. They go out, catch a chill and one thing leads to another, the thinking went. Was there real science behind this? Yes and no. But it really reflected a set of prejudices about women. You see that set of prejudices more generally in the context of sexually transmitted diseases. There’s a general implication that sexual women are dangerous in the history of disease control in America.

What fears did the AIDS epidemic reveal?

AIDS touched on a really essential tension that had to do with modernity or the nature of modern life toward the last quarter of 20th century. The public health profession was feeling like contagion had been conquered, or could be. In the 1970s small pox was eradicated, polio vaccines had diminished what had been a terrible scourge among children, there was vaccination for measles. It was a hopeful moment. At the same time that there was great faith in the advances of modernity, there was a feeling that maybe bad things were going to happen (because of modernity). That’s a persistent theme in western history, that something we’re doing, something that our parents or our grandparents didn’t do having to do with piety or sex or diet, somehow means we’ll “reap the whirlwind.” Then AIDS comes, and people talk about homosexual men like they're getting their comeuppance. Jerry Falwell even used that term about gay men “reaping the whirlwind.” As if something about the sexual revolution, the post-Stonewall moment, when people were able to come out as gay, had threatened society and society was now being punished. The response to AIDS was fraught with all sorts of ideas about what society was like, and a lot of that was about sex and sexuality, but more generally it was about the sexual revolution, the idea of tolerance of homosexuality, which was still a pretty new thing in those days. And it allowed people to talk about sex.

Can the post-9/11 anthrax “epidemic” be seen as a social coping mechanism?

Living in New York in the fall of 2001, I was really struck by a contrast of (reactions). On the one hand, the World Trade Center had fallen down, 2,700 fellow New Yorkers had just died, but the mood in the city was this kind of “keep on keeping on” circumspection. A month afterward there was the postal anthrax event, and the response to that was such a dramatic contrast. There were five deaths, and that’s sad and terrible for the families of the people who died – but that’s five, not 2,700. Yet in response to anthrax, people would come up to me and say “I’m ironing my mail” or “I’m not opening my mail at all.” Buildings got evacuated whenever somebody saw some white powder. I mean, it was nutty. You would have thought there would have been a nutty response to two iconic towers getting knocked down by planes, which seemed like a science fiction scenario, a horror story scenario. And yet the craziness was in response to anthrax.

Why don’t you think we should bother planning a great deal for the next plague?

We should plan very carefully for the things we know about. For instance, it seems reasonable that if you don’t inspect food supplies for contamination, some food will be contaminated and there will be outbreaks of salmonellosis. That’s the planning I would like to see be done. What concerns me more is the kind of planning that “this might happen” and “it might lead to that” and “it might lead to a third thing” -- scenarios that seem like a stretch. It's kind of like speculation times speculation. We need more real public health planning and less “preparedness.”