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U.S. looks at 'social distancing' response to pandemic

From the March ACP Observer, copyright 2007 by the American College of Physicians.

By Stacey Butterfield

The threat of avian influenza has made the once-routine annual preparation for the U.S. flu season a subject worthy of primetime news coverage. Federal guidelines issued Feb. 1 fueled the coverage with recommendations of canceling public gatherings, closing schools and staggering working hours to reduce crowds on public transportation. The Occupational Safety and Health Administration chimed in Feb. 6 with advice to employers to prepare for 40% absenteeism and request they not penalize workers who chose to stay home to care for relatives or prevent spreading the infection.

A 2006 survey found that 94% of Americans are willing to stay home from work to stop the spread of a pandemic influenza virus. Yet, more than one-quarter of the population believe they would lose a job or business if they had to stay home for seven to 10 days. The survey, conducted by the Harvard School of Public Health, raises questions about how the U.S. can best prepare to deal with a flu epidemic.

At the Centers for Disease Control and Prevention, understanding the way people and viruses would behave in a real-life pandemic situation is a major priority. Anthony A. Marfin, MD, is the acting deputy director of the division of global migration and quarantine at the CDC. Dr. Marfin and other researchers have been using mathematical models to understand, and then develop techniques to slow or halt, the spread of influenza.

He spoke with ACP Observer about his work on disease spread in general and the issue of avian flu specifically.

Q: How do you predict the spread of a pandemic flu?

A: There's been a great deal of emphasis on the modeling. There are four or five different groups that all work with certain planning assumptions—measures of transmissibility of a virus and measures of the incubation period between infection and illness.

Then they make assumptions about the way that the virus will be expected to move from its origin, and how it spreads throughout the world. Those are based on models about how people move in the world.

Then they run simulations. They can model what the epidemic would look like. In most cases, they are working in what we would call a severe pandemic, a pandemic that looks more like 1918 or worse. There are assumptions about mortality and the number of people who will become ill after infection—epidemiologic factors that we've been collecting about flu for 70 or 80 years.

The second set of models is to put in various interventions—for example, wearing a surgical mask—and an estimate of the success of that intervention—how many people would wear their masks. They start modeling all those outcomes and look at changes in the projected epidemic curve for the United States.

Q: Can you use the pattern of past disease outbreaks to predict future infection?

A: It's very difficult to talk about, "Well, why don't we go to the scientific database and ask what's effective?" Every disease is different.

These are flu models. The epidemiologic factors are different for each disease because certain diseases are more transmissible or result in a greater attack rate.

In this century, we've only had three flu pandemics. It's hard to have a database created around that. The three pandemics were very different. We had a very severe one in 1918. We had a moderately severe one in 1957. We had a milder one in 1968. It's difficult to build a database in all the situations.

Q: How is the decision made to begin quarantine or isolation?

A: Right now in the U.S., we have a list of nine quarantinable diseases. The most recent addition from a couple of years ago was any influenza with pandemic potential. We have been designated to be on the watch out for any of those diseases entering the United States.

If we identified someone who was coming into the U.S. with one of those diseases, we would consider whether isolation would be of benefit to them, because they are ill and maybe in need of medical care, or of benefit to society.

Quarantine becomes a little more difficult, because you're talking about people who were exposed but not yet ill. There's always a question of whether or not they are infected. Those decisions are very often made by epidemiologic data collected overseas.

Probably the best example of that is the 1995 plague outbreak in India. When people were coming from India, we had to ask ourselves every time whether this person should go into isolation or quarantine.

Q: Besides pharmaceutical interventions, what actions could be taken to slow the spread of a pandemic disease?

A: Social distancing includes measures that reduce the number of personal interactions that a potentially infected person has with a well person. We talk about the cancellation of large public gatherings. We talk about ways to minimize exposure in the workplace, at markets and churches, on public transit.

Probably the greatest social distancing measure that we have is telling ill people to stay home.

There are some common sense things here. We would always encourage a solid, well-thought-out work leave policy where ill people can stay home. An additional piece is a work leave policy that allows people to take care of ill people at home or to watch children.

Other social distancing would be to encourage telecommuting. A workplace would have to have a continuity of operations plan which seeks to minimize the economic impact on the business while still trying to minimize the workplace as a site of transmission.

Then there is the one that tends to get a lot of discussion. It is pretty well accepted that kids play an important part in terms of transmission in any society. School closures must be considered and discussed. It's not just school closure. Some people use the term 'preventive sequestration of children and teens.' It's not only the closure of schools but also preventing reaggregation at places like malls.

Q: What changes would need to be made in the health care system?

A: There have been lots of discussions about setting up hotlines with health care systems in which triage is done by telephone rather than having people aggregate in a physician's office. That's seen as an important piece.

Rather than bringing together a lot of ill people, some with other types of illness than flu, in a doctor's office and having the doctor's office being a site of transmission, we talk about telephone triage to identify those people who must be seen because they are severely ill, and those who are mildly ill or concerned that they've been exposed.

We can come up with ways to treat those people so that they don't aggregate in doctor's offices or emergency rooms.

Q: How would these strategies apply to an avian influenza pandemic?

A: You hear people talk about avian influenza and you hear people talk about pandemic influenza. To the uninitiated, those are one of the same. A lot of us look at it somewhat differently.

H5N1 is the one we talk about because we do see that causing human infections more frequently than some of the other avian influenzas that are currently in the world. The virus that we have now is not the one that we're preparing for. Yes, it causes human illness but if you think about all the potential human-poultry interactions that go on in this world every day, it's extremely infrequent.

Yes, it does cause death. It seems that this particular type of virus is very virulent in human beings and has a high mortality. We don't use the term pandemic influenza for the current H5N1 that's occurring worldwide.

Q: At what point would avian flu be classified as a pandemic?

A: The pandemic strain is the one that can be transmitted from a human to a human to a human in a sustained fashion. That's the strain that we're worried about. That's the strain that we have worldwide surveillance looking for.

It doesn't have anything to do with the number of infections. We know that influenza moves rapidly throughout the world, so we would say the new emerging strain is going to rapidly enter the human population and then become one of the predominant strains.

But influenza's not the only pandemic. If you look at plague literature, we have times when it has caused lots of disease, such as the Black Death in Europe in the Middle Ages. And then we have times like we have now where there is a strain of plague that has moved throughout the world but it has not caused a lot of human disease at this time.

The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP.

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