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April 10, 2021  

Dr. Stephen Zinner

Dr. Stephen Zinner: An Infectious Disease Expert Discusses SARS

July 23, 2003

Stephen H. Zinner, M.D., is recognized worldwide as an expert on infectious diseases. He is chair of the Department of Medicine at Mount Auburn Hospital in Cambridge, Mass., and a professor at Harvard Medical School. Dr. Zinner is a member of the Advisory Board of the International Antimicrobial Therapy Cooperative Group of the European Organization for Research and Treatment of Cancer, and has published widely on epidemiology. He is a Fellow of the American College of Epidemiology, the American College of Physicians, and the Infectious Diseases Society of America.

In an interview with Body1, Dr. Zinner summarized the latest findings about SARS (severe acute respiratory syndrome) and answered questions about the nature, spread, and treatment of this life-threatening disease.

Body1: In your experience, how do you characterize the current threat of infectious diseases and the state of infectious disease control?

Dr. Zinner: No public is ever going to be free of infectious diseases. The challenge is to stay ahead of the curve with the development of better antibiotics and, more importantly, the appropriate use of the antibiotics that we have. We can still treat and cure most bacterial infections, and we also have new drugs, either existing or emerging, for viral and fungal infections.

We have not eradicated infectious diseases from the face of the earth or from this country, nor will we ever do so in all likelihood. A case in point is the increasing emergence of antibiotic-resistant bacteria in our own communities, our own most affluent communities where antibiotics use has been excessive over the last several decades.

This is our most vulnerable point, in my opinion. We are now seeing the emergence of common bacteria that are resistant to many, perhaps most, antibiotics. These bacteria are the ones that cause common infections. I believe the threat of losing the battle against antibiotic-resistant bacteria probably is as great, if not greater, than the introduction of one or two cases of a new infection in a community, the emergence of another new disease like Legionnaires' disease, West Nile virus, or SARS.

We do not yet know every detail of how SARS virus emerged. SARS virus appears to be a new variant of coronavirus, a common group of viruses that includes the cause of the common cold. SARS virus is a more potent cause of illness than the other coronaviruses.

Body1: Is there a pattern in the spread of SARS?

Dr. Zinner: As a rule, whenever and however a new microbiological agent emerges such as SARS virus, there is obviously a huge pool of susceptible persons to begin with.

West Nile virus is a perfect example. When it first entered this country in 1999, nobody had encountered it before, so the entire population was susceptible. This particular virus, when it causes infection, only produces symptoms in perhaps 15 to 20 percent of the people who are infected by it. The next time, the majority of infected people who had no symptoms, who never even knew that they were infected, are no longer susceptible. They've encountered the virus, and they've contained it with their natural immune system.

So the next time that virus comes around, it won't have a 100 percent susceptible population, but only a smaller pool. And that pool of susceptible people will be fewer and fewer in the third cycle, the fourth, and so on.

So one can predict that when a new agent enters the community, the most susceptible people - usually the very young and the very old - are most likely to have the illness associated with it. And that over the course of time the number of susceptible people will be reduced. And the problem will become contained. That is probably what is happening in the case of West Nile virus.

SARS is new, so we do not have that historical view that would allow us to state that the disease is following one or another known or typical pattern. It is too early to tell. But most likely it will fit a known pattern. The evidence that I cite is that in those countries like Singapore that have the ability to monitor and control, in other words to appropriately isolate and quarantine, the infected population, the incidence of cases is going down, if not gone. In a place like China, where we don't have the same degree of confidence in the public health system that we do in Singapore, Vietnam, Taiwan, Canada or the US, we really don't know.

In this country, we are favored with a superb national infrastructure. The federal Centers for Disease Control is a highly reactive and responsive agency. It instantly pounces upon the first evidence of any kind of infectious disease emergency or problem. However, the public health infrastructure in each state has been consistently threatened by budgetary constraints over the past two decades. Relying on existing antibiotics, state public health systems had let their guard down, assuming that infectious disease problems were under control and therefore cutting back on resources.

Body1: Looking specifically at SARS, alarmingly, recent news reports tell us that SARS fatalities are being underestimated. Chinese estimates were originally 4 percent and are now revised to 15 percent. In other words, the virulence is three times the initial estimate. Are we going to see this percentage continue to climb?

Dr. Zinner: The problem of getting accurate data in China is obvious. They do not have the infrastructures that we do here. It's probable that the mortality rates are highest in the extremes of age - the very young and very old - and in people who are ill. In the instance of a serious untreatable disease like SARS, it would not be surprising to see a range of fatality rates from one to around 15 percent.

When you say the "virulence" is three times the initial estimate, I don't think that is true. I think it's the epidemiology and the accuracy or inaccuracy of reporting that accounts for that variation. I don't think that the fatality rates - the percentage who die - are likely to go up much more. It will likely settle somewhere between those extremes of 4 to 15 percent, with the highest rates belonging to the extremes of age and those with underlying diseases.

Body1: What is it about SARS that has caused it to be so seriously underestimated?

Dr. Zinner: The answer lies not with the virus but with the infrastructure of the public health system in the place where SARS was first discovered. One could probably argue that, had SARS appeared in a more developed and open society having an adequate and well-used public-health infrastructure, it might have been contained in that place of origin and never spread. However, we do not know that for certain. It is speculation.

Whenever a new agent or illness emerges, it has to be recognized and understood, and the means of controlling it have to be identified and mobilized. All this takes some time under the best of circumstances. In an arena where we do not have access to the information, it's really hard to make appropriate estimates. That really does not surprise me.

Body1: Is SARS now considered to be an entire class or cluster of diseases? Is the virus constantly mutating, like flu does?

Dr. Zinner: The basic virology of influenza ("flu") virus is very well understood. The minor yearly shifts in the antigenic or immunogenic structure of the virus have been well described. That's what accounts for the promulgation of new flu epidemics each year. The susceptible pool hasn't encountered the newest variation in the virus. In addition, about every seven to ten years, there is a major shift in the influenza virus that is responsible for a larger number of cases - pandemic rather than epidemic cases of influenza. In fact in the last couple of years, we have had light flu seasons in this part of the world.

In the case of SARS virus I think it's too early to tell if there will be variations of this order. Certainly any viral agent, in order to survive, can effect small variations in its genetic makeup, so it's hard to predict what a virus is going to do specifically. But the typical mutations in the outer coats and surface proteins that are known in flu virus is not clearly known yet for this coronavirus.

Body1: Technology has helped develop proactive initiatives by public health officials and scientists. But will containment efforts catch up with SARS' rapid spread? Is a vaccine near?

Dr. Zinner: I think we have proof that containment works if it can be enforced and the procedures and regulations are followed. I know several colleagues in Canada who submitted to quarantine in order to help minimize the spread of the disease.

A vaccine, obviously, would be preferable. However, vaccine development is not simple work; it's a very tedious process. Fortunately, that process has been speeded up with tremendous advances in molecular biology and technology, so that it is possible to develop a candidate vaccine pretty rapidly. There are already several possibilities, as I understand - several candidates.

I think it's absolutely remarkable, almost miraculous, the way medical technology has sped discovery. So much is known about SARS virus, so much has been uncovered down to the molecular level in a span of only weeks, I'm hopeful that this will translate to an effective vaccine as rapidly as possible. Similarly, some fruitful treatment options could emerge. At the moment, as far as I know, there is no therapy that is proven effective. Several possibilities have been tried, but I am not confident whether they have really influenced the natural course of the disease yet.

The problem with getting a vaccine into the human population - and this is a good thing - is that we have safeguards in place to make sure that vaccines are appropriately and carefully tested. You would not want a vaccine to cause more problems than the disease! That testing by its very nature takes time. It is unlikely that we will have a vaccine on the market within less than two years, despite the rapid advances in science.

Body1: SARS in the New York Times and other journals has been viewed as another disease most likely caused by human-animal proximity, the way Lyme disease is animal-borne or the way AIDS probably originated among primates.

Dr. Zinner: Since this disease first was uncovered in a rural, agrarian society, the likelihood of something "jumping" from a common animal source to a human source is real. The fact that this virus or similar viruses have been found in some wild and domestic animals in China is not surprising. It makes the case for a possible spread of this agent from some animal source. It's a possible scenario, judging from news reports. It's impossible to prove in the short period.

There are many precedents for this, certainly. Animals, including birds, do spread viruses. One of the theories for the emergence of HIV (human immunodeficiency virus) postulates that it mutated from a monkey source to people in parts of the world where contact with monkeys or monkey blood is possible.

Body1: So the question is, what's next?

Dr. Zinner: Remember, 27 years ago Legionnaire's disease was new and unknown. Now we know what causes it and how to treat it. We didn't have Lyme disease, or at least had never recognized it, 28 years ago. Now we know how to diagnose and treat it.

This leads back to your first question. Infectious diseases are always going to be with us. I think the challenge for people in my field of public health and epidemiology is to have systems in place to recognize new problems, get them reported appropriately, and to develop mechanisms for diagnosis, control and treatment. I think that's just what's happening with SARS.

People should take some heart from this. We have not seen in the United States any spread of SARS outside of the expected risk groups, namely returning travelers who acquired their illness in one of the known areas associated with SARS. So it hasn't spread outside that group of patients and the health care workers and family members who take care of those patients. I am not trying to underestimate the import and impact of this very serious disease, but I think the risks so far have been extremely low.

Last updated: 23-Jul-03

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