The dreaded mad cow disease has finally arrived. How worried should we be? Should you avoid the range cattle you come across on hikes in Montana or skip that steak when you visit Bozeman?
This issue is complicated by scientific complexity and strong emotions ingredients for error. Given their limited resources, how can policymakers most effectively protect public and environmental health?
The situation invites "risk analysis." This process comprehensively and quantitatively considers the nature of the hazard, exposure, severity (death or something less from that exposure), epidemiology, and toxicology.
The U.S. Department of Agriculture asked our Center in 1998 to analyze the risk of mad cow disease in the U.S. For three years we studied everything from the natural history of this strange disease to on-the-farm practices to slaughtering and rendering. This work enabled us to construct a computer model simulating the introduction of mad cow disease to American cattle.
The good news from the simulation in terms of health risk to other animals and humans is simple little happens. Our analysis found that even if compliance is imperfect, government's ban on feeding cattle protein back to healthy cows chokes off the disease. Additional measures, which the USDA implemented after a mad cow was discovered in Washington, reduce the low risk even further.
Risk analysis also often weighs the benefits and costs of various risk-reduction/health-improving strategies. For each, we consider the number of lives saved, diseases prevented, quality of life protected and the cost of each strategy. The goal is to identify how our society's limited resources can do the most good.
Some object to such antiseptic analysis. They find placing a dollar value on human risk morally unacceptable. Explicitly quantifying risks to life and assigning dollar values may seem harsh. However, we commonly allocate funds for our own health and safety. Consider smoke detectors and new tires, expensive health insurance or whole-body MRI exams. If we can't have it all, we intuitively balance the benefits and costs of alternatives. For policymakers, risk analysis makes such decision-making more honest and explicit.
Debates about risk issues are often emotionally heated and charged with competing values. Risk analysis applies a cooler, science-based perspective. The resultant insights favor no ideology, no political or corporate agenda. It's entirely reasonable to use the neutral tools of decision science and risk analysis to sort among various health threats. The goal is to identify choices that will benefit the most people at the least cost.
However, as psychologist Paul Slovic and others have found, personal perception of risk is an emotional, intuitive, instinctive process. We fear risks that kill us in dreadful ways shark attacks for example more than deaths that seem relatively benign, like heart attacks. Fears about risks to kids (abductions), risks that are new (SARS), risks that are fraught with uncertainty (the Washington, DC sniper), risks over which we have no control (flying), all demonstrate that the emotional aspects of a risk matter as much as the odds.
Certainly policy makers in a democracy must consider these emotions. The USDA has done just that with mad cow disease, recalling meat that is not considered a risk and imposing a series of increased controls. This will further reduce an already small risk and help reduce fear.
But money, time, and attention applied to "panic button" risks divert resources from greater risks. As a result, some exposed to greater risks will get sick or die. Mad cow disease displaced flu from front pages. Yet flu will cause 20,000 to 30,000 or more deaths in the U.S. this year. To promote public health, policymakers must identify these larger risks and cost-effective responses. Risk analysis fosters clarity when we're considering such problems.
Our ancestors lived in a world where many (perhaps most) threats were obvious. But we lack the luxury of that simplicity. Our modern world, with all its benefits, comes with a bewildering web of potential threats. Our instinctive responses are often wrong. Thinking logically about our perils, and carefully analyzing our choices for dealing with them, is an important way to identify the preferable solutions. Risk analysis helps us maximize public and environmental health and safety.
FREE board member George Gray is Executive Director of the Harvard Center for Risk Analysis at the Harvard School of Public Health. David Ropeik is HCRA's Director of Risk Communications.
February 5, 2004
My family and I lived in the United Kingdom from August 1993 to June 1994. As a result of our having spent more than six months in the UK during this period, we cannot donate blood in the United States. Both my daughter and I had been regular blood donators, but the Red Cross and other blood banks no longer permit us to donate.
Every time I see a plea for blood donations, I wonder about the basis of this prohibition. I have not heard of anyone contracting the human variant of mad cow disease through a blood transfusion. I wonder what is being done about blood donations and transfusions in the UK. I haven't heard of any contamination there either.
From 1997 to 2000 my daughter was in school in Montana and tried to give blood. She was told that she couldn't. She was also told that the state was suffering from a severe shortage of blood since a major source of blood donations came from a nearby Air Force Base. Unfortunately, most of the members serving there had been posted previously to Great Britain and could no longer donate.
Has there been any evidence of Creutzfeld-Jacob disease originating from a blood transfusion? Will there be a change in the rules regarding who can donate blood in the U.S.? How long does this prohibition go on before it becomes apparent that a potential blood donator is "not contagious"?
To date, as far as we know, there has not been any case of vCJD (variant Creutzfeld-Jacob disease) that has been definitively ascribed to blood transfusion. However, there has been one suspicious case in Britain of a person who developed vCJD symptoms after receiving blood from a donor who also had symptoms. Thus it may be the case that it is transmissible through blood transfusions.
It is not clear how long the prohibition will continue. You might contact the American Red Cross or the FDA for futher information.
Ruth Kava, Ph.D., R.D.