What do we fear?

Sarah Borwein

As this Year of the Rooster draws to a close, it is both ironic and fitting that we are obsessed with thoughts of birds and bird viruses. One needs only open a newspaper or turn on a television to be bombarded with information about the looming pandemic of avian influenza. Much of the information provided is conflicting and confusing, adding to the rising anxiety levels in the community. As primary care physicians, patients often turn to us for accurate and balanced information. How can we help them to separate fact from fiction?

Perhaps the two most important things we can do are to know the facts ourselves, and to understand how our patients assess risk.

Highly pathogenic avian influenza (H5N1) first made the leap from birds to humans in 1997, when 18 people were infected in Hong Kong and 6 died. Molecular studies at that time showed that viruses from humans and poultry were virtually identical, indicating that the virus had jumped directly from birds to humans. Most human cases could be traced to direct contact with poultry. The outbreak ended after all of Hong Kong's 1.5 million poultry were slaughtered within three days. That rapid and decisive action is credited by many public health authorities with averting a pandemic of H5N1 influenza. Or perhaps it merely delayed it.

The crucial mistake made in the management of the Hong Kong outbreak was failing to trace the virus back to its origins. Had that been done, perhaps we would have been able to stamp out H5N1 among poultry before the disease had spread throughout the region. But that was before SARS and the brutal lessons learned about living in a highly interconnected world, the importance of transparency and the political will needed to prevent and contain epidemics. At the time, countries tended not to look beyond their own borders when dealing with outbreak control. And so now we find ourselves with an entrenched and probably unstoppable outbreak of avian influenza in poultry in Asia and elsewhere, and growing concern that a pandemic of human influenza is inevitable.

The Hong Kong experience in 1997 clearly demonstrated that H5N1 has pandemic potential. It also demonstrated for the first time that humans could be directly infected with a purely avian influenza virus, and thus also serve as a mixing vessel for the exchange of virus genes. Prior to 1997, it was believed that pigs were the obligatory hosts for reassortment of influenza virus genes. The recent resurrection of the 1918 "Spanish Flu" virus demonstrated that it was an avian virus that had adapted for human-to-human transmission. That finding clarified that there are two routes by which a pandemic virus might arise from an avian virus: it might swap genes with a human flu virus as happened in the milder pandemics of 1957 and 1968, or it might simply slowly adapt to humans as the 1918 virus did.²

It is all too easy to get the impression that a pandemic is about to erupt within weeks if not days. In fact, given the capricious and labile behaviour of influenza viruses, one cannot even be certain that H5N1 will be the cause of the next pandemic, let alone what the illness would look like or when it might happen. Reassortment events are unpredictable by nature, but there is some question as to why it has not already happened given that there has been ample opportunity over the past two years. If adaptive mutation is to be the route by which a pandemic strain emerges, it is likely that we would see gradually increasing clusters of limited human-to-human transmission and would thus have some time to take defensive action.¹

Apocalyptic predictions about a replay of the 1918 pandemic paint a picture of the virus becoming human-to-human transmissible while maintaining its current virulence. At the time of writing this editorial, the virus is known to have infected 130 humans of whom 67 have died, leading to the oft-quoted 50% mortality figure.⁴ This would indeed be a nightmare scenario, but it is unlikely to come to pass. The virulence of influenza viruses is usually down-regulated when they become more contagious¹. The current numbers are both too small to extrapolate and likely overestimates, as it is simply unknown how many mildly ill or asymptomatic cases there have been. It is worth remembering that even the devastating Spanish Flu epidemic of 1918-19 had a mortality rate of approximately 2.5%.⁵ It did share one worrisome epidemiologic feature with the documented human cases of avian influenza: the propensity to be most lethal in young, otherwise healthy adults.

While it is true that effective disaster planning requires envisaging the worst case scenario, individuals do not need to assume that they personally face high personal risk. In a pandemic with a 2.5% mortality rate in which 30% of the population is affected (this is close to a worst-case scenario), the average person would have less than a 1% risk of dying. There are parallels in the airline industry. Aviation safety professionals must consider every disaster that might occur in order to plan how to prevent them or at least mitigate their effects. But when passengers obsess about worst-case scenarios we call it catastrophizing and treat it as an anxiety disorder.

In medicine, we are often ruling out the most serious disorders even though we know that they are unlikely. The same approach applies to disaster planning: we hope for the best but prepare for the worst. In the wake of Hurricane Katrina - a catastrophe in which public health officials appeared to have hoped for the best and prepared for the best - publicity about pandemic planning has taken on new urgency. Unfortunately, that appears to be feeding a rising public hysteria.

Media scare stories create a wide spectrum of response in different individuals, ranging from complete nonchalance to full-blown panic. Most people are poor at assessing risks. Smokers (whose habit will kill 50% of them prematurely), may fret about air pollution, an insignificant risk in comparison to their habit. We incorrectly fear violence more than clogged arteries, homicide more than diabetes, pesticides more than skiing, and terrorism more than accidents. Some parents even have great difficulty accepting the minute risks of childhood vaccines despite overwhelming evidence in their favour. We live in a "culture of fear" but so often fear the wrong things.⁶

Why are our fears so often out-of-sync with reality? Psychologists have identified several influences on our intuitions about risk.⁷ First, we fear what we cannot control. Because we feel in control when driving and out of control when flying, fear of flying is much more common than fear of driving. We also fear what's immediate; hence is difficult to persuade a teenager of the risks of smoking when the danger appears to be far in the future. In addition, we fear the things that form vivid and indelible memories: images of a plane hitting the World Trade Centre, or a shark attacking a swimmer remain readily available in memory where they can provoke great anxiety despite the rarity of such events. We also fear the unexpected. Eight hundred SARS deaths terrify us much more than the 3000 daily toll of malaria, or the million annual deaths from the regular flu, statistics which are so familiar that they have come to seem banal.

Finally, we are genetically primed to fear the things our ancestry has prepared us to fear. Stone Age man was at risk from snakes, lizards and spiders; hence modern man still fears them. Fear of contagion and infection is one of our most deep-seated fears. During the SARS epidemic, we saw clearly that fear of contagion was in many ways more damaging than the disease itself.

The result of all these influences is the tendency to gauge risks and benefits very poorly: we overestimate our chances of winning the lottery, or of dying in a fiery plane crash or from avian influenza, and we underestimate our chances of having a stroke or a car accident. In that context, it is easy to see how the current publicity around avian influenza creates undue alarm. All of the factors are there: lack of control, unfamiliarity, a sense that it is imminent, vivid newspaper and TV images, and the appeal to one of our most primal fears.

As physicians, our challenge is to help our patients put the risks in perspective. Yes, a bird flu pandemic may happen, but there is no particular evidence that it is imminent. We do not know how severe the pandemic might be and there is no reason to assume the worst, except for purposes of pandemic planning. Simple measures such as hand-washing and social distancing will reduce individual risks during an outbreak, but in any case, in most scenarios the average person is likely to suffer a nasty flu from which they will recover. Helping patients to understand the difference between preparing for the worst on a societal level and catastrophizing on a personal level may be one of our most important jobs. In the end, it may not be the virulence of the emergent virus that determines the outcome of an influenza pandemic, but the way in which we manage panic.

For the first time in history, we have the advantage of advance warning of a pandemic. Instead of succumbing to anticipatory hysteria, we should seize this unprecedented opportunity to reduce its effects. Preparedness should lead to reassurance. We all need to take to heart the mantra "Prepare for the worst, but hope for the best".