Dulling Occam’s Razor: The Challenge of Emerging Infectious Diseases When Applying the Single Explanation Principle in Public Health Policy
In February 2003 dozens of people began to suffer from high
fevers accompanied by mild respiratory symptoms in several locations in
“All things being equal, the simplest explanation is the best one,” according to a principle attributed to the thirteenth-century philosopher William of Ockham. Following this logic, the anticipated pandemic was almost certainly in progress in 2003—a single viral strain was the simplest explanation for the similar symptoms. But scientists and policymakers employing Occam’s Razor, so often reliable, would have slipped badly in this case. What was actually occurring was a coincidence of three viral outbreaks: the primary emergence of what came to be called Severe Acute Respiratory Syndrome (SARS), which did eventually spread to multiple countries on several continents, an episode of H5N1 avian influenza, and another episode of H7N7 avian influenza.
These three diseases striking in the winter of 2003, observed in the context of the recent reappearance of the H5N1 strain, also show that Occam’s Razor still cuts too sharply when it comes to presumptively advocating a single contagion-control method to stem potential pandemic threats. In 2003, the two avian strains had a direct connection to animals (zoonosis)—being spread to humans by their direct association with avian species, but not observed spreading readily from human to human—whereas SARS was found to be readily contagious over short distances between people (little was observed about its ability to spread to or through animal populations). Since then, SARS has not reappeared, but the H5N1 flu has, and scientists are carefully monitoring for a mutation which would make interhuman contagion possible. Such mutations, often beyond the awareness of the public, mean that even if only one viral agent is evident, it is possible that it may be transmitted through multiple pathways: by droplets, through the air (aerosol), by interchange of bodily fluids, or through contamination of environmental surfaces (“fomites”).
The underlying complexity of the viral illnesses observed in February 2003 has lessons for those combating natural outbreaks of diseases in the future and for those anticipating intentionally-generated bioevents (infectious biological agents used as terrorist devices); it highlights the potential disconnect between the tendency common among scientists and politicians to look for a single workable philosophical solution and the fact that there can be more than one explanation for a given set of symptoms, and thus there might be more than one response to them.
In order to work effectively against the threat to public health from emerging infectious diseases, scientists and policymakers should be aware of the general inclination to try to find a single (causal) explanation for similar illnesses that are temporally related, but that eventually may turn out to be caused by more than one emerging infectious disease.
Master of Science course in “Emerging Diseases: Past as Prologue”.
Daniel R. Lucey, MD, MPH
Director, Center for Biologic Counterterrorism and Emerging Diseases
ER One Institutes,
Georgetown University Department of Microbiology and Immunology