Metaphor is useful. When Malcolm Gladwell wrote about an epidemic of Hush Puppies, no one thought that Hush Puppies were transmissible in anything more than the metaphorical sense. But as doctors we need to be more careful before we muddy the meanings of our technical words. An epidemic is a widespread occurrence of an infectious disease in a community at a particular time. Yes, its second dictionary meaning is a sudden, widespread occurrence of an undesirable phenomenon (perhaps Malcolm Gladwell disliked Hush Puppies), but we are doctors. Transmissible diseases demand aspects of prevention and treatment and population response not relevant when considering diseases that are not transmissible. That is one reason for guarding its meaning, but the other is the last phrase of the definition: at a particular time. The world has recently seen a perfect and unpleasant example: the epidemic of Ebola in West Africa. As I write, the number of new cases is falling: it was a widespread occurrence of an infectious disease, and it occurred at a particular time. We are lucky that it did not become pandemic: prevalent over a whole country or large part of the world; or endemic: regularly found in a particular people or in a certain area. These words need to be protected because they have particular meanings that are important to communicate.
It is not possible to be sure when epidemic was first applied to a non-communicable disease, but searching PubMed for the ill-conceived phrase epidemic proportions gives clues. It first appeared in 1922, in a report of mouse typhoid. The infecting Bacillus species were described as causing “self-limited outbreaks of disease reaching at times epidemic proportions.” But the “proportions” are what make an outbreak of disease an epidemic. Weather forecasters are criticized for saying “blizzard conditions,” when it is the conditions – wind, snow, poor visibility, drifting – that make it a blizzard. Thus, Bacillus species caused “self-limiting epidemics;” the other words are superfluous. At least typhoid is an epidemic disease, unlike the other medical maladies that surface during a search for epidemic proportions. In order of their first appearance, they include injuries and deaths from road traffic accidents (1964), drug use by the young (1969), cancer (1971), obesity (1977), osteoporosis (1993), chronic pain (1994), atrial fibrillation (2002), and Alzheimer’s disease (2003).
It does not take much insight to realise that most of these maladies are largely the result of there being no real epidemics to carry people off, and that the upsurge of epidemics is simply a reflection of increased longevity and a perceived need for a disease to be pushed into the limelight. Diabetes and obesity are the maladies most commonly attached to epidemic, often in the same article. They are also most commonly of epidemic proportions, with cardiovascular disease a distant third. It may be even worse than that, for the spectre of pandemic proportions surfaced in 2000, though there is lack of consensus on whether obesity “has reached,” “is reaching,” or is as yet only “an escalating threat” of pandemic proportions.
People are born, grow up, get ill, and die. It is not sensible to describe the diseases that are inevitably going to be become more common as epidemics. Although not spotted in my searching on epidemic proportions, searching specifically for macular degeneration, hip fractures, chronic obstructive pulmonary disease, and allergy revealed that they, too, are epidemics. Not only is cancer as a whole an epidemic but, individually, lung cancer, mesothelioma, skin cancer (melanoma and squamous cell cancers separately), colorectal cancer, breast cancer and thyroid cancers are also epidemics.
It may not be sexy, but “increasing prevalence” is the correct description for what is happening to obesity, Alzheimer’s disease and cancer. The tabloids won’t relinquish epidemics of diabetes and pandemics of heart failure, but the journals should. It is common rhetoric, when writing of epidemics, to invoke tides: “the rising tide of diabetes,” “turning the tide of obesity.” I should like to stem the tide of epidemic proportions, fearful of the metaphor overload if “the world is heading for a vascular tsunami of pandemic proportions.”
Competing interests: None declared
Neville Goodman is a writer and retired consultant anaesthetist, Bristol UK.