COVID-19 ONE MORE MYSTERY FOR EPIDEMIOLOGISTS
Hand washing’s benefits and cholera-water link are among their many discoveries
Trying to solve the mystery of a disease involves asking basic questions about who is affected, when they are affected, how they are affected and by what they may be affected. The task of finding appropriate answers is in the domain of epidemiologists — scientists who study the incidence, distribution, causes and control of diseases.
The ancient Greek physician Hippocrates may well be regarded as the founder of this discipline, based on his attempts to describe illnesses from a rational perspective, rather than ascribing causes to supernatural effects. Human ailments were not the result of vengeful gods, he maintained, and causes and treatments were best identified through careful, systematic observation. Life-threatening fevers were more likely to afflict people who lived in swampy areas, Hippocrates observed, although he failed to make the connection to mosquitoes. That link was finally made by American physician Walter Reed, but not until two millennia had passed.
The famous military hospital in Washington D.C., where for many years presidents were usually treated, was named after Reed. (It closed its doors a few years ago and now Reed’s name graces the U.S. national military medical centre in Bethesda, Md.)
Physicians should observe people’s behaviour, especially their dining and drinking habits, Hippocrates advised, and is therefore often credited with introducing the idea that diet can be both the cause and cure of disease.
The changing seasons, winds and vapours play a role in the spread of disease, he noted, and also suggested that sources of water should be considered when looking at disease patterns. He was correct, but water would not be identified as a conveyor of disease until the 19th century.
Essentially then, Hippocrates introduced the basic concept of epidemiology, namely that the key to elucidating the nature of a disease lies in the observation of all possible contributing factors.
Strangely enough, nobody donned Hippocrates’s mantle until the 17th century when Thomas Sydenham, eventually dubbed the “English Hippocrates,” published Observationes Medicae, in which he emphasized the importance of making observations rather than relying on ancient authorities. Curiously, one of those ancient authorities was Hippocrates, who had recommended that fevers be treated with heat, a therapy that according to Sydenham’s observations did not work.
The English doctor noted that the rich seemed to have a higher mortality rate from smallpox than the poor and concluded that bloodletting and the various toxic potions that were the treatments for smallpox at the time, and which were not accessible to the poor, were more dangerous than helpful. He also recognized the therapeutic value of humour, writing “the arrival of a good clown exercises a more beneficial influence upon the health of a town than of 20 asses laden with drugs.”
Sydenham was the first to use iron to treat iron-deficiency anemia, popularized the use of quinine to treat malaria, and promoted fresh air, exercise and a healthy diet. For pain, his solution was opium. After carefully observing its effects on his patients he concluded that “of all the remedies it has pleased almighty God to give man to relieve his suffering, none is so universal and so efficacious as opium.”
Curiously, although Sydenham promoted careful observation, he was not in favour of studying disease by means of autopsies, or even through the use of the recently introduced microscope. He was deeply religious and argued that God only gave man the ability to perceive the outer nature of things with his senses.
Epidemiology took on a decidedly scientific approach in the 18th century with Scottish naval surgeon James Lind tracing epidemics of scurvy among sailors to deficiencies in the diet, and famously recommending the inclusion of citrus fruits as a preventative.
Then in 1798, Edward Jenner made his classic observation that milkmaids previously afflicted with cowpox did not contract smallpox. This prompted him to try to protect people from smallpox by inoculating them with pus taken from cowpox pustules, marking the beginning of vaccination.
In the 19th century, epidemiology took two large leaps. Ignaz Semmelweis observed that women were more likely to die from childbed fever if, during birth, they had been assisted by a doctor rather than a midwife.
After studying many cases, he noted that the increased risk was likely from doctors unwittingly passing on some disease-causing substance picked up in the autopsy room. The solution? Hand washing!
John Snow, a contemporary of Semmelweis, investigated an outbreak of cholera in London and plotted on a map the houses where the afflicted lived. He found a cluster of the disease in and around Broad Street and traced the problem to a public water pump from which people drew water. He concluded — correctly — that cholera was somehow borne by the water and suggested that the handle of the pump be removed to stop the spread of the disease.
This insight is widely regarded as a pivotal point in epidemiology and is celebrated every year in London with the John Snow Society’s Pumphandle Lecture, traditionally accompanied by the ceremony of removing and then replacing the pump handle as a reminder of the continuing challenges to public health.
Hopefully, one day there will be a lecture on how the challenge of COVID -19 has been met.