As the COVID-19 pandemic ravages communities worldwide, evening news reports are filled with maps, each with different symbols and bright colors, showing statistics ranging from numbers infected to deaths in an area. Maps are now a key part of our toolkit for pinpointing, quantifying, and tracking the spread of disease over time. But this systematic approach to epidemiology—the study of disease spread and control—was largely nonexistent for most of history.
Epidemiology as a discipline rose to prominence during the time of cholera. The cholera pandemic of 19th century England—spanning over three decades and killing over 38 million—bears many similarities to today’s COVID-19 pandemic, which has already taken the lives of over three-hundred thousand individuals throughout the world. Originating in India, an English colonial possession, cholera was brought over to England through travelers who moved between the two regions, ultimately resulting in four major outbreaks in the British Isles that claimed tens of thousands of lives.
In October 1831, the first known case of a cholera patient—William Sproat—was detected in Sunderland, a city in northern England. He died within three days after contracting the disease.
When cholera reached London a year later, the disease spread quickly and easily. The underdeveloped infrastructure of the city, coupled with overcrowding, created the conditions for this disease to thrive, especially in the under-resourced communities called the “slums.”
Prominent doctors and researchers at the time were quick to label the disease as airborne, transmitted from decaying organic matter called “miasma.” Moreover, most of the elite saw cholera as a scourge of the poor, as demonstrated in a Board of Health report that blamed the spread of the disease on “the poor, ill-fed, and unhealthy part of the population, and especially those who have been addicted to the drinking of spirituous liquors, and indulgence in irregular habits.”
Efforts to improve the city’s sanitation system only compounded existing socioeconomic rifts. Plans involved dumping the raw sewage of the city into the river Thames, which served as the main source of the city’s water. Since most public figures at the time believed this illness was airborne, they believed that they had found an effective solution to the problem. However, this plan disproportionately affected the poor, many of whom lived by the Thames. Consequently, the number of cases continued to rise, spreading into the wealthier districts of London and resulting in another outbreak that claimed the lives of over 14,000 individuals.
Learning from the pattern of the outbreaks, physician John Snow spurned the prevailing misperceptions regarding the disease’s mode of transmission and began to create a rational method for determining the root cause of the pandemic. Finally, in 1854, Snow demonstrated—through extensive testing and data collection—the connection between water contamination and cholera in his home district of Soho, an area particularly impacted by the disease.
Interviewing his neighbors and others in his community, Snow developed a map, annotating it with bars proportional to the number of infected individuals per household on each street. Snow’s maps were remarkably accurate cartographically, even marking details such as alleyways and street corners. Although methods for annotating maps with technical information such as topography were part of the mapmaker’s toolkit before Snow’s time, his application was especially unique, using the maps to visually illustrate and analyze a medical phenomenon.
After employing dots to show varying concentrations of cholera cases in different parts of the city, he noticed clusters around particular areas and discovered the disease’s source: a hand pump on Broad (now Broadwick) Street.
Snow’s work was one of the first public health studies ever conducted. At first, however, his findings were not widely accepted by his peers. Many in the medical establishment saw this new method of science as foreign and unfounded, yet were forced to reconsider.
Today, Snow is acknowledged as the founder of epidemiology and advanced data science. Bringing together his humanitarian concerns, his passion for science, and his creative use of mapmaking, Snow showed how the sciences and humanities, when used in concert, can provide breakthrough solutions for the pressing problems we face as a society.
As we confront a global health challenge of historic proportions, Snow’s pioneering work has become especially relevant, inspiring geospatial models that enable scientists, policy-makers, activists, and historians to come together to establish potential solutions for COVID-19 with a proper understanding of the scale and scope of the virus.
