Nearly two centuries separate the two epidemics—one began four years ago this month and the other in the summer of 1832—but they are otherwise strikingly similar, and the parallels offer some lessons for public health officials today. A novel infectious agent, cholera, is introduced into an island population living in crowded and unsanitary conditions, killing thousands. The recent epidemic, of course, occurred on the impoverished island nation of Haiti. The earlier one unfolded 2,400 kilometers north, on the island of Manhattan. With narrative, interactive maps, “Mapping Cholera: A Tale of Two Cities,” provides a look at the searing pathways of two outbreaks.

The waterborne bacterial pathogen that causes cholera, Vibrio cholerae, most likely arrived in Haiti with United Nations peacekeepers from Nepal, whose camp discharged sewage into a stream that fed into the nation’s largest river, the Artibonite.1 The bacteria spread south to the capital city of Port-au-Prince, where dense urban crowds lacking reliable access to clean drinking water and sanitary systems were already reeling from a magnitude 7.0 earthquake that had hit in January 2010. Haiti had not been exposed to cholera for over a century—so the population had not acquired even limited immunity to infection. Within nine months, Haiti had more cholera victims than the rest of the world combined.2

View the full screen interactive. Interactive by Dan McCarey.

The international humanitarian nongovernmental organization Doctors Without Borders (MSF) spearheaded the international response to the epidemic in Haiti, treating more than half the reported cases. “Mapping Cholera” uses the GPS data collected by MSF on thousands of cases, along with several years’ of reporting that I have conducted to document the Haitian epidemic from 2010 to 2014. During that time period, more than 700,000 Haitians fell ill and more than 8,000 died.3

In 1832 cholera arrived in Manhattan via the Hudson River and the newly opened Erie Canal. In the slums at the epicenter of the outbreak population density was nearly six times greater than it is today. The disease sickened 5,800 New Yorkers—more than 2 percent of the city’s population—and killed nearly 3,000.4

Frustrated by public health authorities’ failure to notify city residents about the spread of the disease, a group of private physicians banded together to issue daily bulletins on the scourge’s progress. “Mapping Cholera” combines the historical addresses of the cases the doctors collected with 19th-century maps recently geocoded by the New York Public Library. The map of this epidemic, which has never been plotted before, predates by over two decades the anesthetist John Snow’s famous 1854 map of a cholera outbreak in London, which proved that cholera spreads in contaminated water and helped launch the field of epidemiology.

Ending cholera in New York City took decades. The disease continued to plague Manhattan and the rest of the U.S. until the widespread adoption of public drinking water and sewer systems at the turn of the 20th century. Haiti has yet to enjoy the benefits of such infrastructure. Although the U.N. in 2012 launched a 10-year plan to provide clean water and sanitation on the island of Hispaniola, which Haiti shares with the Dominican Republic, only a fraction of the $2.2 billion required has been raised.