For most of urban history, infectious disease was the primary cause of death in cities. Crowded housing, contaminated water, and poor sanitation created ideal conditions for epidemics that killed city residents at rates far exceeding those in the countryside. That pattern held for centuries, only shifting in the late 1800s and early 1900s as clean water, sewage systems, and public health measures brought infectious diseases under control. Today, heart disease and cancer have taken their place as the leading killers in cities around the world.
Why Cities Were So Deadly
The core problem was density. High population density favored the transmission of infectious diseases, while trade and migration constantly imported new pathogens. In cities like Philadelphia, New York, Baltimore, and Boston, tenement housing, severe overcrowding, and poor sanitation served as breeding grounds for illnesses like tuberculosis, cholera, and typhoid. Newcomers arriving in cities often lacked acquired immunity, and poverty made them even more vulnerable.
Before modern infrastructure, city water supplies were routinely contaminated with human waste. This made waterborne diseases like cholera and typhoid fever persistent killers. Cholera struck British cities in devastating waves in 1831, 1848, 1854, and 1866. In the United States, typhoid alone killed an estimated 35,000 people in 1900. By comparison, from 1999 to 2006, just three people in the U.S. died of typhoid, despite a population more than four times larger.
The Diseases That Killed the Most People
Tuberculosis was one of the most relentless killers in dense urban environments. It thrived in poorly ventilated, overcrowded housing and disproportionately struck the poor. In Philadelphia in the late 1800s and early 1900s, tuberculosis rates were elevated across the entire population, though Black residents were hit especially hard due to compounding factors of poverty, worse housing conditions, and lack of access to care.
Scarlet fever, now easily treatable, was one of the most feared childhood diseases of the 19th century. It was the leading cause of death among children aged one to nine in England during the 1850s and 1860s. Epidemics erupted suddenly in cities across Britain, Scandinavia, and the United States in the 1830s, and these outbreaks explain much of the sharp rise in childhood mortality during that period. Between roughly 1830 and 1870, cities experienced heightened mortality driven largely by scarlet fever and sanitation-related infections, particularly among children between 3 and 24 months old.
Cholera, typhoid, dysentery, and other diarrheal diseases rounded out the list. These waterborne illnesses cycled through cities in waves, sometimes killing thousands in a matter of weeks.
How Clean Water Changed Everything
The turning point came with investments in water filtration and sewage systems. These infrastructure changes, rather than medical breakthroughs, drove the initial decline in urban death rates. In lower-income countries where water disinfection programs have been studied more recently, childhood diarrheal disease mortality dropped by 45 to 67 percent following the introduction of treated water, though aging pipes and inadequate sanitation infrastructure sometimes weakened those gains.
This shift is part of what public health researchers call the epidemiological transition: a long-term change in which infectious disease pandemics are gradually replaced by chronic and degenerative diseases as the primary causes of death. In developed countries, this transition unfolded over the late 19th and 20th centuries. As fewer people died young from infections, more lived long enough to develop heart disease, cancer, and diabetes. At the same time, industrial development and urban living introduced new environmental hazards that contributed to these chronic conditions.
What Kills City Residents Today
In the modern United States, the leading causes of death are heart disease (roughly 681,000 deaths per year), cancer (about 613,000), and accidents (around 223,000). These numbers reflect the entire population, but the pattern holds in urban areas specifically.
What’s striking is that cities are now actually safer in terms of overall mortality than rural areas. In 1999, age-adjusted death rates in rural areas were 7 percent higher than in urban areas. By 2019, that gap had widened to 20 percent. Urban death rates fell from 865 per 100,000 to 693 per 100,000 over that period, while rural rates declined more slowly and then plateaued. In 2019, rural areas had higher death rates for all ten leading causes of death, with the biggest gaps in heart disease, cancer, and chronic lower respiratory disease.
Heart disease mortality specifically has fallen faster in cities than in rural areas. From 1999 to 2009, coronary heart disease mortality dropped 42 percent in large metropolitan areas but only 35 percent in rural areas. By 2007, rural heart disease death rates actually surpassed urban ones for the first time. Rural residents now tend to have higher rates of obesity and physical inactivity, fewer options for healthy food, and less access to affordable healthcare.
Air Pollution as an Ongoing Urban Threat
While infectious disease no longer dominates urban mortality, air pollution remains a significant city-specific risk. Fine particulate matter, along with pollutants like nitrogen dioxide, ozone, and sulfur dioxide, contributes to strokes, heart disease, lung cancer, and respiratory illness. The World Health Organization estimates that the combined effects of outdoor and household air pollution are associated with 7 million premature deaths globally each year. Cities concentrate both the sources of pollution and the people exposed to it, making air quality one of the most important ongoing public health challenges in urban areas.
Cities During COVID-19
The early months of the COVID-19 pandemic briefly revived the old pattern, with dense cities like New York experiencing explosive outbreaks. But as the pandemic progressed, the relationship flipped. Rural areas experienced higher rates of COVID-19 mortality during the Delta and Omicron waves, driven by limited access to healthcare, higher rates of underlying health conditions, and fewer critical care resources. Among over 3 million people infected with SARS-CoV-2, rural residents had a 19 to 26 percent higher risk of dying within two years of infection compared to urban residents, even after adjusting for background risk factors. The pandemic ultimately deepened the existing rural mortality disadvantage rather than restoring the historical urban one.