Why Did Diseases Decline?

The 19th-century population shift from country to city that accompanied industrialization and immigration led to overcrowding in newly populated cities that lacked proper sanitation or clean water systems. These conditions resulted in repeated outbreaks of cholera, dysentery, TB, typhoid fever, influenza, yellow fever, and malaria.

By 1900, however, the incidence of many of these diseases had begun to decline because of public health improvements, implementation of which continued into the 20th century.

Sanitation & Hygiene

Local, state, and federal efforts to improve sanitation and hygiene reinforced the concept of collective “public health” action (e.g. to prevent infection by providing clean drinking water). By 1900, 40 of the 45 states had established health departments. The first county health departments were established in 1908 (6).

From the 1930s through the 1950s, state and local health departments made substantial progress in disease prevention activities, including sewage disposal, water treatment, food safety, organized solid waste disposal, and public education about hygienic practices (e.g. food handling and handwashing). Chlorination and other treatments of drinking water began in the early 1900s and became widespread public health practices, further decreasing the incidence of waterborne diseases.

Tuberculosis declines WITHOUT a vaccine

The incidence of Tuberculosis (TB) also declined as improvements in housing reduced crowding and TB-control programs were initiated. In 1900, 194 of every 100,000 U.S. residents died from TB — the second leading cause of death — and most were residents of urban areas.

In 1940 (before the introduction of antibiotic therapy), TB remained a leading cause of death, but the crude death rate had decreased to 46 per 100,000 persons. There was never a vaccine for Tuberculosis in the United States. Yet other countries TB rates also decreased before the TB vaccine was introduced.