Public Health Efforts and the US Mortality Transition.

• Author: Anderson, D. Mark
• Position: Research Summaries

In the mid-1800s, mortality rates in US and Western European cities were much higher than those in rural areas. Since then, urban mortality rates have fallen dramatically. Driven by reductions in infectious diseases and diseases of infancy and childhood, this phenomenon is often referred to as the mortality transition and has been recognized as one of the most significant developments in the history of human welfare. (1) By the 1940s, the mortality "penalty" from living in a major urban center had all but disappeared in modern, developed countries. (2)

Economists originally attributed the mortality transition to increases in income, the onset of modern economic growth, and improved nutrition. (3) However, more recent analyses have stressed the importance of public health efforts, particularly efforts to supply clean water to the residents of major American cities. (4)

In a series of papers, we revisited the causes of the US urban mortality decline at the turn of the 20th century. We explored the role of clean water technologies and estimated the effectiveness of other public health efforts that were seen as vital to reducing food-related and waterborne diseases, including the building of sewage treatment plants; requirements that municipal milk supplies meet strict bacteriological standards; and requirements that milk come from tuberculin-tested cows. We also explored the determinants of the Black-White infant mortality gap in the first four decades of the 20th century and studied the extent to which public health efforts contributed to the narrowing of this gap. Finally, we estimated the effects of the US campaign against tuberculosis (TB) on pulmonary TB mortality during the early 1900s. The US anti-TB movement pioneered many of the strategies of modern public health campaigns, but its effectiveness had not been studied in a systematic fashion by previous researchers.

Public Health Efforts and the Decline in Urban Mortality

Previous research suggests that the US mortality transition was driven primarily by public health interventions aimed at reducing food-related and waterborne illnesses. (5) However, because the same city would often implement several interventions within a span of a few years, it has been difficult for researchers to isolate the effect of any single intervention, especially when taking a case-study approach.

Using data from the US Census Bureau's Mortality Statistics and Vital Statistics of the United States on 25 major American cities for the period 1900-1940, we conducted a statistical horse race to distinguish the effects of ambitious, often very expensive, public health interventions. (6) Figures 1 and 2 illustrate the rollout of the water-and milk-related interventions, respectively, for our sample of cities.

Consistent with the results of several previous studies, (7) we found that filtering the municipal water supply led to large reductions in typhoid mortality. Although we found no evidence that adding chlorine to drinking water, building sewage treatment plants, or testing dairy cows for TB were effective, filtering the water supply was also associated with an 11 to 12 percent decrease in infant mortality and a 14 percent reduction in diarrhea/enteritis mortality. While these estimates were measured with precision, they were not nearly large enough to explain the overall declines in infant and diarrheal mortality observed during the period 1900-1940. Our findings are inconsistent with David Cutler and Grant Miller's widely cited finding (8) that water filtration was a large contributor to the mortality decline. (9)

Water Purification Efforts and the Black-White Infant Mortality Gap

In another study, we explored the relationship between clean water technologies and the Black-White infant mortality gap during the period 1906-1938. (10)

Werner Troesken observed that urban Blacks and Whites lived in close proximity--"almost side by side"--at the turn of the 20th century. (11) He famously hypothesized that, because of this lack of residential segregation, it was costly to deny Blacks access to clean water, and that fear of...