Death rate for Tuberculosis, 1860-1960, United States, Source: US Bureau of the Census, Historical Statictics of the United States; Colonial Times to 1970 (Washington, D.C.:Government Printing Office, 1975), Part 1 pp58,63. Note: Data between 1860 and 1900 for Massachusetts only.

Ecological Determinants of Disease
The 19th century change in the pattern of disease was more than a direct cause-effect relationship of improved sanitation to reduced death rates from infections, aided by a change in values and behaviour. The respiratory diseases that caused many, often most of the deaths, were neither aggravated much by absence of sanitation nor alleviated by installing drains and piped water supplies. The death rate from tuberculosis began to fall in the early 19th century and continued to fall steadily long before the discovery of effective chemoprophylactic regimens virtually wiped out the disease in the rich nations in the 1950s. The same was true of other lethal respiratory diseases.

Interpretation of these observations has been much debated. Many other things were happening. Prosperity led to improved housing conditions and better nutrition. Literacy increased. It became less common for several children in the family to share the same bed. Being well-fed, better housed, well-informed, and separated from others by enough space to reduce the probability of person-to-person transmission of infection, all helped to reduce the burden of premature death. Perhaps there was also a rise in the natural (maternal to infant) level of immunity to some of the infections that had previously carried off huge numbers of infants and children, and a decline in the virulence of some of the most lethal pathogens. As McKeown has pointed out, improved health owes less to advances in medical science than to the operation of natural ecological laws[12].