Public health in the twentieth century: advances and challenges.

Substantial advances in public health methods, practice, and the health of the public have occurred in the twentieth century. Some of the contributions most notable for their impact on mortality and longevity are vaccine development and widespread use, smallpox eradication, large reductions in communicable disease epidemics, and the rise and decline of several serious chronic diseases. Many methodological advances have facilitated better understanding of disease processes and opportunities for control. Epidemiological methods have advanced, but studies often ignore the determinants of health at the community level and above, leading to simplistic formulations of multiple risk factors contributing to chronic and other diseases and injuries. Occupational and environmental health developed as disciplines in this century, making significant contributions to current and future population health. The health care system became more organized, technologically sophisticated, and costly. New tools to assess health and the burden of ill health, to improve the effectiveness of interventions, and to measure economic effects of alternative investments promise greater efficiency and effectiveness for public health. An increasingly fragmented public health infrastructure must confront unprecedented challenges including dramatic global population growth, increased aging of the population associated with enhanced longevity, and possible irreversible changes in key environmental health determinants.