Microbiology, 2021

16.2 • Tracking Infectious Diseases 657
Incidence of Four Notifiable Diseases in the United States, Week Ending January 2, 2016
Disease
Current Week
(Jan 2, 2016)
Median of Previous
52 Weeks
Maximum of
Previous 52 Weeks
Cumulative
Cases 2015
Chlamydia
trachomatis infection
11,024 28,562 31,089 1,425,303
Giardiasis 115 230 335 11,870
Gonorrhea 3,207 7,155 8,283 369,926
Table 16.1
LINK TO LEARNING
The current Morbidity and Mortality Weekly Report (https://openstax.org/l/22mortweekrep) is available online.
CHECK YOUR UNDERSTANDING
• Describe how health agencies obtain data about the incidence of diseases of public health importance.
16.2 Tracking Infectious Diseases
Learning Objectives
By the end of this section, you will be able to:
• Explain the research approaches used by the pioneers of epidemiology
• Explain how descriptive, analytical, and experimental epidemiological studies go about determining the
cause of morbidity and mortality
Epidemiology has its roots in the work of physicians who looked for patterns in disease occurrence as a way to
understand how to prevent it. The idea that disease could be transmitted was an important precursor to
making sense of some of the patterns. In 1546, Girolamo Fracastoro first proposed the germ theory of disease
in his essay De Contagione et Contagiosis Morbis, but this theory remained in competition with other theories,
such as the miasma hypothesis, for many years (see What Our Ancestors Knew). Uncertainty about the cause of
disease was not an absolute barrier to obtaining useful knowledge from patterns of disease. Some important
researchers, such as Florence Nightingale, subscribed to the miasma hypothesis. The transition to acceptance
of the germ theory during the 19th century provided a solid mechanistic grounding to the study of disease
patterns. The studies of 19th century physicians and researchers such as John Snow, Florence Nightingale,
Ignaz Semmelweis, Joseph Lister, Robert Koch, Louis Pasteur, and others sowed the seeds of modern
epidemiology.