Abstract
It remains uncertain why most infectious disease mortalities disappeared before modern medical interventions. Historical epidemiology using prospectively collected U.S. Army data from the Civil War (1860-1861), Spanish-American War (1898-1899), and First World War (1917-1918) suggests that epidemiological isolation was a major mortality risk factor for soldiers. Morbidity and mortality due to common infections decreased progressively from 1860 to 1918, except for influenza during the 1918 pandemic. Adult measles or mumps infections are indicative of isolated rural populations and correlated with disease mortality by U.S. state. Experiencing infections before adulthood may equip the immune system to better resist infections and decrease mortality rates.