Infectious disease mortality in the United States decreased markedly during most of the 20th century. The sharp increase in 1918 and 1919 was caused by the influenza pandemic, which killed more than 20 million people world wide, including over 500,000 people in the US. Following World War II, it was widely believed that humans were winning the war against infectious microbes. Life threatening diseases such as tuberculosis and typhoid fever could be treated with antibiotics, and dreaded childhood diseases (polio, whooping cough, diptheria) could be conquered with vaccination. Coupled with improvements in urban sanitation and water quality, vaccines and antibiotics dramatically reduced the incidence of infectious diseases.

But, in 1950, penicillin began to lose its power to cure infections caused by Staphylococcus aureus. In 1957 and 1958, new strains of influenza emerged in China and spread around the world. In the 1970’s, there was a resurgence of sexually transmitted diseases and new diseases identified in the US and elsewhere (Legionnaire’s Disease, toxic shock syndrome, Lyme’s disease). During the 1980’s, HIV emerged as a new infection and tuberculosis re-emerged in an antibiotic resistant form. Between 1980 and 1992, the death rate from infectious diseases increased 58%. The increase in drug resistance in strains of bacteria forced the US to return to the pre-antibiotic era in the battle against many common organisms, at the same time that new bacterial and viral pathogens were appearing.