Incidence of Typhoid Fever, 1920-1960.  With the implementation of disinfection methods of drinking water, there has been a drastic decline in cases of typhoid fever in the United States. In 1920, the incidence of typhoid fever in the U.S. was 33.8 per 100,000 population, which was a decrease from approximately 100 per 100,000 population in 1900. In 1930, the incidence was less than 20 per 100,000 population; in 1940, it was less than 8 per 100,000; and by 1960 the incidence of typhoid fever in the U.S. was less than 1 per 100,000.