In which century were communicable diseases the leading cause of death?

• A. 18th
• B. 19th
• C. 20th
• D. 21st

Answer: (C)

Mortality from infectious diseases has varied as societies improve living conditions, vaccines, and treatments—the epidemiologic transition. In the 20th century, public health advances such as cleaner water and sanitation, widespread vaccination programs, and the advent of antibiotics dramatically reduced deaths from communicable diseases, and these infections remained the dominant killers for much of the century in many populations. This era sets up a broad pattern where infectious diseases were the leading cause of death before the late 20th century shift toward chronic, non-communicable diseases. That’s why the 20th century is the best choice among the options.