Before revision: In the early 20th century it was a leading cause of death in children, but even before the Second World War and the introduction of antibiotics, its severity was already declining, perhaps due to better living conditions, the introduction of better control measures, or a decline in the virulence of the bacteria.
After revision: In the early 20th century it was a leading cause of death in children, but even before World War II, and the introduction of antibiotics, its severity was already declining, perhaps due to better living conditions, the introduction of better control measures, or a decline in the virulence of the bacteria.