because most deaths from pertussis occur in the young , death rates were determined for consecutive five-year periods from 1900 through 1974 among children younger than one year of age ( infants ) and among those from one to four years of age . there was an accelerated decline in mortality beginning in 1940 , especially among infants ( p < 0.01 vs. mortality in 1930-1939 ) .
C0008059
children
C0021270
infants