Shift in the age-distribution of meningococcal disease as predictor of an epidemic?

Demographic data for several years before, during, and after an epidemic of meningococcal meningitis show that the age-distribution of the disease shifts considerably during an epidemic--although the highest incidence of meningococcal infections was still that among children under 5 years old, the proportion of patients aged greater than 4 years increased significantly. The ratio of the number of cases aged over 4 years to that aged up to 4 years was 0.833 and 0.775 in two non-epidemic periods, but 2.95 and 2.29 in two epidemic years. Careful demographic surveillance may reveal the approach of a meningococcal epidemic sooner than do the present surveillance methods.