The Age Incidence of Poliomyelitis in Connecticut 1921-1947 *

In reviewing this subject briefly, one finds that at the turn of the century, "infantile paralysis," as it was then called, was considered to be "rather rare after the age of six."' Indeed more than 50 per cent of the cases were under two years of age. In one of the earliest epidemics in the United States, occurring in Vermont in 1894, 90 out of the 120 cases whose ages were given were under the age of six.3 Today, however, in Scandinavia1'8 as well as in northern United States,7 poliomyelitis is seemingly no longer a disease of infants; perhaps 70 to 80 per cent of the total cases occur in people over the age of five, and as high as 25 per cent in people over the age of 15 years. This gradual shift in the age of the patients has apparently not taken place in some parts of the world, but in others it has progressed at varying rates during the past thirty years or so. The State of Massachusetts furnishes data in this regard, as originally exemplified by the studies of Forsbeck and Luther,6 who observed no apparent change in age distribution of cases until 1918, twenty-five years after the initial epidemic in that state. After this time there occurred a marked decrease in the relative number of cases in the age group under five years, with a "compensatory" increase in the relative number of cases in the 5-14 age group. The percentage of cases in the older age groups was found to remain more or less constant. Subsequently, in Connecticut, Knowlton'1 reported an increased percentage of cases over five years of age occurring in the 1931 series of cases as compared with the percentage distribution of cases in this age group for earlier years. And Wenner,2' in a study of poliomyelitis in the city of New Haven and adjacent areas, found that about 25 per cent fewer children under five years were reported to have had the disease in 1943 as compared with 1916. A reciprocal increase was seen in the 5-9 and 10-15 age groups. But it is not enough to indicate that the percentage of cases of poliomyelitis in the different age groups has shifted over the years-because, unless their shift is analyzed on the basis of age-specific rates, it may be found to be more apparent than real. In