Age Incidence of the Common Communicable Diseases of Children: A Study of Case Rates among All Children and among Children Not Previously Attacked and of Death Rates and the Estimated Case Fatality

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Abstract
Data from a number of sources on the percentage of children of specific ages who gave a history of a past attack of certain of the common communicable diseases of children were combined to secure an average percentage of those attacked. The diseases included were measles, whooping cough, mumps, chicken pox, scarlet fever and diphtheria. In spite of some errors in such observations, it appears that the data are a fairly accurate and complete record of the proportion of the population of specific ages that, on the average, has been attacked by these diseases. The data considered in this study are chiefly from urban communities of moderate size, but they include some distinctly rural areas. By the time adult ages have been reached, nearly 90% of persons have been attacked by measles, 75-80% by whooping cough, 70-75% by mumps, 50-60% by chicken pox and 10-15 % by scarlet fever. Ten to fifteen per cent have suffered clinical attacks of diphtheria, but as many as 60% give a negative Schick reaction, indicating an immunity to diphtheria. The percentage of persons of different ages who have been attacked may be considered as representing an accumulation of cases in a hypothetical population observed from birth to adult ages. By computing the difference between the percentage who had been attacked at successive ages there is secured an approximation of the incidence rates of these diseases at specific ages. The maximum incidence varies from about 3 yrs. for diphtheria to about 8 yrs. for mumps. After the maximum is reached, the rates in every case decline rapidly as age increases. By relating this total incidence rate for a specific age to the proportion of children who have not previously suffered an attack, there is approximated the incidence of the disease among the relatively susceptible group of children of a specific age who have not previously suffered an attack. The maximum incidence of measles, whooping cough, chicken pox and scarlet fever among children who have not previously been attacked and the maximum incidence of diphtheria among children with positive Schick test occurs at about 6 yrs. of age. It appears that, on the average, children who have not suffered attacks of these diseases prior to school entrance are more likely to be attacked during their 1st school yr. than at any other time. After the maximum, the incidence rates among children who have not previously been attacked decline considerably as age increases. Death rates were computed for children of specific ages in the registration area of the U. S. A. for the period, 1917-1923. With the exception of diphtheria the maximum death rate in every instance comes at an earlier age than the maximum case rate. By relating the death rates and the case rates an approximation of the case fatality of these diseases is secured. In every instance the maximum fatality occurs under 1 yr. of age. The fatality of measles, whooping cough and mumps declines to an almost negligible percentage by 5 yrs. of age, but the decline for scarlet fever and particularly diphtheria is by no means as great as in the other 3 diseases.

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