Incidence of Infectious Disease in the First Three Years of Life, Related to Social Circumstances

The association between the incidence ofmorbidity in the first 2 years of life and social class (defined according to the occupation of the father) has been examined in two recent communications. Using data for Luton, Grundy (1949) reported no association between "social class" and morbidity; using data from a National sample, Douglas (1951) noted a consistent social gradient in the incidence of disease. The results of these inquiries have evoked some discussion of differences, which are not in fact very great. Douglas's generalization about a social gradient in morbidity rested mainly on an association in the first 2 years of life between the incidence of lower respiratory infection and occupation of father. The Luton investigation has since been extended to cover the first 5 years (Dykes, Grundy, and LewisFaning, 1953), and it has beenconcluded that although there was no consistent association between "social class" and the incidence of illness, "the respiratory infections show an upward gradient for the first year of life". Data presented by these authors in their Tables indicate that a similar gradient existed for the first 2 years combined. What seems clear is that, in some parts of Great Britain at least, the relationship of "social class" with morbidity in infancy is not very striking, and the much sharper association with mortality must be attributed largely to differences in case-mortality. But it by no means follows from this that the incidence of morbidity in infancy is no longer much affected by the environment. There are reasons for doubting whether in this context the occupation of the father provides a sufficiently sensitive index of social circumstances (much less of environment in general); the most important reason is perhaps that it takes no account of family size. Gibson and McKeown (1952) showed that infant mortality in Birmingham in 1947 was more sharply related to maternal age and birth rank than to the standard of housing in the wards in which infants were domiciled. These differences were almost wholly attributable to deaths from infectious disease; for example, among children of mothers aged less than 25 years, the incidence of death from infection between the second and twelfth months was under twenty (per 1,000 children alive at 1 month) in the first born, and over eighty in the fourth and later born. The magnitude of the differences in mortality made it seem worth exploring the association between morbidity and maternal age and birth rank. Data for this purpose were obtained shortly before or after the third birthday from mothers of certain children born in Birmingham during 1947 (the selection of this sample has been described by Lowe and Gibson, 1953). Each mother was asked to provide details of her child's illnesses during the first 3 years of life, but attention is here restricted to specific infections of childhood, including pneumonia, diarrhoea and vomiting, and otitis media. Diarrhoea and vomiting are included only if a medical practitioner was consulted. Bronchitis and coryza are excluded. Histories were recorded in respect of 1,782 children (77 per cent. of the original sample). In 39 cases data were incomplete, and the examination of morbidity which follows is based on 1,743 children.