While a number of advances have been made in our understanding of the epidemiology of acute respiratory infections in the past two decades, a number of serious questions still require urgent answers. The associations of factors such as chronic disease in adults, direct smoking, passive smoking, crowding, and breast feeding to acute respiratory infections are now well documented. Appropriate changes in public health policy need not be predicated on results from still further studies. However, in virtually all of the other areas cited in this review, further data are required. In developing countries, studies being currently conducted on vitamin A supplementation, malnutrition, and indoor air pollution will help address the most pressing issues. More studies are also needed on the relations between HIV infection and acute respiratory infections, as well as low birth weight and respiratory infection. The National Research Council studies have provided important additional data on etiologic agents in children in developing countries, but data on adult pneumonia remain sparse. In developed countries the issues that may be of greatest interest are the relation between maternal antibody levels and passive immunity in infants, the reasons for the increase in pneumonia mortality in older age groups, and the relation between air pollution and acute respiratory infections (as opposed to morbidity from bronchial reactivity). From a methodological viewpoint, the relation between previous respiratory infection (particularly in the first year of life) and subsequent acute respiratory infection morbidity has been inadequately explored. Adjustment for autocorrelation in multivariate models may be necessary if this relation is strong. Greater standardization of data collection methods in developed and developing countries also needs to be more seriously addressed. Given that some advances have been made in this area, the time may be right for development of acute symptom questionnaires, akin to the American Thoracic Society chronic respiratory questionnaire, for use in both developed and developing countries. Standardization of diaries, although somewhat more difficult, would also be extremely useful in many instances.
PIP: Virtually only researchers from developed countries have done studies of risk factors for acute respiratory infections (ARIs) since these countries have an infrastructure that can support large multidimensional epidemiologic studies while developing countries do not. Yet results from these countries studies are not always relevant to developing countries since risk factor exposures in developing countries. For example, the predominant problem in developing countries is that ARIs in children is that ARIs in children 5 years old often result in death whereas in developed countries morbidity predominates. Based on studies in developed countries, there is plenty of evidence that strong associations exist between ARIs and chronic disease in adults, direct and passive smoking, and breast feeding. Thus policy need not request additional studies to base proper changes in public health policy. Yet researchers do need to collect more data on the associations between ARIs and HIV infections, low birth weight, and other possible risk factors. In fact, some are now examining relationships between ARIs and malnutrition, vitamin A supplementation, and indoor air pollution in developing countries. Some of the more important issues in developed countries are the links between maternal antibody levels and passive immunity in infants, the links between air pollution and ARIs, and the reasons for a rise in pneumonia in the aged. Another area that scientists need to explore is the association between respiratory infection (especially between 1-12 months old) and subsequent ARI. Further epidemiologists should standard data collection methods in both developed and developing countries. For example, the chronic respiratory questionnaire of the American Thoracic Society can serve as a model for acute symptom questionnaires.