Epidemiologic studies of Streptococcus pneumoniae in infants. The effects of season and age on pneumococcal acquisition and carriage in the first 24 months of life.

In a study of the natural history of pneumococcal carriage and infection in infants enrolled at birth in Birmingham, Alabama from November 1974 to December 1975, the authors observed patterns of acquisition and carriage that appeared to be influenced by age and the season of the year. To describe more precisely these effects, the original data were used to construct multiple regression models for acquisition, carriage rates, and duration of carriage of pneumococci during the first 24 months of life. The acquisition rate was strongly seasonal, with a marked winter peak and summer low. Seasonal rate increased with age, while the duration of carriage decreased; these combined effects were reflected in the carriage rate, which increased sharply up to the age of nine months, then leveled off. While age and season accounted for a relatively small part of the variation in acquisition and carriage rates, the models were found to fit the data very well. The authors were able to analyze the data in a precise fashion, confirm earlier observations, and relate them to the work of other investigators over the past 50 years.