Protective effect of breastfeeding:: an ecologic study of Haemophilus influenzae meningitis and breastfeeding in a Swedish population

In Orebro County, Sweden, a 2.5-fold increase in the incidence of Haemophilus influenzae (HI) meningitis was found between 1970 and 1980. In a case-control study of possible risk factors for invasive RI infection conducted in the same area, 1987-1992, breastfeeding was found to be a strong protective factor. Material and methods In order to study the relation between incidence rates of HI meningitis between 1956-1992 and breastfeeding rates in the population an ecologic study was performed. Results A strong (negative) correlation between breastfeeding and incidence of KI infection 5 to 10 years later (rho(xy) (s) approximate to -0.6) was seen, whereas no relation seems to exist for the lime lag 15 years and beyond. The correlation for contemporary data was intermediate. There were similar results for the breastfeeding proportions at 2, 4 as well as 6 months of age. Discussion Our ecologic data are consistent with results from our case-control study. The time-lag for the delayed effect on the population level could be estimated although sparse data make the estimates vulnerable to sampling fluctuations. Limitations with ecologic studies are discussed. Conclusions There seems to be an association between high breastfeeding rate in the population and a reduced incidence of I-II meningitis 5 to 10 years later. These results do have implications on strategies for breastfeeding promotion, especially in countries where Rib vaccination is too costly and nor yet implemented.