PROTECTIVE EFFECT OF BREAST-FEEDING ON INVASIVE HAEMOPHILUS-INFLUENZAE INFECTION - A CASE-CONTROL STUDY IN SWEDISH PRESCHOOL-CHILDREN

Background. In Orebro County a 2.5-fold increase in the incidence of H aemophilus influenzae (HI) meningitis was found between 1970 and 1980, an observation that initiated the present study. Materials and method s. In order to search for associations between morbidity in invasive H I infection and possible risk factors, a case-control study was conduc ted over a B-year period from 1987 to 1992, before general Hib vaccina tion was introduced in Sweden. Fifty-four cases with invasive Hi infec tion and 139 matched controls were studied for possible risk factors s uch as day-care outside the home, short duration of breastfeeding, pas sive smoking, low socioeconomic level of the household, many siblings in the family, allergy, frequent infections, repeated antibiotic treat ments and immunoglobulin deficiency. Results. Multivariate analysis sh owed a significant association between invasive HI infection and two i ndependent factors, i.e. short duration (<13 weeks) of exclusive breas tfeeding, odds ratio (OR) 3.79 (95% confidence interval [CI] 1.6-8.8) and history of frequent infections, OR 4.49 (95% CI : 1.0-21.0), For t he age at onset 12 months or older, the associations were stronger, OR 7.79 (95% CI : 2.4-26.6) and 5.86 (95% CI : 1.1-30.6), respectively. When breastfeeding duration in weeks was analysed as a continuous vari able the OR was 0.95 (95% CI : 0.92-0.99), indicating a decreased risk with each additional week, Increased OR were observed for other risk factors as well but not of the magnitude found for short duration of b reastfeeding. Discussion. The association of decreased risk for invasi ve HI infection and long duration of breastfeeding was persisting beyo nd the period of breastfeeding itself. This finding supports the hypot hesis of a long-lasting protective effect of breastfeeding on the risk for invasive HI infection. Conclusion. A decreased risk for invasive HI infection with long duration of breastfeeding was found, Our result s do have implications for strategies in breastfeeding promotion, espe cially in countries where Hib vaccination is too costly and not yet im plemented.