Risk of Haemophilus influenzae type b meningitis in Polish children varies directly with number of siblings: possible implications for vaccination strategies.

Background: In the absence of an effective vaccine, Haemophilus influenzae type b (Hib) meningitis has frequently been found to be the most common bacterial meningitis among children less than or equal to 5 years of age. This study was conducted prior to the introduction of Hib vaccine in Poland, and is the first case-control study of Hib meningitis in this country.

Methods: A 1:3 matched case-control study was nested within a population-based surveillance study of Hib meningitis in children less than or equal to 5 years old in Poland. Controls were matched on the case's age at onset of disease and immunization center.

Results: Having one or more siblings is a highly significant risk factor for Hib meningitis and, under the rare disease assumption, risk increases linearly with the increase in the number of siblings. The size of the living area of the home was not itself a significant risk factor for disease. Breast-feeding was not protective in contrast to previous studies. Childcare outside of the home was a significant risk factor for Hib meningitis especially among children greater than 16 months of age, whereas the effect of sibling number on Hib meningitis was much greater among the younger children.

Conclusion: Risk of Hib meningitis approximately doubles for every unit increase in the number of siblings. Routine vaccination of Polish infants who have two or more siblings could potentially prevent half of the Hib meningitis cases.