Risk factors for invasive disease among children in Spain

To identify the risk factors related to invasive disease caused by Haemophilus influenzae type b (Hib), Neisseria meningitidis, and Streptococcus pneumoniae.

Case-control study. All hospitals of the region of Valencia in Spain (covering 95% of the population of Valencia). The patients are children aged less than 15 years in whom Hib, N. meningitidis or S. pneumoniae are isolated from normally sterile sites.

From 1995 to 1998, 275 cases of invasive disease were analysed, and 243 hospital controls were selected in the month after the onset of the case. The paediatrician completed a survey administered to the relatives at the time of admission. The risk factors related to invasive disease by Hib were exposure to tobacco smoke (number of smokers, adjusted OR (aOR) 1.74, 95% confidence interval (CI) 1.02-2.96) and living with more than four people (aOR 3.72, 95% CI 1.3-3.7). For N. meningitidis, there is a dose-response relationship; if more than 60 cigarettes are smoked daily at home, the aOR is 3.61 (95% CI 1.04-12.57). If there are more than four people living in the household, aOR 1.69 (95% CI 1.01-2.85). In children under two years of age, having siblings less than 15 years of age (OR 1.76, 95% CI 0.75-4.17) and attending a day nursery represents a risk for suffering invasive pneumococcal disease (aOR 4.21, 95% CI 1.28-13.83).

Among the variables tested, the modifiable risk factor is smoking; if smoking was reduced at home, the number of cases of invasive disease could be reduced in children, mainly in those under 5 years of age. Identification and vaccination of these risk groups would significantly reduce these diseases.