INTRODUCTION:

The objective of this study was to determine the risk factors associated to bronchiolitis in infants less than two years of age.

MATERIALS AND METHODS:

Prospective case-control study was performed in a hospital of second level of attention. The sample size was calculated for a level of confidence of 95, a power of 90, and a difference of exposure of 15 between cases and controls. For each case, there was one control matched for age and sex. The cases were obtained in the pediatric emergency room and the controls were healthy infants who came to the preventive medicine service of the same hospital. The diagnosis of bronchiolitis was established by direct observation in accordance to clinical criteria and chest X-ray. All the patients were weighed to the moment to be included in the study, and through structured interview the following variables were investigated: family history of bronchial asthma and atopy in immediate family members, prematurity, mechanical ventilation, bronchopulmonary dysplasia, present-day breast-feeding, length of time of breast feeding, early weaning, passive tobacco smoke exposure, maternal smoking, housing and living with domestic animals. The global significance of the study was probed by multiple logistic regression.

RESULTS:

Were studied 110 pairs with a range of age of 10 days to 23 months (average of 7.1 +/- 4.7 months), 49 pairs were female and 61 male (ratio 1:1.2) The variablÚs significantly associated (P < or = 0.05) to bronchiolitis were family history of bronchial asthma in immediate family members (OR: 2.9, IC 95 1.29-6.34) and prematurity (OR: 3.0, IC 95 1.04-8.87). The early weaning(OR: 0.44, IC 95 0.24-0.79) and present-day breast-feeding (OR: 0.53, IC 95 0.30-0.95) revealed a significant negative association. The other studied variables didn't show statistically significant association with bronchiolitis.

CONCLUSIONS:

Factors that increase the risk of bronchiolitis are a history of prematurity, and family history of bronchial asthma. Factors that have a protective effect are early weaning, and present-day breast-feeding.