Parental smoking
This is the first study to show that severity in SAB infants is associated with the fact that their parents smoked. The differences found in the rate of IMV and PBI between these 2 groups were clinically relevant. Infants with SAB whose parents smoked needed to be intubated in 27 additional cases per 100 patients compared with those whose parents did not smoke. This result means that 58% of the intubations in the group of infants whose parents smoked were due solely to the fact that their parents smoked.
In addition, IMV duration and PICU length of stay were also significantly higher in smoke-exposed patients.
The higher risk for ETI and need for IMV can be most likely explained by the fact that patients exposed to tobacco smoke have a higher bacterial superinfection rate, as we can see in ETA cultures of intubated patients (71% positive if parents smoked vs. 21% positive if the parents did not smoke).
Both groups have similar characteristics. The only significant difference between these two groups was gestational age. Although there were slight differences in gestational age, the median of both groups corresponded to term infants.
Cigarette smoking has been shown to be a substantial risk factor for important bacterial and viral airway infections. The mechanisms by which smoking increases the risk of infections include structural changes in the respiratory tract and a reduction in the immune response18.
ETS exposure is known to be an important risk factor for childhood lower respiratory tract infections19. Passive ETS exposure has been associated with lower oxygen saturation and higher clinical severity scores20, and it significantly increases the risk of hospitalization for bronchiolitis in the first year of life21. Furthermore, maternal cigarette smoking during pregnancy puts children hospitalized with bronchiolitis at significantly higher risk of intensive care use, and postnatal ETS might exacerbate this risk22.
The findings in our study imply that in infants with SAB, the risk of a severe event, such as intubation, is increased by ETS exposure. All these infants survived because they received appropriate treatment in a PICU. Bronchiolitis is a significant cause of respiratory disease worldwide, and appropriate access to a PICU is not guaranteed for all infants.
This study has some limitations. The sample we analyzed consisted of only 102 patients. However, it represents the complex PICU population with SAB, a situation that physicians face on a daily basis, and this sample has similar characteristics to others reported23,24.
Memory-based parental reports of short-term ETS exposure can play an important role in quantifying ETS exposure in infants and children25. The degree of exposure to tobacco smoke is not known, nor is the duration of time the patients were exposed. Further studies are needed to measure the ETS exposure of the children who have AB, and to know if this risk factor could be removed, consequently reducing the severity of bronchiolitis in these patients, and the number of patients requiring IMV or PICU stay.