Interactive effect of family history and environmental factors on respiratory tract–related morbidity in infancy

Background

Family and environmental factors affect the development of respiratory morbidity. How these factors interact is unclear.

Objective

We sought to clarify the interactive effect of family history of asthma and environmental factors on the occurrence of respiratory morbidity.

Methods

Two hundred twenty-one infants with a positive family history of asthma (PFH) and 308 with a negative family history of asthma (NFH) were prenatally selected and followed until the age of 2 years. Exposure to environmental factors and the occurrence of respiratory morbidity were recorded. By using multiple logistic regression analysis, increased risk was expressed in odds ratios (ORs) adjusted for relevant covariables.

Results

Infants with a PFH had more respiratory morbidity than infants with an NFH. Adjusted ORs ranged from 1.7 (95% CI, 1.0-2.8) for expiratory wheezing to 4.9 (95% CI, 1.7-13.6) for croup. Parental smoking increased the OR of a PFH for wheezing ever (OR, 5.8 [95% CI, 2.5-13.8]) and attacks of wheezing (OR, 6.8 [95% CI, 2.7-16.9]), as did Der p 1 (OR, 10.2 [95% CI, 2.8-36.3] and OR, 7.1 [95% CI, 7.1-21.0], respectively). Exposure to both parental smoking and Der p 1 further increased this OR (OR, 30.8 [95%, CI, 6.9-137.2] and OR, 26.2 [95% CI, 5.9-115.6], respectively). Breast-feeding decreased the ORs of PFH for tonsillitis and acute otitis media: the increased ORs for these diagnoses in formula-fed infants with PFHs versus those with NFHs (OR, 9.2 [95% CI, 2.1-39.7] and OR, 2.9 [95% CI, 1.1-7.2], respectively) was attenuated in breast-fed infants (OR, 1.8 [95% CI, 0.8-3.8] and OR, 0.7 [95% CI, 0.4-1.3]).

Conclusion

Parental smoking and Der p 1 increase the effect of a PFH on respiratory morbidity. Breast-feeding reduces this effect.

Clinical implications

Extra attention should be given to stimulate mothers to breast-feed their children in case they cannot stop smoking or taking sanitation measures.

Key words: Genetic predisposition to asthma, risk factors, respiratory signs and symptoms, infants, parental smoking, house dust mite, breast-feeding

Abbreviations used: GP, General practitioner, NFH, Negative family history of asthma, OR, Odds ratio, PFH, Positive family history of asthma, PPS, Postnatal parental smoking