medwireNews: A Swedish study of children admitted to hospital within the first year of life for lung infection has found that the increased risk this poses for later development of asthma is exacerbated by low gestational age.
Early respiratory infection and preterm birth are both known to be markers of increased subsequent asthma risk, but the relationship between these two factors has been unclear.
The researchers used national Swedish register data to identify the vast majority of respiratory infections in the first year after birth that resulted in hospital admission between 1981 and 1995.
Children who developed early severe lung infections (n=4233) were individually matched for gestational age, region of birth, and the month and year of birth with children who did not develop such infections (n=211,594). Each exposed child was matched with five unexposed children, or as many as were suitable.
Subsequent development of asthma was identified from registers of inpatient and outpatient diagnoses, and a register of prescriptions was used to identify pharmaceutical treatments for asthma in children and young adults. To avoid inflating the levels of asthma diagnoses , only children in which asthma was the sole diagnosis made after a hospital visit were included, explain lead author Scott Montgomery, from Örebro University Hospital, and colleagues.
The authors found that early respiratory infection was associated with asthma after age 5 years across all gestational ages, after adjustment for potential confounding factors such as maternal asthma and smoking (hazard ratio [HR)=1.51). However, the highest magnitude association was among the most preterm infants (gestational age less than 28 weeks; adjusted HR=2.22).
This association for the most premature held for asthma diagnoses both after age 10 years and age 16 years; however, the magnitude of the association was somewhat reduced after 16 years.
Writing in BMJ Open, Montgomery et al suggest that “the combination of early infection and prematurity may conspire to increase allergic as well as non-allergic risks for asthma, helping to explain the multiplicative effect of this combination of exposures for the risk of subsequent asthma.”
“The notably higher risk of asthma associated with this exposure combination continues throughout childhood, but appears to be less profound after age 16 years, possibly reflecting age-associated changes,” they conclude.
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