Asthma infection risk ‘goes beyond the airways’

Researchers from the USA have found that asthma may be associated with an increased risk for infections outside of the respiratory tract.

Multiple previous studies have shown that patients with asthma are more likely to experience bacterial infections of the airways, but Young Juhn (Mayo Clinic, Rochester, Minnesota) and team found that they also have a higher burden of community-acquired Escherichia coli bloodstream infection (BSI) than people without asthma.

The team studied data on 259 children and adults who had community-acquired E. coli BSI between 1998 and 2007 and an equal number of age- and gender-matched controls.

Compared with a rate of 6% in controls, 14% of patients with E. coli BSI had a history of asthma before the study. After adjusting for confounding factors, this equated to an independent 2.74-fold increased odds for E. coli BSI among patients with an asthma history. In patients with active asthma (ie, symptoms, treatment, or hospital visit/admission within the previous year), the risk was even greater at a 3.89-fold increased odds.

Overall, the population attributable risk percentage indicated that around 9% of all cases of E. coli BSI were due to the presence of asthma.

Other factors independently associated with E. coli BSI included non-Caucasian ethnicity, alcohol addiction, chronic renal insufficiency, immobility, being in receipt of immunosuppressive therapy, recurrent urinary tract infections, and urinary incontinence. However, neither atopic dermatitis nor allergic rhinitis were associated with the infection, which the authors say may be due to misclassification bias of these conditions.

Writing in BMJ Open, Juhn et al say that the reasons behind the association between asthma and E. coli BSI are unknown but they could relate to impairment of innate immunity induced by allergic sensitization. Additionally, patients with asthma may have an altered response to Gram-negative bacteria.

While there was a higher prevalence of E. coli BSI among asthma patients taking inhaled corticosteroids than in those who were not, this did not remain significant after adjustment. Furthermore, only two asthma patients were receiving systemic steroids at the time of BSI, indicating that steroid use was not a primary underlying factor in the relationship between asthma and infections.

The authors say that further studies will be needed to replicate their findings and explore the underlying mechanism.

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