Asthma and severity of 2009 novel H1N1 influenza: a population-based case–control study

Abstract

Background Asthma has been shown to be associated with an increased risk of the 2009 novel H1N1 influenza (H1N1) infection among children. However, little is known about the role of asthma in severity of H1N1 infection. Objective To determine the association between asthma and other atopic conditions and severity of H1N1 infection. Patients and Methods We conducted a population-based case-control study. Cases were all Olmsted County, MN residents admitted to the hospital within a week of a positive test for H1N1. Controls who had a positive H1N1 but were not admitted to hospital were individually matched to cases with regard to birthday, gender, clinic registration date, diagnostic method, and calendar month of influenza testing. Asthma was ascertained using predetermined criteria. Data were fit to conditional logistic regression models. Results There were 46 eligible individuals admitted to hospitals with H1N1 infection during the study period. Ninety-seven controls were individually matched to their corresponding cases. Among cases, 23 (50%) were male and 29 (63.0%) were Caucasians. The median age at hospitalization was 20.7 years. Twenty-five (54.4%) cases had asthma before the date of hospitalization, compared to 33 (34.0%) controls (matched OR: 2.31; 95% CI, 1.13–4.73; p=0.02). This association approached statistical significance after adjusting for all pertinent covariates (adjusted matched OR: 2.55; 95% CI, 0.98–6.64; p=0.055). Conclusion Asthma may be associated with severe H1N1 infection. In addition to timely influenza vaccination for asthmatics, consideration for prophylactic treatment for unimmunized asthmatics with significant exposure to influenza and immunized asthmatics with early flu-like symptoms should be given.

Risk factors for serious outcomes associated with influenza illness in high‐ versus low‐ and middle‐income countries: Systematic literature review and meta‐analysis

“…In the review of studies that provided estimates adjusted for the presence of other factors known to impact the risk of hospital admission for people ill with influenza, we found similarly heterogeneous estimates. There were no adjusted estimates that were significantly and consistently (across studies) outside the confidence bounds of the estimated pRR from this meta‐analysis …”

Influenza in Asthmatics: For Better or for Worse?

“…The increase in hospitalization among asthmatics may be attributed to a variety of factors including altered health seeking behavior (and in parents of asthmatics), heightened awareness due to media coverage, accelerated triage, and elevated physician precautions. Comparative analyses between seasonal and pandemic influenza concluded that the frequency of hospitalization and death as well as the profile of common underlying diseases, including asthma, were actually similar ( 116 – 119 ) although pH1N1 infections induced more severe disease in older age groups ( 120 ) and those with poorly controlled asthma ( 121 ) compared to seasonal strains. Therefore, greater attention to underlying diseases as risk factors during Swine Flu may have been due to the fact that pH1N1 induced more morbidity and mortality compared to the seasonal influenza virus strains that preceded it.…”

“…The age of onset and endotype often determines the chronicity of asthma and maintenance medication use. Patients that were not on long-term therapeutics to control asthma symptoms had a higher incidence of pH1N1 infection ( 120 , 121 , 134 , 135 ). While the pH1N1 virus did increase the number of asthma exacerbations compared to seasonal strains ( 126 ), virus infection did not correlate to the severity of asthma symptoms ( 126 ).…”

Risks for infection in patients with asthma (or other atopic conditions): Is asthma more than a chronic airway disease?

“…55 Other studies reported both an increased risk of H1N1 infection among children with other atopic conditions (adjusted OR, 1.89; 95% CI, 1.15-3.12) 56 and more severe H1N1 infection (risk of hospitalization) among those with than without asthma (matched OR, 2.31; 95% CI, 1.13-4.73). 57 Two independent studies identified asthma as the single most common comorbid condition among patients with severe H1N1 infection (hospitalization or death), with rates of asthma ranging from 10% to 32%. 58-61 …”