Asthma in older people hospitalized with influenza in Spain: A case-control study.

BACKGROUND: Influenza infection is an exacerbating factor for asthma, and its prevention is critical in older patients with asthma.

OBJECTIVE: This study investigated the association between asthma and influenza-related hospitalization, in Spain, of patients ages ≥ 65 years and their clinical evolution.

METHODS: A multicenter case-control study was carried out in 20 Spanish hospitals during the 2013-2014 and 2014-2015 influenza seasons. Patients ages ≥ 65 years hospitalized with laboratory-confirmed influenza with and without asthma were matched with controls according to the presence of asthma, sex, age, hospital, and date of hospitalization.

RESULTS: A total of 561 patients with influenza (15.9% with asthma) and 1258 patients without influenza (8.0% with asthma) were included as cases and controls, respectively. The adjusted risk of influenza for patients with asthma was calculated by multivariate conditional logistic regression. The adjustment variables were the following: smoker/nonsmoker, pneumonia in the 2 years before hospital admission, previous oral treatment with corticosteroids, influenza vaccination during the seasonal campaign, Barthel index (ordinal scale used to measure performance in activities of daily living), level of education, obesity, and the presence of other comorbidities. Patients with asthma presented a great risk of influenza (adjusted odds ratio 2.64 [95% confidence interval, 1.77-3.94]). Compared with patients without asthma, patients with asthma had more symptoms, and these had been present for longer before admission but presented a lower hospital or postdischarge mortality.

CONCLUSION: This study indicated that asthma was associated with hospitalization from influenza A infection. Although patients with asthma and with influenza had more symptoms, hospital or postdischarge mortality was lower, probably due to a better response to medical treatment.