How deadly is seasonal influenza-associated pneumonia? The German Competence Network for Community-Acquired Pneumonia

The emergence of new influenza virus subtypes has rekindled the interest in the clinical course and outcome of patients with influenza-associated pneumonia. Based on prospective data from 5,032 patients with community-acquired pneumonia (CAP) included in the German Competence Network for Community-Acquired Pneumonia (CAPNETZ), we studied the incidence, clinical characteristics and outcome of patients with influenza-associated CAP and compared these findings with patients without influenza. Diagnosis relied on a positive PCR for influenza in throat washings. 160 patients with influenza-associated CAP were identified (3.2% of total population, 12% of those with defined aetiology). 34 (21%) patients with seasonal influenza had a concomitant pathogen (mostly Streptococcus pneumoniae). Patients with influenza-associated CAP were significantly older, had been vaccinated less often and had preceding antibacterial treatment less often. 30-day mortality was low (4.4%) and not different to that of patients with pneumonia caused by bacterial (6.2%) or viral (other than influenza) pathogens (4%). Patients with influenza plus a bacterial pathogen (mixed influenza-associated pneumonia) had a higher mortality than those with pure influenza-associated pneumonia (9% versus 3.2%). Mortality was higher in patients with mixed compared with pure influenza-associated pneumonia. However, we could not observe any excess mortality in patients with influenza-associated pneumonia.