In an observational study of 543 hospitalized patients with H1N1 influenza A infection in Spain, 43 % of the 243 patients in which chest radiographs were performed had pneumonia, 83 % of the 210 patients who had microbiologic confirmation had primary influenza pneumonia, and the remaining 17 % had concomitant secondary bacterial pneumonia. Bilateral pneumonia occurred in 48.3 % of patients; Streptococcus pneumoniae being the most frequent pathogen [14] . Several reports have identified methicillinresistant Staphylococcus aureus (MRSA) as the etiologic agent for severe community acquired pneumonia (CAP) in otherwise healthy young patients with influenza [15] [16] [17] . In another study that investigated the incidence of communityacquired MRSA pneumonia in H1N1 influenza patients, 50 patients of 4491 (1 %) laboratory-confirmed pandemic influenza A (H1N1) cases had a bacterial respiratory tract pathogen. The most commonly cultured organisms were S. pneumoniae (16 patients), S. aureus (13 patients) and Haemophilus influenzae (9 patients); MRSA was detected in only 2 patients [18] . In contrast, among 838 children and adolescents admitted to 35 intensive care units in the U.S. with confirmed or probable severe H1N1 influenza A infection, 48 % of the 71 patients with suspected diagnosis of early S. aureus coinfection had MRSA [19] .