Patients were characterized as confirmed, probable or possible cases of 2009 influenza A (H1N1) [20] according to the findings in the respiratory samples collected on admission. Some specimens, however, were not analyzed because laboratories soon became overloaded, especially at the beginning of the pandemic. As of 25 September 2009, the weekly update of the Ministry of Health reported that in patients ≥5 years with influenzalike illness, the 2009 influenza A (H1N1) virus had displaced other respiratory viruses in 93.4% of the samples processed [23, 24] . As a result of this, probable and suspected cases were considered as caused by the novel virus and were so included in the study.