Article abstract The clinical presentation of the novel swine-origin influenza virus (S-OIV) A (H1N1) appears to resemble that of seasonal influenza, and the majority of patients infected with the pandemic virus experience mild symptoms and recover fully within a week, even without medical treatment.The disease demonstrates a wide spectrum of clinical presentation, including asymptomatic infection or mild illness with a rapid recovery time without complications. The typical symptoms of 2009 H1N1 influenza virus may include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, fatigue, nausea, diarrhea, and vomiting. Depending on the case series, the proportion of persons with laboratory-confirmed 2009 H1N1 infection that is febrile ranges from ~10% to 50%. A minority of the cases present severe pneumonia, acute respiratory distress syndrome (ARDS) and multiorgan dysfunction syndrome that may progress to death. Mexico was one of the countries in which the illness produced high morbidity and mortality.