RESUMEN
INTRODUCTION: The Swine Origin A H1N1 Influenza Virus (SOIV) pandemic emerged in April 2009 affecting people and health-care systems worldwide. This study examined the differences among the early clinical features presented in confirmed SOIV cases, those who tested negative for SOIV infection, fatalities, and hospitalized cases. METHODOLOGY: We reviewed 1,024 initial medical records of patients presenting with acute respiratory symptoms who attended the respiratory emergency room of a general hospital in Mexico and had a confirmatory test for influenza AH1N1 by RT-PCR from April to December 2009. RESULTS: Out of 1,024 cases, 457 (44%) were men with a mean age of 31±17 years; however, of these, SOIV confirmed cases were younger (26±8, p=0.000). SOIV infection was confirmed in 36% of the patients. Most (%?) cases presented mild infection, 20% of the patients required hospitalization, and 0.09% patients died. Asthma was more frequent in confirmed cases (p=0.028). Presence of COPD, systemic arterial hypertension, and diabetes mellitus was significant in confirmed hospitalized cases. Pulmonary rales, wheezing, and sudden symptom onset were more frequent and statistically significant in confirmed patients. Influenza-like illness was more frequent in confirmed cases (p=0.049). CONCLUSIONS: This study presents one of the largest series of the new SOIV infection confirmed by RT-PCR reported. This infection is frequently mild and affects mainly young adults. Sudden symptoms onset, pulmonary rales, and wheezing are early features of this infection. Asthma, COPD, systemic arterial hypertension, and diabetes mellitus should be identified to identify potentially severe and fatal cases. ILI helps distinguish SOIV infection.