Clinical Characteristics and Mortality of Influenza A H1N1 and Influenza-Like Illness in Mexico City in the 2013-2014 Winter Season.

BACKGROUND: The 2013-2014 influenza season in Mexico City was severe and mainly due to influenza A H1N1, as was the 2009 pandemic. OBJECTIVE: To describe features of the outbreak and to compare the characteristics of patients with and without viral identification. METHODS: We reviewed the medical charts of all individuals with influenza or influenza-like illness admitted to a referral hospital for respiratory diseases in Mexico City from January 2013 to March 2014, whether influenza virus was identified or not. RESULTS: We included 233 patients with influenza-like illness, 99 of whom had laboratory confirmed influenza; one-half of all patients required mechanical ventilation and 25% were admitted to the intensive care unit. Patients with confirmed influenza had a more severe disease than those without confirmation. A total of 52 (22.3%) patients died in hospital; survival was greater among patients hospitalized in the intensive care unit compared with those who remained in regular wards. CONCLUSIONS: Influenza A H1N1 continues to cause significant outbreaks in Mexico City. Patients with influenza-like illness had a similar clinical course regardless of laboratory confirmation of influenza, suggesting that their illness likely belonged to the same outbreak. Mechanical ventilation in regular hospital wards may be lifesaving, although the outcome is worse than at an intensive care unit.