Prospective cohort study of patient demographics, viral agents, seasonality, and outcomes of influenza-like illness in Mexico in the late H1N1-pandemic and post-pandemic years (2010-2014)

Influenza-like illness (ILI) caused by respiratory viruses results in various respiratory clinical manifestations. The ILI002 prospective observational cohort study aimed to describe viral agents, seasonality, and outcomes of ILI patients during four seasons in the influenza H1N1-pandemic and post-pandemic years (2010-2014). Patients from 6 Mexican Hospitals were enrolled from April 2010 to March 2014. Clinical data and nasopharyngeal swabs were obtained and tested for viral respiratory pathogens by real-time reverse-transcription polymerase chain reaction. Of 5662 enrolled subjects, 64.9% were adults and 35.1% children. Among 5629 participants with single pathogen detection, rhinovirus (20.2%), influenza (11.2%), respiratory syncytial virus (RSV) (7.2%), and coronavirus (6.8%) were most frequent. Co-infection occurred in 14.5% of cases. 49.3% required hospitalization, particularly in RSV cases (42.9% adults, 89.6% children). The mortality rate was 2.8% higher in elderly participants and those with comorbidities. Influenza H1N1 had the highest mortality rate, yet almost half of the deceased had no pathogen. Rhinovirus persisted year-round, while influenza, coronavirus, and RSV peaked during cooler months. Analyses showed that some viruses causing ILI may lead to severe disease and hospitalization irrespective of comorbidities. These findings may help the public health and policies on prevention measures, vaccination, treatment, and administration of healthcare.