This study evaluated subjects without Influenza Like Illness (ILI) symptoms for the presence of respiratory viruses and allowed comparison to the ILI 002 study population over a period of 28 days. This observational substudy started on November 2013 and was completed on May 2014 with an enrollment of 157 participants. The results showed multiple respiratory viruses beyond influenza are associated with significant morbidity and mortality among adults and children in Mexico City. Detection of these agents could be useful for the adjustment of antibiotic treatment in severe cases.