As of April 30, DGE surveillance activities, focusing on patients with severe respiratory disease, had identified 97 patients with laboratory-confirmed S-OIV infection, including seven persons who had died. The first of the 97 patients reported onset of illness (any symptom) on March 17, and the most recent patients reported onset on April 26. Laboratory confirmation of S-OIV infection for the most recent 73 of these 97 cases was reported on the evening of April 29. Collection of additional information on these 73 cases is ongoing. Of the 24 patients for whom demographic and clinical information is available, 20 (83%) were hospitalized, three were examined in outpatient settings, and one had illness that was not medically attended. Patients ranged in age from <1 to 59 years, with 79% aged 5 to 59 years; 15 (62%) patients were female. Patients with confirmed S-OIV infection were identified in four states: Federal District (15 cases), Mexico State (seven), Veracruz (one), Oaxaca (one). Of the seven deaths, six occurred in Federal District, and one occurred in Oaxaca.