During flu season, hospitals report daily flu patient numbers to county public health as part of community surveillance. The object of this study was to assess the magnitude, demographics, and mechanism of influenza under-reporting by the University of California San Diego Health System and to assess frequency of presenting chief complaints of the patients in both Emergency Departments (EDs) who tested positive for influenza. This was a multicenter retrospective cohort study of patients who presented to the ED with an influenza-related chief complaint, was tested for influenza, a clinical impression of influenza or was prescribed Tamiflu between July 2019 to March 2020 at two tertiary care university hospitals in San Diego County. Influenza lab testing was ordered at the discretion of the health care provider but if ordered, these results were then included in a data set. Demographic characteristics are summarized for patients with a lab test ordered, patients with a clinical impression of influenza and patients with Tamiflu prescribed. Demographics characteristics are further summarized for patients who received a clinical impression (but not a lab test) for those with and without a Tamiflu prescription. ICD-9 codes were used to summarize diagnosis codes related to influenza. Descriptive statistics are presented. Between July 2019 and March 2020, of 9,831 patients with an influenza-related chief complaint, 581 tested positive for influenza. From December to January, there was a 150% increase in positive cases of influenza, going from 102 to 264 cases positive cases reported. Flu-like symptoms, cough and fever compromised the top 3 presenting chief complaints for patients who tested positive for influenza. Of the 9,831 patients, 121 did not receive a lab test but received a clinical impression and/or prescribed Tamiflu. The top chief complaints of those who did not receive a lab test but received clinical impression of influenza were flu like symptoms, fever, cough, and shortness of breath. Out of the 995 people that were admitted to hospital with respiratory infection only 148 (15%) were not tested for influenza whereas 252 of 573 cases that were admitted into hospital with cough were not tested for influenza. In this study 581 tested positive for influenza, 21% of assumed influenza cases were not included in the count sent to health department indicating under-reporting may have occurred. Top presenting chief complaints of those positive for influenza were consistent with CDC’s defined symptoms of influenza.