National Prevalence of Influenza Diagnoses and Vaccination Rates Among Patients Presenting to United States Physician Offices and Hospital Outpatient Departments, 2009 to 2016.

BACKGROUND: Influenza health resource utilization studies are important to inform future public health policies and prevent outbreaks. This study aimed to describe influenza prevalence, vaccination, and treatment among outpatients in the United States and to evaluate population-level characteristics associated with influenza health resource utilization. METHODS: Data were extracted from the National Ambulatory and National Hospital Ambulatory Medical Care Surveys (2009 to 2016). Prevalence rates were described as influenza visits (defined by International Classification of Diseases, Ninth Revision, Clinical Modification or International Classification of Diseases, Tenth Revision code) per 1000 total visits overall and by flu year, month, region, race, and age group. Influenza vaccination and antiviral treatments were identified by Multum code(s) and presented as vaccination visits per 1000 total visits and the percentage of patients diagnosed with influenza receiving antiviral treatment. RESULTS: In more than 19.2 million patient visits, an influenza diagnosis was made with rates ranging from 1.2 per 1000 during 2014-2015 to 3.7 per 1000 during 2009-2010. Rates were highest in the South (3.6 per 1000), in December (5.2), among black patients (2.8), and those less than 18 years (6.8). Vaccination rates were highest during 2014-2015 (29.3 per 1000) and lowest during 2011-2012 (15.5 per 1000), in the West (23.4), in October (69.2), among "other race" patients (26.2), and age less than 18 years (51.4). Overall, 39.4% of patients with an influenza diagnosis received an antiviral. CONCLUSIONS: Overall, there were no major changes in influenza diagnosis or vaccination rates. Patient populations with lower vaccination rates had higher influenza diagnosis rates. Future campaigns should promote influenza vaccinations particularly in underserved populations.