1419 - National ambulatory health resource utilization and geographic disparities of influenza in the United States, 2009 to 2016

Background: Influenza can affect up to 10% of adults and 30% of children and, in specific populations, can lead to severe illness and death. Although epidemiological surveillance on influenza patterns have been expanded since 2009, it is also imperative to observe specific trends for influenza immunization and treatment to inform and potentially prevent future outbreaks. The primary objective of this study was to describe influenza prevalence, immunization, and treatment among outpatients in the United States (US).

Methods: This was a cross-sectional study using the Centers for Disease Control and Prevention’s National Ambulatory and Hospital Ambulatory Medical Care Surveys from 2009 to 2016. All patient visits were eligible for inclusion, and prevalence rates were described as influenza visits per 1,000 patient visits. Patient visits were categorized by year, month, and US geographic region. Influenza vaccinations and treatments were defined by their respective Multum code(s) and diagnosis was identified using International Classification of Diseases, 9^th Revision, Clinical Modification (ICD-9-CM) and ICD-10 codes for the appropriate survey years. Data were presented descriptively.

Results: Over 7 billion visits were included for analysis. Overall, influenza rates varied over the study period with the highest rate in 2009 (5.0) and lowest in 2015 (0.9). Immunization rates were highest in 2014 (25.4) and lowest in 2016 (12.5). The South had the highest influenza rates (3.6) and proportion of influenza visits that included treatment (45.6%), as well as the lowest immunization rates (17.6). The Northeast had the lowest influenza rate (1.5), while the West had the lowest proportion of influenza treatment (24.9%) and highest immunization rates (23.4). December and February had the highest rates of influenza (5.2 and 5.7, respectively), while rates of immunization were the highest in September and October (48.9 and 71.7, respectively).

Conclusion: Immunization rates were highest in the fall months and influenza rates were highest in the winter months. Overall, this study found that regions with lower influenza vaccination had higher influenza rates, and vice versa. Future campaigns should promote immunizations against the influenza virus particularly in underserved regions (e.g., South).