Patterns of seasonal influenza activity in U.S. core-based statistical areas, described using prescriptions of oseltamivir in Medicare claims data

Abstract

Using Medicare claims data on prescriptions of oseltamivir dispensed to people 65 years old and older, we present a descriptive analysis of patterns of influenza activity in the United States for 579 core based statistical areas (CBSAs) from the 2010-2011 through the 2015-2016 influenza seasons. During this time, 1,010,819 beneficiaries received a prescription of oseltamivir, ranging from 45,888 in 2011-2012 to 380,745 in 2014-2015. For each season, the peak weekly number of prescriptions correlated with the total number of prescriptions (Pearson's r ≥ 0.88). The variance in peak timing decreased with increasing severity (p < 0.0001). Among these 579 CBSAs, neither peak timing, nor relative timing, nor severity of influenza seasons showed evidence of spatial autocorrelation (0.02 ≤ Moran's I ≤ 0.23). After aggregating data to the state level, agreement between the seasonal severity at the CBSA level and the state level was fair (median Cohen's weighted κ = 0.32, interquartile range = 0.26-0.39). Based on seasonal severity, relative timing, and geographic place, we used hierarchical agglomerative clustering to join CBSAs into influenza zones for each season. Seasonal maps of influenza zones showed no obvious patterns that might assist in predicting influenza zones for future seasons. Because of the large number of prescriptions, these data may be especially useful for characterizing influenza activity and geographic distribution during low severity seasons, when other data sources measuring influenza activity are likely to be sparse.

Differences in epidemic spread patterns of norovirus and influenza seasons of Germany: an application of optical flow analysis in epidemiology

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Estimating the Incidence of Influenza at the State Level — Utah, 2016–17 and 2017–18 Influenza Seasons

“…The Utah Department of Health and the Salt Lake County Health Department used these methods to synthesize influenza surveillance data, and the Salt Lake County Health Department published weekly estimates of state-level influenza burden during the 2018–19 and current influenza seasons ( 8 ). These timely subnational estimates at the state and county levels are valuable for providing a local understanding of influenza activity given the geographic variation in influenza activity in the United States ( 3 ).…”

“…Since the 2009 influenza pandemic, CDC has estimated the burden of influenza in the United States each year ( 1 , 2 ). However, influenza activity can vary widely across the country, making the use of national burden estimates difficult for state or county public health messaging, planning, and responses ( 3 ). The 2017–18 influenza season was one of high severity, with an estimated 45 million illnesses, 21 million medically attended illnesses, 810,000 hospitalizations, and 61,000 deaths occurring throughout the United States ( 1 ).…”

Notes from the Field: Assessment of State-Level Influenza Season Severity — Minnesota and Utah, 2017–18 Influenza Season

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