Viruses Associated With Acute Respiratory Infections and Influenza-like Illness Among Outpatients From the Influenza Incidence Surveillance Project, 2010–2011

Fowlkes, Ashley; Giorgi, Andrea; Erdman, Dean; Temte, Jon; Goodin, Kate; Di Lonardo, Steve; Sun, Yumei; Martin, Karen; Feist, Michelle; Linz, Rachel; Boulton, Rachelle; Bancroft, Elizabeth; McHugh, Lisa; Lojo, Jose; Filbert, Kimberly; Finelli, Lyn

BACKGROUND: The Influenza Incidence Surveillance Project (IISP) monitored outpatient acute respiratory infection (ARI; defined as the presence of ≥2 respiratory symptoms not meeting ILI criteria) and influenza-like illness (ILI) to determine the incidence and contribution of associated viral etiologies. METHODS: From August 2010 through July 2011, 57 outpatient healthcare providers in 12 US sites reported weekly the number of visits for ILI and ARI and collected respiratory specimens on a subset for viral testing. The incidence was estimated using the number of patients in the practice as the denominator, and the virus-specific incidence of clinic visits was extrapolated from the proportion of patients testing positive. RESULTS: The age-adjusted cumulative incidence of outpatient visits for ARI and ILI combined was 95/1000 persons, with a viral etiology identified in 58% of specimens. Most frequently detected were rhinoviruses/enteroviruses (RV/EV) (21%) and influenza viruses (21%); the resulting extrapolated incidence of outpatient visits was 20 and 19/1000 persons respectively. The incidence of influenza virus-associated clinic visits was highest among patients aged 2–17 years, whereas other viruses had varied patterns among age groups. CONCLUSIONS: The IISP provides a unique opportunity to estimate the outpatient respiratory illness burden by etiology. Influenza virus infection and RV/EV infection(s) represent a substantial burden of respiratory disease in the US outpatient setting, particularly among children.