Winter Respiratory Viruses and Health Care Use: A Population-Based Study in the Northwest United States

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Abstract
To quantify health care use among adults during influenza and respiratory syncytial virus (RSV) seasons, we identified a cohort of veterans aged ⩾18 years who used Department of Veterans Affairs (VA) facilities in Oregon and Washington states as their source of health care. During 1998–2000, veterans accrued 237,159 person-years of follow-up. Using VA data sources, we measured acute cardiopulmonary hospitalizations and primary care and urgent care visits. Differences between rates of study events when influenza and/or RSV were circulating and event rates when neither virus was circulating were used to calculate winter virus-attributable morbidity. Inpatient and outpatient event rates were consistently higher during winter virus season, compared with non-winter virus season. Annual rates of cardiopulmonary hospitalizations attributable to influenza or RSV infection ranged from 0.8 (95% confidence interval [CI], 0.1–1.5) per 1000 low-risk individuals aged 18–49 years, to 10.6 (95% CI, 7.5–13.6) per 1000 high-risk individuals aged ⩾65 years. Each year, circulation of influenza and RSV coincide with predictable increases in medical care use.