Influenza surveillance in community-dwelling elderly compared with children

BACKGROUND: Acute respiratory illnesses (ARIs) are the leading cause of medical visits for community-dwelling patients of all ages, but virologic and clinical descriptions of these illnesses in older adults are infrequent. OBJECTIVES: To determine the feasibility of influenza surveillance in a population of community-dwelling elderly, to compare the patterns of influenza infection in elderly persons with that observed in young populations in which surveillance is usually conducted, and to describe the clinical presentation of influenza infection in elderly outpatients who seek medical attention for ARI. DESIGN: Prospective clinical and viral surveillance of ARIs among ambulatory patients during 3 consecutive winter seasons. SETTING: Nine internal medicine and 3 pediatric practices in Upstate New York in cooperation with the Medicare Influenza Vaccine Demonstration Project. PATIENTS: Elderly (n=808) and pediatric (n=2080) outpatients with ARI office visits. MEASUREMENTS: Frequency of influenza and other respiratory virus isolates and clinical profile of influenza among older adults and children with ARIs. RESULTS: Influenza virus was the viral agent recovered most often from specimens obtained from patients in both age groups with ARI symptoms, especially those with fever. Influenza accounted for 11% of ARIs in adults (87 isolates) and 20% in children (408 isolates). At the initial illness visit, influenza infection was equally common in elderly individuals with or without underlying cardiopulmonary conditions. Lower respiratory tract signs occurred in 13% of the adults and in 7% of the children with influenza documented by laboratory studies. Other respiratory viruses were recovered from specimens obtained from 20 adults and from 259 children. CONCLUSIONS: Viruses are important agents of ARIs in elderly outpatients. Children and older adults experience similar patterns of influenza infection and other epidemic respiratory pathogens, such as parainfluenza and respiratory syncytial viruses. Viral identification is feasible in older adults seen in physicians' offices and may contribute to improved measures of effects of influenza and other respiratory viruses on ARIs.