Respiratory syncytial virus (RSV) infection has long been associated with acute respiratory illness in children and a significant cause of hospitalization of infants less than 1 year of age worldwide. Recently, studies have also elucidated the clinical impact of RSV infections in adult populations, with the risk of serious infection increasing with age (Falsey).
RSV is a common cause of acute respiratory illness as well as exacerbation of underlying medical conditions in older adults. RSV is second only to influenza (Collins) as a cause of medically significant respiratory tract illnesses in adult populations and is estimated to cause 177,000 hospitalizations and 14,000 annual deaths in U.S. adults age 65 years and older. Moreover, the annual cost of RSV-related illness in this age group is estimated at almost $103 million (Gessner). Based on estimates for increased life expectancy and a progressively aging population, costs are destined to rise. Despite growing knowledge on its disease burden, RSV infections in adults are frequently under recognized in clinical settings, and tests that specifically target RSV may not be requested or are substantially delayed. With the growth in awareness of the impact of RSV infections in the elderly, testing for RSV in elderly with acute respiratory infection will become increasingly important for the effective management of these patients. This need for testing will become essential with the anticipated advent of RSV-specific antiviral treatments (Behzadi) for this dangerous viral illness.
Because RSV circulates along with many other winter respiratory viruses, differential diagnosis becomes a critical component in the effective management of high-risk adult patients. Notably, RSV and influenza A infections in adults are largely indistinguishable based on clinical presentation (Walsh) alone. In fact, a recent study demonstrated nearly 90% of all RSV-infected adults (Falsey) exhibit some combination of acute respiratory symptoms common to influenza A. Moreover, adults hospitalized with either influenza or RSV are typically admitted under a wide range of similar diagnoses (Falsey) including pneumonia, acute exacerbation of chronic obstructive pulmonary disease (COPD), congestive heart failure, asthma, bronchitis, and myocardial infarction. Outcomes for hospitalized patients who have tested positive for influenza or RSV, respectively, are also similar, with 8% mortality (Falsey) observed in both groups.
Conversely, however, patients with RSV do not seek medical attention as quickly and experience a longer time from symptom onset to hospitalization (Sundaram) compared to patients with similar clinical presentations and influenza infection. The slower symptom onset and lower fever associated with RSV likely drives these patients to seek medical care later than patients with influenza. Viral shedding starts soon after infection in adults and peaks at about day three, followed by a two- to three-day plateau and then a steady decline. Adults age 65 years and older tend to shed slightly higher titers (Walsh) than younger adults and for a longer duration.
Traditionally, testing for RSV in adult populations was not performed routinely in outpatient settings primarily due to the lack of awareness regarding the impact of RSV in older adults. However, a growing interest in syndromic surveillance, along with the development of highly sensitive rapid antigen tests (RADT) and molecular diagnostic tools for use at the point-of-care has allowed for faster, more accurate identification of respiratory infections and implementation of appropriate clinical care.