Increase in Detection of Respiratory Syncytial Virus Among Older Adults in Arizona : An Association With Changes in Testing Practices

Objectives: Respiratory syncytial virus (RSV) is a common cause of respiratory illness, health care visits, and hospitalizations. Arizona, which began conducting laboratory surveillance in 2004, has noted an increase in RSV cases (defined as a laboratory-positive result) among adults aged ≥65, concurrent with increasing reports from polymerase chain reaction (PCR) testing. We assessed whether the shift in the age distribution of reported RSV cases resulted from a change in RSV testing practices.

Methods: We used data on laboratory-confirmed RSV cases reported during 2013-2017 from the statewide surveillance system to assess the frequency of test types (rapid antigen, immunofluorescence assay, PCR, and viral culture) by age groups across RSV seasons, and we used logistic regression to estimate changes in odds of receiving a PCR test. We used statewide emergency department hospital discharge data for the same period to assess testing practices regardless of test result.

Results: The overall proportion of PCR tests among RSV cases increased significantly, from 22% in 2013 to 55% in 2017 ( < .001). The percentage of RSV cases among adults aged ≥65 also increased significantly, from 4% in 2013 to 11% in 2017 ( < .001) of RSV cases. Adults aged ≥65 had more than 8 times the odds of positive PCR results than children aged <5, both in crude (odds ratio [OR] = 8.8; 95% CI, 7.6-10.2) and season-adjusted (adjusted OR = 8.1; 95% CI, 7.0-9.5) models. Hospital discharge data corroborated increased RSV PCR usage from 2013 to 2017.

Conclusion: Increasing RSV rates among adults aged ≥65 are likely a result of changes in testing practices. This age group may need more targeted intervention and future vaccination.