Diagnosis of RSV Infection: Adults Are Not Just Large Children
Abstract & Commentary
Synopsis: The Binax NOW chromatographic assay was found to be the optimal method for detection of RSV in upper respiratory secretions of children, while DFA testing was optimal in adults.
Source: Ohm-Smith MJ, et al. Evaluation of the Binax NOW, BD Directigen, and BD Directigen EZ assays for detection of respiratory syncytial virus. J Clin Microbiol. 2004;42: 2996-2999.
Ohm-Smith and colleagues at San Francisco General Hospital evaluated 4 assays for the detection of RSV in nasal and/or nasopharyngeal wash, aspirate, or swab specimens from adults and children with suspected viral respiratory infection during the 2002-2003 respiratory illness season. The results were compared to those obtained by cell culture.
All 180 specimens were examined by direct fluorescent antibody (DFA) testing, BD Directigen RSV EIA (D-RSV), and cell culture. Eighty-eight were also tested by the BD Directigen EZ, and 118 by the Binax NOW chromatographic assays. Fifty-three (29%) of the 180 specimens were obtained from adults. Of the 180 specimens, 26% were culture positive for RSV, including 34% of those collected from children and 8% from adults.
Of 149 samples that contained an adequate number of cells, there was agreement between DFA and culture in 96%. The overall sensitivity of DFA was 93%, while those of the NOW, EZ, and D-RSV assays were 89%, 59%, and 77%, respectively. The specificities of the assays were 97%, 100%, 98%, and 96%, respectively.
The results obtained with the assays were all comparable when applied to samples obtained from children, with the NOW assay being the most sensitive and specific. With samples from adults, however, DFA was the only effective test among those evaluated (see Figure, below).
Comment by Stan Deresinski, MD, FACP
The diagnosis of RSV infection is important for epidemiologic and clinical reasons. Hospitalized patients require adequate isolation and, although only selected high patients are candidates for antiviral therapy, a confirmed diagnosis allows the avoidance of unnecessary antibacterial therapy in others.
This study found that the rapid assays performed well in children, but that the NOW assay provided optimal results in this patient group. In stark contrast, only the DFA provided useful results in adults. Unfortunately, DFA, in contrast to the other rapid methods studied, is more labor intensive and requires highly trained technologists—individuals in short supply, especially in "off hours." Furthermore, a recent study found that DFA had a sensitivity of only 23% in adults with RSV infection.1 That investigation differed, however, from the one reviewed here, in that the "gold standard" was either a positive culture, serology, or PCR, while the current one relied only on culture. Nonetheless, the current guidelines of the Infectious Disease Society of America, for the management of immunocompetent adults with community acquired pneumonia, state "Respiratory syncytial virus (RSV) antigen detection tests are readily available but are insensitive for detecting infections in adults and are not generally recommended for adults."2
Ohm-Smith and colleagues agree that while the Binax NOW assay appears to be optimal for use in children, none of the rapid kit assays other, than DFA, were useful in adults. Their data does, however, suggest that DFA, does in fact, have value in adults for whom they suggest a 2-step procedure: "Laboratories should consider performing direct immunofluorescence and/or culture testing of specimens from adults that give negative results with any of the rapid kit tests."
1. Casiano-Colon AE, et al. Lack of Sensitivity of Rapid Antigen Tests for the Diagnosis of Respiratory Syncytial Virus Infection in Adults. J Clin Virol. 2003; 28:169-174.
2. Mandell LA, et al. Updated Practice Guidelines for the Management of Community-Acquired Pneumonia in Immunocompetent Adults. Clin Infect Dis. 2003;37: 1405-1433.
Stan Deresinski, MD, FACP, Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, is Editor of Infectious Disease Alert.