Is the interpretation of rapid antigen testing for respiratory syncytial virus as simple as positive or negative?

OBJECTIVE: To measure the performance characteristics of an immunochromatographic rapid antigen test for respiratory syncytial virus (RSV) and determine how its interpretation should be contextualised in patients presenting to the emergency department (ED) with bronchiolitis. DESIGN: Diagnostic accuracy study of a rapid RSV test. SETTING: County hospital ED. INTERVENTION: We took paired nasal samples from consecutively enrolled infants with bronchiolitis and tested them with a rapid immunochromatographic antigen test and reverse transcriptase PCR gold standard. OUTCOME MEASURES: Sensitivity, specificity, the effect of point prevalence, clinical findings and overall context on predictive values. We used these to construct a graphical contextual model to show how the results of RSV antigen tests from infants presenting within 24 h should influence interpretation of subsequent antigen tests. RESULTS: We analysed 607 patients. The sensitivity and specificity for immunochromatographic testing was 79.4% (95% CI 73.9% to 84.2%) and 67.1% (95% CI 61.9% to 72%) respectively. We found little evidence of spectrum bias. In our contextual model the best predictor of a positive RT-PCR test was a positive antigen test OR 5.47 (95% CI 3.65 to 8.18) and the number of other infants having positive tests within 24 h OR 1.48 (95% CI 1.26 to 1.72) per infant. Increasing numbers presenting to the ED with bronchiolitis in a given day increases the probability of RSV infection. CONCLUSIONS: The RSV antigen test we examined had modest performance characteristics. The results of the antigen test should be interpreted in the context of the results of previous tests.

Prevalence of Bordetella pertussis and Bordetella parapertussis in infants presenting to the emergency department with bronchiolitis.

BACKGROUND: The clinical presentation of Bordetella pertussis can overlap with that of respiratory syncytial virus (RSV), and coinfection does occur, but management differs. HYPOTHESIS: The prevalence of B. pertussis is < 2% among Emergency Department (ED) patients with bronchiolitis. Our secondary hypothesis was that the prevalence of Bordetella parapertussis is also < 2% among these patients. METHODS: Nasal washings were obtained from children up to 18 months of age (inclusive) who presented to a county hospital ED with a clinical diagnosis of bronchiolitis. These washings were frozen to -70°C before testing for B. pertussis and B. parapertussis using species-specific real-time polymerase chain reaction (PCR) assays. The assays were optimized to target conserved regions within a complement gene and the CarB gene, respectively. A Bordetella spp. genus-specific real-time PCR assay was designed to detect the Bhur gene of B. pertussis, B. parapertussis, and B. bronchiseptica. RSV antigen detection was also performed. RESULTS: There were 227 patients enrolled. After exclusions, 204 remained in the analysis. RSV antigen testing was positive in 109/186 (59%) of the patients in whom it was performed. All samples were tested for B. pertussis. B. parapertussis testing could not be completed on 23 samples. No cases (0/204; 95% confidence interval [CI] 0-1.8%) tested positive for B. pertussis or B. parapertussis (0/181; 95% CI 0-2%). CONCLUSION: The prevalence of B. pertussis in children presenting to the ED with bronchiolitis was < 2%.

Comparison of respiratory virus detection rates for infants and toddlers by use of flocked swabs, saline aspirates, and saline aspirates mixed in universal transport medium for room temperature storage and shipping.

A nylon flocked swab/universal transport medium collection method developed for bacterial sexually transmitted infections was adapted to detect respiratory viruses in infants and toddlers. This method significantly outperformed the traditional use of nasal aspirates in terms of PCR-based virus detection (P = 0.016), and the samples were easier for clinicians to evaluate, store, and transport.

Prevalence of Bordetella pertussis and Bordetella parapertussis in Samples Submitted for RSV Screening.

BACKGROUND: The clinical presentation of Bordetella pertussis can overlap with that of respiratory syncytial virus (RSV); however, management differs. HYPOTHESIS: First, the prevalence of B. pertussis is less than 2% among patients screened for RSV, and second the prevalence of B. parapertussis is also less than 2% among these patients. METHODS: Nasal washings submitted to a clinical laboratory for RSV screening were tested for B. pertussis and B. parapertussis, using species-specific real-time polymerase chain reaction (PCR) assays. These were optimized to target conserved regions within a complement gene and the CarB gene, respectively. A Bordetella spp. genus-specific real-time PCR assay was designed to detect the Bhur gene of B. pertussis, B. parapertussis, and B. bronchiseptica. RSV A and B subtypes were tested by reverse transcription-PCR. RESULTS: Four hundred and eighty-nine clinical samples were tested. There was insufficient material to complete testing for one B. pertussis, 10 RSV subtype A, and four RSV subtype B assays. Bordetella pertussis was detected in 3/488 (0.6%) (95% CI 0.1% to 1.8%), while B. parapertussis was detected in 5/489 (1.0%) (95% CI 0.3% to 2.4%). Dual infection of B. pertussis with RSV and of B. parapertussis with RSV occurred in two and in three cases respectively. RSV was detected by PCR in 127 (26.5%). CONCLUSION: The prevalence of B. pertussis in nasal washings submitted for RSV screening was less than 2%. The prevalence of parapertussis may be higher than 2%. RSV with B. pertussis and RSV with B. parapertussis coinfection do occur.