Rapid antigen testing for respiratory virus syncytial can be used in neonates with provisos

Article Outline

• Question
• Design
• Setting
• Participants
• Outcomes
• Main Results
• Conclusions
• Commentary
• Copyright

Yen AB, Demmler-Harrison GJ. Rapid antigen testing to detect respiratory syncytial virus performs well in neonates. Pediatr Infect Disease J 2011;30:234-7.

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Question 

In neonates with suspected respiratory syncytial virus (RSV) infection, how accurate is the RSV rapid antigen test?

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Design 

Retrospective analysis (1997-2008) of rapid RSV antigen testing in neonates (≤30 days) using a laboratory database of the Diagnostic Virology Laboratory.

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Setting 

Texas Children's Hospital, Houston, Texas.

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Participants 

3691 respiratory samples collected consecutively were included. Of these, 784 (21%) were positive for RSV by rapid test and 402 (10.9%) showed growth of RSV in viral culture.

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Outcomes 

Sensitivity and specificity were calculated using viral culture as the reference standard.

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Main Results 

Overall sensitivity was 90.3% and specificity was 88.2% (likelihood ratio [LR] for a positive rapid test [LR+] = 7.7 and LR for a negative rapid test [LR-] = 0.11). Sensitivity was lower in nonseason samples (76.5% vs. 90.9% [P = .048]), but specificity was higher in nonseason samples (95.6% vs. 87.1% [P ≤ .001]). Lower specificity was seen in samples submitted from neonates evaluated in the emergency department compared with inpatient floors, neonatal intensive care unit, and unspecified venues (85.1% vs. 95.6%, 94.3%, 95.5%, respectively P ≤ .001). Overall, there was no statistical difference in test performance based on specimen type. However, when RSV was in season, nasal washes were more sensitive than tracheal aspirates (LR- = 0.10 vs. 0.43, P = .017).

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Conclusions 

Rapid RSV antigen testing was sensitive and specific in detecting RSV infections in neonates. Moderate differences in test performance occurred in and out of RSV season, by sample type, and by the location within the hospital from where the sample was obtained.

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Commentary 

Rapid antigen tests are the most frequently used diagnostic test for RSV. This study, which examined a large number of samples collected over 11 years, demonstrates the benefits and caveats of rapid testing, such as equal proportions of true-positive and false-positive specimens. Rapid antigen tests were compared with viral isolation, which was the “platinum standard,” but now is infrequently used because of its expense and technical difficulty. The reference standard currently is usually a highly sensitive molecular assay, such as polymerase chain reaction, which would result in sensitivities and specificities considerably different from those in this study. However, because these data indicate that rapid antigen tests perform equally well among neonates as among older children, the same should be true when a molecular standard is used. Among older children, the accuracy of the rapid tests when compared with molecular assays is highly variable. In part, this results from the quality of the specimen and the yearly variability among the available rapid detection kits, as shown in this paper. Furthermore, these rapid assays should be used during the peak period of RSV activity. Before and after the peak season, when the incidence of disease is less, the sensitivity and specificity of rapid tests are low, and the positive predictive value decreases. Thus, in summary, the major benefit of this paper is that it can provide guidance to the wise use of the currently most frequently used diagnostic assay for RSV.