Optimal Timing of Repeat Multiplex Molecular Testing for Respiratory Viruses

Background: Determining if and when multiplex nucleic acid amplification testing (NAAT) for respiratory viruses should be repeated is difficult. We analyzed 5 years of results for a multiplex NAAT targeting 14 respiratory viruses to determine how often repeat testing is ordered and the time interval when results are likely to change. Methods: Results for NAAT performed on nasopharyngeal specimens repeated within 90 days of initial testing were analyzed. Logistic regression models were used to compare time intervals between tests on the odds of a change in sample result. Results: During the study period, 21,819 nasopharyngeal specimens were submitted from 16,779 individuals. Of these, 8,807 (40%) samples were positive for at least one viral pathogen. Among this cohort, 2,583 (12%) specimens collected from 1,473 (9%) patients were repeat tests within 90 days of an initial test. If repeated within 90 days, 71% (1833) of tests did not have a change in result. Initially negative tests typically remained negative whereas initial positive tests mostly remained positive until 11- 15 days. Odds of result change plateaued after 20 days. The odds of a change in result for tests repeated within 20 days were only 0.52 times the odds for 21-90 days (95% CI 0.43, 0.62, p Conclusions: Multiplex testing for respiratory viruses that are repeated within short periods lead to redundant results at additional costs. Repeat testing of nasopharyngeal specimens before 20 days demonstrates little change. These results provide a vital component for use in laboratory stewardship to curtail unnecessary respiratory viral testing.