Optimal Timing of Repeat Multiplex Molecular Testing for Respiratory Viruses.

Determining whether and when multiplex nucleic acid amplification tests (NAATs) 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 tests were ordered and the time period in which results were likely to change. Results for NAATs performed on nasopharyngeal specimens and repeated within 90 days after initial testing were analyzed. Logistic regression models were used to compare time periods between tests with respect to the odds of a change in the sample result. During the study period, 21,819 nasopharyngeal specimens from 16,779 individuals were submitted. Of these, 8,807 samples (40%) were positive for at least one viral pathogen. Among this cohort, 2,583 specimens (12%) collected from 1,473 patients (9%) were repeat tests performed within 90 days after an initial test. If repeated within 90 days, 71% of tests (1,833 tests) did not have a change in result. Initially negative tests typically remained negative, whereas initially positive tests mostly remained positive until 11 to 15 days. The odds of result change plateaued after 20 days. The odds of result change for tests repeated within 20 days were only 0.52 times the odds (95% confidence interval, 0.43 to 0.62) for those repeated at 21 to 90 days (P < 0.001). Multiplex tests 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.