Current practice and timing of rapid point-of-care testing for acute respiratory tract infections in outpatient care: a retrospective cohort study.

PURPOSE: Although acute respiratory tract infections are common in outpatient practice, the association between symptom duration and the diagnostic yield of SPOTFIRE®, a rapid multiplex assay, is unclear. We herein aimed to evaluate the current use of SPOTFIRE®, examine the association between symptom duration and test positivity, and identify factors associated with positivity. METHODS: This retrospective cohort study included patients with a fever and/or respiratory symptoms who received a SPOTFIRE® assay between June 2024 and June 2025 at a single outpatient clinic in Tokyo, Japan. The overall positivity rate and predicted probabilities of the test positivity according to the interval from symptom onset to testing were evaluated. Multivariable logistic regression was performed to detect factors associated with positivity. RESULTS: The overall positivity rate in 481 episodes was 62.0% (298/481). Cough, sputum or both were reported in 80.0% of the episodes and were the most common symptoms. Persistent or worsening symptoms were the leading indication for SPOTFIRE® (47.6%). The adjusted predicted probability declined from 71.5% on day 0 to 32.4% on day 21. Age ≤ 17 years (adjusted odds ratio [aOR]: 6.10; 95% confidence interval [CI]: 1.56-23.82), fever (aOR: 1.84; 95% CI: 1.19-2.85), and nasal symptoms (aOR: 2.89; 95% CI: 1.79-4.66) were independently associated with positivity. Each additional day from onset was associated with lower odds (aOR: 0.91; 95% CI 0.86-0.95). CONCLUSION: The positivity rate was highest soon after symptom onset and declined with increasing symptom duration. Considering the illness stage and patient characteristics when determining the timing of testing may improve the diagnostic yield of the assay.