Discrepancies Between Self-Reported and High-Precision UWB-Measured Close Contacts: Evidence from a Japanese Junior High School

BackgroundAccurate identification of close contacts is essential for effective infection control. However, school-based contact tracing typically relies on retrospective self-reports, which are prone to recall bias. Ultra-wideband (UWB) indoor positioning offers centimeter-level spatial resolution but has rarely been applied in educational settings. This study is the first to benchmark self-reported "close contacts" against centimeter-level ultra-wideband (UWB) positioning in a real classroom over multiple consecutive days, extending beyond prior RFID- or Bluetooth-based school studies. MethodsWe conducted a five-day observational study in a junior high school classroom in Japan (36 participants; 33 with complete questionnaire and UWB data). Close contacts were identified via self-reported questionnaires and UWB positioning under multiple distance-time thresholds, with 1.0 meter for [≥]15 minutes as the official baseline. Discrepancies were quantified using participant-level consistency rates, and sensitivity analyses evaluated alternative thresholds. FindingsDiscrepancies between the two methods were consistently large under the 1.0 m/15 min definition. The median discrepancy was -0.16, indicating systematic overreporting in questionnaires. The smallest discrepancies occurred at 1.5 m for [≥]10 min, where UWB and recall most closely aligned. Notably, UWB continued to identify new unique contacts throughout the week, whereas questionnaire-based reporting plateaued after three days. Higher confidence in self-reports was paradoxically associated with greater overreporting. Teacher-student reciprocity was absent, despite the teacher reporting contact with all students. InterpretationIn a fixed-seating classroom, self-reported and UWB-measured close contacts diverged substantially. By leveraging centimeter-precision UWB tracking and threshold calibration, our study provides the first empirical evidence that current operational definitions reflect memory alignment more than actual spatial interactions. Incorporating UWB positioning and empirically optimized criteria may improve the accuracy and feasibility of contact tracing in schools, while minimizing unnecessary quarantines and educational disruption. FundingJapan Society for the Promotion of Science Research in contextO_ST_ABSEvidence before this studyC_ST_ABSWe searched PubMed and Google Scholar from Jan 1, 2000, to July 31, 2025, using the terms "close contact", "self-report", "recall bias", "school", "Bluetooth", "RFID", and "ultra-wideband (UWB)". Previous school-based studies relied on diaries, Bluetooth, or RFID sensors, which provide only meter-level accuracy and showed large discrepancies between reported and measured contacts. To our knowledge, no study had systematically applied UWB, with centimeter-level precision, to evaluate close contacts in a real-world classroom setting. Added value of this studyTo our knowledge, this is the first study to compare self-reported close contacts with UWB-measured proximity in a junior high school classroom over five consecutive days. We show that self-reports consistently overestimated the number of close contacts compared with UWB, that recall plateaued after three days, and that the smallest discrepancies were observed under a threshold of 1.5 m for [≥]10 min rather than the official 1.0 m for [≥]15 min definition. These findings demonstrate that operational definitions align more with recall patterns than with actual spatial interactions. Implications of all the available evidenceOur findings suggest that current close contact definitions may lead to substantial misclassification in school settings, resulting in unnecessary quarantines and educational disruption. Incorporating UWB or similar high-precision positioning technologies, together with empirically optimized thresholds, could improve the accuracy and feasibility of school-based contact tracing and help balance infection control with educational continuity.