Background
Accurate 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.
Methods
We 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.
Findings Discrepancies 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.
Interpretation In 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.
Funding Japan Society for the Promotion of Science
Evidence before this study We 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 study To 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 evidence Our 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.
Competing Interest Statement
The authors have declared no competing interest.
Funding Statement
KM acknowledges support from the Japan Society for the Promotion of Science (JSPS) KAKENHI [Grant 20H03940 and 20KK0367].The funding source had no role in study design, data collection, data analysis, interpretation, writing of the manuscript, or the decision to submit for publication. All authors had full access to the data in the study and accept responsibility for the decision to submit for publication.
Author Declarations
I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.
Yes
The details of the IRB/oversight body that provided approval or exemption for the research described are given below:
The study protocol was reviewed and approved by the Ethics Committee of Kyoto University Graduate School of Medicine (Approval No. R6-G-8-2).
I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.
Yes
I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).
Yes
I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.
Yes
Data sharing
The individual-level UWB positioning data and questionnaire responses contain potentially identifiable information and will be used in ongoing graduate student research projects, including network analyses. For this reason, the full dataset cannot be shared publicly at this time. Deidentified summary statistics and analytic code supporting the findings of this article will be made available from the corresponding author upon publication. The full deidentified dataset will be deposited in a public repository within 2 years of publication. All authors had full access to the data and accept responsibility for the decision to submit for publication.