Infectious Disease · Medical Literature
COVID-19 cluster outbreaks and infection control measures in nursing homes in Okinawa: protocol for a retrospective observational study
Abstract
Introduction Following the reclassification of COVID-19 as a category V infectious disease in Japan in May 2023, systematic public health monitoring of case numbers and cluster outbreaks was discontinued. Consequently, infection control measures, responses to cluster outbreaks and vaccination coverage in long-term care facilities were largely left to the discretion of individual facilities, and the understanding of the current situation in these settings remains insufficient. This observational study aims to retrospectively investigate COVID-19 cluster outbreaks and the resulting burdens experienced by facilities after reclassification, focusing on special nursing homes (Tokubetsu Yogo Rojin Home) for older adults, a population at particularly high risk for COVID-19-associated hospitalisation and mortality. By comprehensively evaluating facility and resident characteristics, vaccination coverage and infection prevention and control measures, this study seeks to generate evidence to inform future infection control strategies in long-term care facilities. Methods and analysis This retrospective observational study targets special nursing homes in Okinawa Prefecture and residents living in these facilities. Data for a target sample of nine nursing homes with approximately 900 residents will be collected from existing facility and medical records using the Research Electronic Data Capture system. The study was initiated in June 2025 and completion is anticipated by March 2027. The primary outcomes are the occurrence of COVID-19 cluster outbreaks in nursing homes between May 2023 and August 2025 and the facility-level burden experienced during outbreaks, including operational and economic impacts. A cluster outbreak is defined as the occurrence of ≥2 cases of the same infectious disease within a 10-day period. Key variables of interest include baseline characteristics of facilities and residents, vaccination coverage among staff and residents and infection prevention
Clinical relevance
Following Japan's reclassification of COVID-19 to a Category V infectious disease in May 2023, centralized public health surveillance of cluster outbreaks in long-term care facilities (LTCFs) was discontinued, creating a critical evidence gap in a high-risk setting. Special nursing homes (Tokubetsu Yogo Rojin Home) house older adults who remain disproportionately vulnerable to COVID-19-associated hospitalization and mortality, yet infection control decisions are now largely facility-driven without standardized oversight. This study is timely because the absence of systematic monitoring means vaccination coverage, outbreak frequency, and operational burdens in Japanese LTCFs are currently poorly characterized, limiting evidence-based policymaking.
Key findings
1. Study design: Retrospective observational study targeting nine special nursing homes in Okinawa Prefecture, with an approximate total resident sample of 900, using data captured via the Research Electronic Data Capture (REDCap) system. 2. Surveillance gap quantified: Systematic public health monitoring of COVID-19 cluster outbreaks in LTCFs was formally discontinued following Category V reclassification in May 2023, leaving facility-level data collection ad hoc and heterogeneous. 3. Primary outcome definition: A COVID-19 cluster outbreak is operationally defined as ≥2 cases of the same infectious disease occurring within a 10-day period — a threshold that will standardize outbreak identification across participating facilities. 4. Primary outcomes assessed: Occurrence of COVID-19 cluster outbreaks between May 2023 and August 2025, and facility-level burden during outbreaks encompassing both operational and economic impacts. 5. Key covariates under investigation: Baseline facility and resident characteristics, vaccination coverage among both residents and staff, and specific infection prevention and control (IPC) measures implemented at the facility level. 6. Temporal scope and status: Study initiation was June 2025 with anticipated completion by March 2027; as a protocol publication, no outcome or effect-size data are yet available.
Practice implications
Clinicians and LTCF administrators should recognize that, in the absence of mandated national surveillance post-reclassification, individual facilities bear full responsibility for IPC decision-making, underscoring the urgency of maintaining robust internal vaccination tracking and outbreak-response protocols for both residents and staff. Once findings are published, this study's standardized cluster definition (≥2 cases within 10 days) and its evaluation of vaccination coverage thresholds may provide actionable benchmarks for outbreak prevention and triggering enhanced IPC responses in similar LTCF settings. Specialists advising nursing homes should proactively audit current IPC frameworks and staff/resident booster uptake now, rather than awaiting regulatory mandates, given the demonstrated operational and economic burden that cluster outbreaks impose on these facilities.