# Determinants of COVID-19 outbreak size in elderly residential facilities in Okinawa Prefecture, Japan, April to June 2022

## TL;DR

This study analyzed 127 COVID-19 outbreaks in elderly care facilities in Okinawa and found that contact-based testing and resident mask-wearing reduced outbreak sizes.

## Contribution

The study identifies effective infection control strategies in elderly care facilities, showing contact-based testing is more effective than routine screening.

## Key findings

- Contact-based testing reduced outbreak size compared to routine RT-PCR screening (aRR 0.11).
- Resident mask-wearing was linked to smaller outbreaks (aRR 0.40).
- Routine RT-PCR screening detected only 16.7% of staff index cases.

## Abstract

•Overall, 127 COVID-19 outbreaks from 78 elderly care facilities in Okinawa were analyzed.•Contact-based testing (staff) outperformed routine staff reverse transcription polymerase chain reaction (RT-PCR) screening (adjusted relative risk [aRR] 0.11).•Resident mask-wearing was associated with smaller outbreak size (aRR 0.40).•Routine staff RT-PCR screening detected only 16.7% of staff index cases.•Proximity-sensing tools may improve exposure identification and targeted testing.

Overall, 127 COVID-19 outbreaks from 78 elderly care facilities in Okinawa were analyzed.

Contact-based testing (staff) outperformed routine staff reverse transcription polymerase chain reaction (RT-PCR) screening (adjusted relative risk [aRR] 0.11).

Resident mask-wearing was associated with smaller outbreak size (aRR 0.40).

Routine staff RT-PCR screening detected only 16.7% of staff index cases.

Proximity-sensing tools may improve exposure identification and targeted testing.

: COVID-19 outbreaks in residential facilities for the elderly can have severe consequences; however, effective preventive strategies remain under-evaluated. This study aimed to identify actionable, facility-level factors associated with outbreak size in such facilities in Okinawa, Japan.

: We conducted a questionnaire-based cross-sectional study of 78 residential facilities for the elderly that experienced confirmed COVID-19 outbreaks between April and June 2022. Facility-level data on infection-control practices, outbreak characteristics, and staff testing approaches were analyzed using negative binomial regression models to quantify factors associated with outbreak size.

: Outbreaks detected via contact-based testing of staff were significantly smaller than those detected through routine staff reverse transcription polymerase chain reaction screening (adjusted relative risk [aRR]: 0.11; 95% confidence interval [CI]: 0.03-0.37). Resident mask-wearing was associated with smaller outbreak sizes (aRR: 0.40; 95% CI: 0.16-0.99). Routine screening identified only 16.7% of staff index cases despite being widely implemented, suggesting limitations in effectiveness.

: Risk-based, exposure-driven testing appears markedly more effective than fixed-interval screening for limiting outbreak size in residential facilities for the elderly. Implementation should consider both operational feasibility and support systems for frontline staff.