# Risk Factors for COVID-19 Cluster Infection in Hospitalized Patients

## TL;DR

This study identifies healthcare worker infections as a key risk factor for hospital-based COVID-19 clusters in Japan during the seventh and eighth waves.

## Contribution

The study reveals that infections originating from healthcare workers are independently associated with cluster development in hospitalized patients.

## Key findings

- A total of 40 infection events were observed, with 17 developing into clusters.
- Infections originating from healthcare workers were independently linked to cluster formation.
- Household transmission is a common source of SARS-CoV-2 infections among healthcare workers.

## Abstract

Introduction

In Japan, in the seventh wave of coronavirus disease 2019 (COVID-19) from July 2022 to September 2022, followed by the eighth wave of COVID-19 from November 2022 to January 2023, nosocomial clusters became more frequent in many healthcare facilities. If a cluster occurs in a hospital, the restrictions on general healthcare and the impact on hospital management, as well as the impact on community healthcare, are enormous. We analyzed the risk factors for COVID-19 cluster infection in hospitalized patients.

Methods

We retrospectively collected cases of COVID-19 infection among hospitalized patients in the seventh and eighth waves. The occurrence of a COVID-19 patient in a hospitalized patient was defined as one event.

Results

A total of 40 events were observed in the seventh and eighth waves. There were 17 events that developed into clusters. The following factors showed a significant association with cluster infection in a univariate analysis: “seventh wave,” “originated from healthcare worker,” and “initial examination according to contact list.” The multivariate analysis revealed that “originated from healthcare worker” was independently associated with cluster infection.

Conclusion

Preventing the development of COVID-19 clusters is very important for nosocomial infection control. Our study suggests that COVID-19 infection in a healthcare worker is a risk factor for the development of a cluster. When healthcare workers are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it is often due to household transmission. Measures against household transmissions are important to prevent infection among healthcare workers.