3.3 COVID-19 clusters/incidents definitions

The definitions below should be applied to determine if a COVID-19 cluster/incident within a healthcare setting is occurring and determine when it can end. When assessing patient and staff clusters to determine if an outbreak is occurring, a high degree of suspicion should be applied. Active surveillance should be undertaken by IPCTs to allow clusters/incidents to be detected at the earliest possible opportunity.

Note: the current COVID-19 cluster reporting system is currently under review 

3.3.1 Criteria to declare a COVID-19 cluster/incident in an inpatient setting

Two or more patient and/or staff cases of COVID-19 within a specific setting where nosocomial infection and ongoing transmission is suspected. For the purposes of this reporting, a high degree of suspicion should be applied and further investigation undertaken for any ward where there are unexpected cases of suspected or confirmed COVID-19. e.g., any cases that were not confirmed or suspected on admission. No time limit should be applied to determining whether a case is nosocomial e.g. 48 hours.


Where two or more staff cases of suspected or confirmed COVID-19 are identified and transmission between the staff members is suspected to be associated with workplace exposure/behaviours.

Note: If there is a single suspected or confirmed case in a patient who was not suspected as having COVID-19 on admission, this should initiate further investigation and risk assessment. This single case may constitute a possible cluster depending on the contacts and exposures identified. Contact tracing within acute inpatient settings should be based on local outbreak management and on the advice of the local Infection Control Doctor.

Where the patient has been in a side room with transmission-based precautions in place for 48 hours prior to symptom onset, and where all staff were wearing appropriate PPE appropriately, the IPCT may decide that there is no further action needed other than active monitoring for any new unexplained cases associated with the ward.

3.3.2 Criteria to determine that a COVID-19 cluster/incident in an inpatient setting has ended

No new test-confirmed or suspected cases with illness onset date 10 days following the last new confirmed case (from date of symptom onset or date of positive test if case has remained asymptomatic), within the affected ward or department.  The cluster can be closed provided that these criteria are met.