Table 1 Definition of COVID-19 according to the source of infection and nosocomial outbreak criteria

Community-associated COVID-19 (CA-COVID-19)

(a) Symptoms present on admission or with onset on day 1 or 2 after admission

(b) Symptom onset on day 3–7 and a strong suspicion of community transmission

Indeterminate association (IA-COVID-19)

Symptom onset on day 3–7 after admission, with insufficient information regarding the source of infection to assign to another category

Probable healthcare-associated COVID-19 (HA-COVID-19)

(a) Symptom onset on day 8–14 after admission

(b) Symptom onset on day 3–7 and a strong suspicion of healthcare transmission

Definite healthcare-associated COVID-19 (HA-COVID-19)

Symptom onset on day > 14 after admission

SARS-CoV-2-related hospital outbreak

Two or more test-confirmed COVID-19 cases among hospitalized patients with (a) illness onset after at least 8 days after hospital admission (for at least one of the cases) and (b) establishment of an epidemiological link between the cases (exposure event)