| Human to animal |
Direct (droplets/airborne) |
Zookeepers |
Most likely |
An earlier asymptomatic infectious case among the zookeepers may have been missed. In the internal enclosures, zookeepers wearing facemasks could have come in close contact with lions or gorillas. Staffrooms were adjacent to the gorilla enclosure and connected via an open connection. |
| Human to animal |
Direct (droplets/airborne) |
Visitors |
Unlikely |
The distance between visitors and animals outside is at least 1.0 m. Indoor enclosures are fully closed (glass/wall), separating animals from visitors. For the lions, air of visitors flows via an HEPA filter through the indoor enclosure of the lions to the outside. |
| Human to animal |
Indirect (fomites) |
Zookeepers/facility staff |
Less likely |
20 facility staff members tested SARS-CoV-2 negative on 24 November 2021 and an asymptomatic infectious case among the facility staff may have been missed. One staff member did not take the test. Transmission may have occurred during cleaning of the enclosures or during food preparation. |
| Human to animal |
Indirect (fomites) |
Visitors |
Unlikely |
Visitors may have thrown, or the wind may have blown, contaminated rubbish or food leftovers into the animal exhibits. Evolving evidence about SARS-CoV-2 transmission suggests that the share of transmission of SARS-CoV-2 via fomites is small [25]. |
| Sewage |
Waterborne (faeces) or fomites |
Sewage |
Highly unlikely |
SARS-CoV-2 virus was detected in regional sewage, however, no problems with sewage (e.g. flooding of surface water nearby outside enclosures) were detected. |
| Intermediate host |
Fomites, faeces or droplets |
Other wild animals such as rodents, mustelids, bats, feral cats, squirrels, foxes etc. (1–3). |
Highly unlikely |
15 mice and rats were caught in the zoo, of which five rodents were caught in the gorilla and lion exhibits. All tested negative for SARS-CoV-2 RNA. It was impossible to reach the animal enclosures for most other (larger) wild and feral animals. |
