An apparently unlinked COVID-19 case was announced late last week in Brisbane, setting off warning bells that there was an untracked transmission within the community.
We learned a 26-year-old male had been symptomatic since March 22. He only went for testing on the 25th, but had isolated since the 22nd. Venues he visited were quickly identified and people who had visited these possible exposure sites in the specified time periods were asked to get a test and isolate until they received a negative result.
Other measures were quickly put in place – from midday on March 26, hospitals and disability and aged care were closed to visitors in Brisbane and Moreton. Masks were made mandatory and vulnerable cohorts encouraged to stay home until the authorities knew what is going on. The first case was a landscaper and so mostly works outside, and the health authorities were reassured this posed a lower transmission risk.
Genome sequencing results came through the next day. The good news was the virus responsible for this latest infection matched to another known recent case – the doctor who tested positive after treating a positive returned traveller on March 9 at the Princess Alexandra Hospital in Brisbane. But with that news also came confirmation that this case had the more infectious B1.1.7 variant of concern that originally emerged in the UK.
“If we can find the first case and not the 40th in a cluster, then we can get on top of it”, was the reassuring message from the Queensland Premier Annastacia Palaszczuk when the first case in this cluster was announced on Friday. However it was quite clear this was not the index case, and we still cannot be sure how many community cases preceded it.
Even with the variant genomically tied to the strain responsible for the hospital transmission, there are still up to seven or eight days between that event and the time this known local case was probably exposed. Given the 26-year-old is not a traveller and not linked to hotel quarantine or the hospital, this could still mean one or two intermediary cases, and also signals the possibility of additional transmissions chains.
It is a bit reminiscent of the Avalon outbreak in NSW where a matching variant was never found in hotel quarantine, and upstream searches failed to identify the source. Arguably the most likely route into the community then was cabin crew from international flights as they were not routinely tested back then. Because of this uncertainty, however, there was no way of knowing how long the community transmission had been running before the virus became visible in the RSL cluster.
At least in Queensland there is a set time window from the hospital exposure on March 9. Queensland Health is following up possible links from the hospital end and hopefully they will identify the transmission path(s) so that there is certainty that this cluster is fully identified and contained, and importantly so that it may be prevented from happening again.