By the middle of December 2020, COVID-19 cases in NSW were almost completely restricted to overseas travellers in hotel quarantine. NSW was looking forward to further easing of public health restrictions ahead of the end-of-year festive season. However, on 16 December the Northern Sydney Public Health Unit was notified of two confirmed COVID-19 cases among Avalon Beach residents. The cases knew each other, but the source of their infections was unknown. There was a rapid escalation in cases reported from the area, with approximately 20 cases notified each day for the next four days.
Rapid upstream investigations revealed that two social events held at two local community clubs in the middle of December were the source of the outbreak. While no index case could be identified, these two superspreading events were responsible for a growing number of cases then linked to smaller clusters elsewhere in the Northern Beaches Local Government Area (NBLGA). The risk of spread to other areas in Sydney and beyond was clear.
Key outbreak control measures included intensive case and contact tracing conducted by the Northern Sydney Public Health Unit with the assistance of public health units from other NSW local health districts, and investigations of venues linked to cases. NBLGA residents were advised to restrict their movements as much as practical and get a COVID-19 test if they developed symptoms. This resulted in a phenomenal community response with an estimated 40% of residents tested by day 5 of the outbreak. With the rapid escalation in cases, a stay-at-home public health order was issued on 19 December. Given the geographical location, this order was able to be restricted to NBLGA residents.
A total of 151 confirmed cases were epidemiologically linked to this outbreak. Whole genome sequencing of samples linked a further 13 cases across NSW to the cluster. Whole genome sequencing also identified the outbreak virus as an Alpha variant which had been reported from the USA at the same time, but no link to travellers from that country could be established.
This outbreak highlighted the capacity for large gatherings at social functions to become COVID-19 superspreading events. However, the very strong public health network response, together with localised community movement restrictions and strong community engagement, led to the successful containment of this explosive outbreak within four weeks of the initial case. This also meant it was not necessary to extend the NBLGA public health order to other areas of Sydney or NSW, with the order being repealed on 9 January 2021.
Adelaide Nyinawingeri1, Sean Tobin1, Katherine Todd1, Michael Staff1
