Keeping up with COVID: identification of New Zealand's earliest known cluster of COVID-19 cases.

Becker, Elizabeth; Vipond, Richard; Mansell, Chris

We report the earliest known cluster of SARS-CoV-2 infection so far reported, which occurred in New Zealand in late February 2020. The cluster includes one confirmed and five probable cases. The cluster was identified while investigating a weak positive nasopharyngeal swab (NPS) polymerase chain reaction (PCR) test that was returned by a male in his 60s in September 2020. The PCR result, combined with a clear clinical and epidemiological history of a COVID-19 like illness in late February 2020, prompted serological testing. SARS-CoV-2 IgG antibodies were detected and supported historical infection. Serology was also reactive for five close contacts who had also experienced a COVID-19 like illness in February 2020. Combined case histories and investigations suggest that this local cluster was import related, with the index case identified as a family member visiting from Italy in February. Case investigation also suggests this cluster was active in New Zealand prior to any previously documented local cases, indicating that SARS-CoV-2 was present and local transmission was occurring earlier than initially suspected. A weak positive PCR result, six months after acute infection, supports international evidence that SARS-CoV-2 genetic material can be detected for several months after initial COVID-19 infection, and that this is not necessarily indicative of infectivity.