Results
Tests were performed from 6th to 19th May 2020, after a decline in the number of daily cases in Australia. The peak reporting of cases occurred on the 27th of March 2020 with 460 confirmed cases nationally and 111 cases in Victoria (Figure 1). Overall, 351 women consented SARS-CoV-2 testing. Of those, 332 (94.6%) were tested in antenatal clinic for routine screening and 19 (5.4%) were tested in the maternity ward, birth suite, pregnancy assessment unit, or the COVID-19 screening clinic due to possible symptoms of COVID-19. One patient (0.3%) in the routine screening group could not tolerate the test, and therefore 350 patients underwent testing.
The baseline characteristics of the screened population are summarised in Table 1. The median maternal age of the study population was 32 years (IQR 28 to 35 years). The median gestational age at testing was 33 weeks and four days (IQR 28 weeks to 36 weeks and two days), 148 women (42.2%) were nulliparous and 203 (57.8%) were parous. Ten women (2.9%) were in the first trimester (less than 14 weeks of gestational age), 77 (21.9%) were in the second trimester (from 14 to 28 weeks of gestational age), and 264 (75.2%) were in the third trimester of pregnancy (gestational age of 28 weeks or more).
In the routine screening group, two women (0.6%) reported possible COVID-19 symptoms in the days that preceded the test (one reported headache and one reported rhinorrhea). In the symptomatic group, the most common symptoms were fever (13, 68.4%), respiratory changes including cough and dyspnoea (5, 26.3%) and sore throat (4, 21%). No patients reported recent overseas travel or contact with known infected persons.
All 350 tests were negative for SARS-CoV-2, including those performed in women with symptoms. Using the statistical “rule of three” for approximation of the exact estimation for a binomial distribution with no events occurrence11, 12, we estimate with 95% confidence that the true proportion of positive tests in the population is between 0 and 0.86% (p̂ = 0%, 95% CI 0% to 0.86%).