Interpretation
The findings of this study are reassuring and likely reflect a stage in the local pandemic context in which community transmission levels were very low, suggesting that widespread routine screening of asymptomatic pregnant women may not be necessary in the context of low community transmission. Under such circumstances, and since pregnant women are no more susceptible to infection than others5, 6, 17, population prevalence estimates can reliably be extrapolated to pregnant women. What remains unknown is whether there is a threshold of community transmission when screening of asymptomatic pregnant women would be warranted given their unique situation of needing to attend hospital repeatedly for antenatal care and for delivery.
Identifying pregnant women who carry the virus is important to allow for treatment of symptomatic individuals, physical isolation of carriers, contact tracing, and implementation of correct PPE­­­­ to reduce transmission risk during antenatal consultations, laboratory testing, ultrasound examinations and during birth that may involve an aerosol generating procedure such as maternal effort in the second stage of labour or endotracheal intubation for general anaesthesia (if required) during caesarean deliveries. Indeed, a similar universal screening study performed in New York City examined 215 pregnant women admitted at the time of labour and found that 15.4% of them had a positive result, of whom nearly 88% (29 of 33 with a positive test) were asymptomatic18. At that time, the number of reported cases in New York ranged from five to over eleven thousand per day1. In a similar smaller study in Japan, 52 obstetric patients admitted to the hospital were tested with PCR, and two (3.8%) had positive results without any symptoms19. The differences observed between the studies can be explained by the diverse regional prevalence of the disease, with much higher asymptomatic community transmission levels in some areas of the United States at the time.
In Australia, mitigation measures such as the closure of the borders and restriction rules were implemented relatively early in the pandemic. The early introduction of these measures likely explains the lower prevalence and fatality rates than most other high-income countries. Indeed, of all tests performed in Victoria since the beginning of the pandemic, only 0.3% were positive10. It is likely that the real positivity (prevalence) rates are even lower because community testing has been focussed on those with symptoms, albeit with a progressively lowering threshold for those symptoms. In the state of Victoria, there are currently 290 diagnosed active cases and an estimated 964 undiagnosed cases due to imperfect detection or absence of symptoms, according to a model available online, at the time this report was written1. Considering a state population of 6.63 million inhabitants20, the prevalence rate of the infection is estimated at 189 infections per one million inhabitants. Notwithstanding, the fear of a possible second wave has been constant, and the interpretation of the epidemiology will need to be revisited as the prevalence and the community transmission rates change with the dynamics of the pandemic.
Universal testing has been proposed not only to reduce transmission rates and avoid an overload of the health systems but also as an alternative strategy to reduce economic and social damage during relaxation of restriction measures, with strict household quarantine after a positive test16. Feasibility, cost and effectiveness of such policy have not, however, been evaluated. In addition, it is unlikely that one single strategy will be enough to assuage the disease burden. Instead, it is the combination of different effective measures that will be able to mitigate the enormous consequences of the pandemic2, 3.