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.