  Background: Worldwide demand for SARS-CoV-2 RT-PCR testing is increasing as
more countries are impacted by COVID-19 and as testing remains central to
contain the spread of the disease, both in countries where the disease is
emerging and in countries that are past the first wave but exposed to
re-emergence. Group testing has been proposed as a solution to expand testing
capabilities but sensitivity concerns have limited its impact on the management
of the pandemic. Digital PCR (RT-dPCR) has been shown to be more sensitive than
RT-PCR and could help in this context.
  Methods: We implemented RT-dPCR based COVID-19 group testing on commercially
available system and assay (Naica System from Stilla Technologies) and
investigated the sensitivity of the method in real life conditions of a
university hospital in Paris, France, in May 2020. We tested the protocol in a
direct comparison with reference RT-PCR testing on 448 samples split into
groups of 3 sizes for RT-dPCR analysis: 56 groups of 8 samples, 28 groups of 16
samples and 14 groups of 32 samples.
  Results: Individual RT-PCR testing identified 25 positive samples. Using
groups of 8, testing by RT-dPCR identified 23 groups as positive, corresponding
to 26 true positive samples including 2 samples not initially detected by
individual RT-PCR but confirmed positive by further RT-PCR and RT-dPCR
investigation. For groups of 16, 15 groups tested positive, corresponding to 25
true positive samples identified. 100% concordance is found for groups of 32
but with limited data points.
