Detection and quantification of SARS-CoV-2 by droplet digital PCR in real-time PCR negative nasopharyngeal swabs from suspected COVID-19 patients. - Alteri C; Cento V; Antonello M; Colagrossi L; Merli M; Ughi N; Renica S; Matarazzo E; Di Ruscio F; Tartaglione L; Colombo J; Grimaldi C; et al. (PloS one, 2020)