Development and validation of a nanoplate-based digital PCR assay for absolute MPXV quantification

Quantification of mpox virus (MPXV) across different human body anatomical sites can provide insights about the most likely transmission routes, so methods able to release absolute and exact quantitative values of MPXV DNA are crucial. Here, we optimized a new QIAcuity digital PCR (dPCR) protocol for the detection and quantification of MPXV DNA in clinical samples and assessed the performance of the assay by comparing the results obtained in 144 biological samples with those resulting from the use of an in-house real-time PCR (qPCR). Overall, the concordance between the two assays was 95%, with samples identified concordantly as MPXV DNA positive and having a mean number of copies per μl of 1708 (95% CI: 107-2830 copies/μl). The remaining samples gave discordant results, with 5 out of 7 detected with the QIAcuity dPCR assay but not with the in-house qPCR. MPXV DNA levels measured by QIAcuity dPCR were strongly correlated with the Ct values detected by in-house qPCR and with those detected by another dPCR assay previously developed in our laboratories. The QIAcuity dPCR assay may be a robust and easy-to-perform method for MPXV DNA quantification in several biological samples.