A New Point-of-care Test Based on Differential Leucocyte Count, Suitable for a Mass Screening Program to Detect SARS-CoV-2: A Diagnostic Accuracy Study

Introduction. In June 3rd, 2020, the Italian government started the so-called "Phase 2", which included the re-opening of working and social activities. In this framework, the issue of how to identify the asymptomatic individuals who, unwittingly, can spread SARS-CoV-2 infection and pose a threat to public health has been raised worldwide. The mondial population are now experiencing the phase 3 of the pandemic with a rapid increase in the spreading of infection and in the occurrence of new cases. It is now imperative to guarantee the health and safety of the people called back to work and to create a safety protocol in commercial and meeting spaces, which means preventing infected people from causing new epidemic outbreaks. For this purpose, a well-established mass screening program is required to meet several needs: first, it should provide the result in a few minutes, it should be easily delivered on the territory, non-medical healthcare professionals should perform it in a simple way also, and should be non-invasive, repeatable and reliable.

To date, the diagnosis of SARS-CoV-2 infection is made by identifying the viral RNA in samples collected through a nasopharyngeal swab or other respiratory samples. This technique, however, has several limitations for its application in a mass screening, among which the most important ones are the time necessary for the diagnosis, the crowding of those centers appointed to analyze the specimens, and the non-negligible risk of viral transmission to the healthcare workers.

Point-of-care testing with rapid turnaround times would allow more effective triage in settings where patient management and infection control decisions need to be made rapidly.

Recently, it has been developed a new method of acquitting the occurrence of severe Sar-COV-2 infection and resulting COVID-19, detecting the early rise in leukocyte levels which has a characteristic set of ratios of leukocyte types, which identify the viral pathogen and distinguish it from a number of others. This test allows prediction of positives from full blood count results, sensitive up to 14 days earlier than real-time quantitative PCR (RT-qPCR), at a cost at least an order of magnitude lower than other tests such as RT-qPCR and antibody tests.

Aim of the study. Primary aim of the Diagnostic Accuracy study is to validate the use of the point-of-care characteristic Differential Leucocyte Count (CLDC) device and algorithm to detect SARS-CoV-2 infection in both symptomatic and asymptomatic individuals as a preliminary approach to a mass screening program. The comparison is represented by the nasopharyngeal swab molecular testing, the gold standard of COVID-19 diagnosis, for algorithm validation and hematological cytometric analyses by Coulter HMX, Beckman Coulter, for device validation.