Sensitivity of serology assay in Covid-19 diagnosis: does the antigen matter?

Since the spreading of Sar-CoV-2 in March 2020, many serologic tests have been developed to identify antibody responses. Indeed, different commercial kits are directed against different antigens and could utilise different methods thereby triggering confusion and criticism. Here, we compared two Food and Drug Administration (FDA)-approved automatized assays that detect IgG responses against spike or nucleocapsid protein of Sars-Cov-2 virus in 127 subjects among healthcare workers of IRCCS Policlinico San Donato (MI), Italy. We observed different kinetics of IgG responses, demonstrating the importance of timing of sampling to correctly interpret the results both for infection diagnosis and for epidemiologic studies. We observed that Anti-N response starts earlier than Anti-S1/S2 response but also decreases earlier, affecting the sensitivity of the tests at different time points. Combining two different assays, designed against different antigens, could reduce false negative results. Finally, we observed a patient who produced anti-nucleocapsid IgG, but not anti-spike IgG. In conclusion, we investigated antibody responses in Covid-19 disease, aiming to direct clinicians and laboratory scientists to correctly interpret serologic results by always paying attention to clinical history correlation, timing of sampling, methods and antigens used, to avoid false negative results and obtain relevant epidemiologic data.

Prevalence of multidrug-resistant organisms in migrant children admitted to an Italian cardiac surgery department, 2015-2016.

Screening on hospital admission to identify multidrug-resistant organism (MDRO) colonization is a frequently discussed topic. We report the results of microbiological screening in 141 Italian and 354 migrant children candidates for cardiac surgery conducted in 2015-2016. In all, 25% of Italian children and more than 65.4% of African and Romanian children carried at least one MDRO (meticillin-resistant Staphylococcus aureus; extended-spectrum ß-lactamase enzymes; carbapenemase producers; and vancomycin-resistant enterococci). Based on our findings, we propose that non-geographically limited approaches are needed to improve infection prevention and control.