A longitudinal study of healthcare workers' surveillance during the ongoing COVID-19 Epidemics in Italy: is SARS-CoV-2 still a threat for the Health-care System? (preprint)

Objectives: In spring 2020, Northern Italy was the first area outside China to be involved in the SARS-CoV-2 pandemic. This observational study depicts SARS-CoV-2 prevalence and serological curves among first-line healthcare workers (HCWs) at Padua University Hospital (PdUH), North-East Italy. Method: 344 HCWs, working at the PdUH Emergency Department and Infectious Disease Unit, underwent a SARS-CoV-2 RNA nasopharyngeal swab with paired IgM and IgG antibody detection for 4 consecutive weeks. At every session, a questionnaire recorded symptoms, signs and recent contacts with SARS-CoV-2 patients. Positive cases were followed up for 5 months. Results: Twenty-seven HCWs (7.84%) had positive serology (Abs) with 12 positive swabs during the study period. Two additional HCWs were positive by swab but without Abs. Fourteen cases (4%) had SARS-CoV-2 infection before the beginning of the study. An HCW with autoimmune disease showed false Ab results. 46% of individuals with Abs reported no symptoms, in accordance with previous population studies. Fever, nasal congestion, diarrhoea and contacts with SARS-CoV-2 individuals correlated to SARS-CoV-2 infection. 96% of Abs+ cases showed persistent positive antibodies 5 months later and none was re-infected. Discussion: Correct use of PPEs and separate paths for positive/negative patients in the hospital can result in a low percentage of SARS-CoV-2 infections among HCWs, even in high risk settings. Frequent testing for SARS-CoV-2 with nasopharyngeal swabs is worthwhile, irrespective of HCWs' symptoms, due to the lack of specificity together with the high percentage of asymptomatic cases. Further studies are needed to elucidate the neutralizing effect of SARS-CoV-2 antibodies.

Salivary SARS-CoV-2 antigen rapid detection: a prospective cohort study (preprint)

Background SARS-CoV-2 quick testing and reporting are now considered relevant for the containment of new pandemic waves. Antigen testing in self-collected saliva might be useful. We compared the diagnostic performance of salivary and naso-pharyngeal swab (NPS) SARS-CoV-2 antigen detection by a rapid chemiluminescent assay (CLEIA) and two different point-of-care (POC) immunochromatographic assays, with that of molecular testing. Methods 234 patients were prospectively enrolled. Paired self-collected saliva (Salivette) and NPS were obtained to perform rRT-PCR, chemiluminescent (Lumipulse G) and POC (NPS: Fujirebio and Abbott; saliva: Fujirebio) for SARS-CoV-2 antigen detection. Results The overall agreement between NPS and saliva rRT-PCR was 78.7%, reaching 91.7% at the first week from symptoms onset. SARS-CoV-2 CLEIA antigen was highly accurate in distinguishing between positive and negative NPS (ROC-AUC=0.939, 95%CI:0.903-0.977), with 81.6% sensitivity and 93.8% specificity. This assay on saliva had an overall good accuracy (ROC-AUC=0.805, 95%CI:0.740-0.870), reaching the optimal value within 7 days from symptom onset (Sensitivity: 72%; Specificity: 97%). POC antigen in saliva had a very limited sensitivity (13%), performing better in NPS (Sensitivity: 48% and 66%; Specificity: 100% and 99% for Espline and Abbott respectively), depending on viral loads. Conclusions Self-collected saliva is a valid alternative to NPS for SARS-CoV-2 detection not only by molecular, but also by CLEIA antigen testing, for which the highest diagnostic accuracy was achieved in the first week from symptom onset. Saliva is not suitable for POC, although the accuracy of these tests appears satisfactory for NPS with high viral load.

Frequent testing regimen based on salivary samples for an effective COVID-19 containment strategy (preprint)

Rapid and accurate diagnostic tests are essential for controlling the ongoing COVID-19 pandemic. Although the current gold standard involves testing of nasopharyngeal swabs specimens by nucleic acid amplification test, such as real-time reverse-transcription polymerase chain reaction (rRT-PCR) to detect the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it presents several limitations that ultimately may translate into a bottleneck in the surveillance regimen. New strategies based on frequent testing using less invasive specimens are urgently needed for containment of the infection. Rapid antigen assay using saliva as a reliable alternative to nasopharyngeal swabs should be proposed as a valuable part of the overall testing strategy.