key: cord-0775136-l0yqxi29
authors: Barbaro, F.; Della Rocca, F.; Padoan, A.; Aita, A.; Vito, C.; Basso, D.; Cattelan, A.; Donato, D.; Plebani, M.; Dall'Olmo, L.
title: 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?
date: 2021-02-24
journal: nan
DOI: 10.1101/2021.02.23.21249481
sha: 902fb94ea2cdd6fa16942b19eab2ef091be4a7a2
doc_id: 775136
cord_uid: l0yqxi29

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.

The new Coronavirus disease 2019 (COVID-19) pandemic represents the most serious global challenge after the Second World War, with many publichealth and economic consequences. The SARS-CoV-2 epidemic spread out in December 2019 in the Wuhan Province of Hubei, China, and Italy was the first country outside Asia to be involved. The municipality of Vo' Euganeo, 30 Km from PdUH, was recognized as the first COVID-19 cluster in Europe after the first confirmed death, the 27 th of February 2020. More than 200 Italian physicians have died of COVID-19 up to the end of November 2020. While waiting for an available and efficient vaccine against the virus, prevention of interpersonal diffusion remains the most effective measure to limit viral spread.

SARS-CoV-2 transmission among HCWs remains a significant concern to date, not only for the risk of HCWs of becoming infected but also infecting patients, co-workers and family members. It should also be taken into careful consideration that transmission might occur from symptomatic, but mainly from asymptomatic subjects. SARS-CoV-2 diagnosis should be confirmed by positive molecular results of nasopharyngeal swabs, while serology remains a relevant laboratory test to identify previous or silent infections.

During the COVID-19 outbreak in spring 2020, this longitudinal study followed up HCWs of 3 first-line wards of PdUH,in order to estimate: 1) the incidence of SARS-CoV-2 infections and/or illnesses among HCWs by rRT-PCR from nasopharyngeal swabs; 2) the time-course of SARS-CoV-2 IgM and IgG serological determinations.

This prospective study was carried out between April 8 and May 29, 2020 (week 15-22 of 2020) at PdUH, a tertiary-care hospital in the Veneto Region (Northeast Italy). In February 2020, PdUH developed an emergency plan for the COVID-19 outbreak that included a COVID-19 triage prior to entry to the hospital and dedicated areas for COVID-19 suspected and confirmed cases (1) . HCWs were provided with personal protective equipment (PPE) according with eCDC and National Health 2 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The IDU ward was dedicated to the admission of confirmed COVID-19 patients, while the IDU AT was a temporary outpatient clinic for the first evaluation of mildly symptomatic patients and the execution of nasopharyngeal swabs in tents. (1) .

A total of 344 HCWs underwent SARS-CoV-2 RNA nasopharyngeal swabs with paired IgM and IgG antibody detection, once a week for 4 consecutive weeks. At every session, a questionnaire was administered to participants, recording the demographic characteristics, the professional role, the presence of comorbidities and clinical symptoms and signs (e.g., fever, cough, nasal congestion, sore throat, diarrhoea, dyspnea) and eventual contacts with SARS-CoV-2 patients in the last week. Only positive participants for SARS-CoV-2 serology were followed up for 5 months and tested at the end of this period with both nasopharyngeal swabs and serology. All participants were informed about the purpose and procedures of the study and gave informed consent. The study was conducted in accordance with the Declaration of Helsinki. Participation was voluntary; subjects could withdraw at any time and all analyses were carried out on anonymized data. HCWs were evaluated for body temperature and symptoms at the beginning of every shift.

-Nasopharyngeal swabs: nasopharyngeal swabs were performed by using flocked swabs in a liquidbased collection and transport system (eSwab®, Copan Italia Spa, Brescia, Italy). All nasopharyngeal swab samples were processed with an in-house Real-Time Polymerase Chain Reaction (RT-PCR) method according to Lavezzo et al. (4) . All tests were performed at the Clinical 3 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in Microbiology and Virology Unit of PdUH, which is the regional reference laboratory for emerging 

Statistical analyses were performed using Stata v16.1 (Statacorp, LakeWay drive, TX, USA). Mean and standard deviation or median and interquartile range and percentages were used as descriptive statistics for normally distributed, or skewed distributed variables, as appropriate. Fisher's exact test was employed to evaluate differences across groups in categorical variables. To assess differences among groups, T-test and ANOVA were performed with continuous data. Exact logistic regression was employed to define the association between studied variables and SARS-CoV-2 positive testing. The user community command 'xtgraph' was used to plot time kinetics of IgM and IgG antibodies in the study period, while spaghetti plots were plotted using Stata native command 'xtline'. and professional qualifications as covariates, age was associated with professional qualification (F = 10.83, p < 0.001), clinicians being younger than nurses or healthcare assistants. 

This prospective study reports the results of an epidemiological investigation on first-line HCWs who participated with keen interest at PdUH, Italy, during the first wave of the SARS-CoV-2 outbreak in spring 2020. Participants were followed up and tested 4 times for both SARS-CoV-2 using nasopharyngeal swabs and serology every week. Additionally, positive cases were tested again after 5 months. A questionnaire about COVID-19 symptoms and contacts with confirmed cases was administered at every test point.

We found a low incidence of SARS-CoV-2 positivity to nasopharyngeal swabs and serology, 4.07% and 7.85% respectively, in agreement with some reports by other authors as well as a regional serosurvey (6) . The low prevalence of SARS-CoV-2 infection in our context could be related to the strict observance of preventive measures against viral transmission among HCWs adopted in our 5 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in Class 2: 14 HCWs were positive to SARS-CoV-2 antibodies only, with repeated negativity to swabs. In 1 HCW, the positivity to SARS-CoV-2 antibodies only was related to a significant comorbidity (multiple sclerosis) and therefore has been interpreted as an analytic interference and 6 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for this this version posted February 24, 2021. ; https://doi.org/10.1101/2021.02.23.21249481 doi: medRxiv preprint excluded from the study analysis. The remaining 13 cases of this class had an asymptomatic or paucisymptomatic infection, before time zero of our study. Class 3: 12 HCWs were positive to both SARS-CoV-2 nasopharyngeal swab and anti SARS-Cov-2 antibodies, and therefore must be considered SARS-CoV-2 acute phase infections during the study period.

The remaining 315 HCWs, negative to both swab and antibodies, can be considered SARS-Cov-2 free throughout the entire study period.

We found no correlation between gender, professional qualification and place of work with SARS-CoV-2 infection in HCWs, in agreement with other studies (14, 16) . The logistic regression analysis showed no significant differences for study variables (place of work, professional qualification, development and type of symptoms, previous contact with confirmed COVID-19 patients, relevant comorbidities and past seasonal flu vaccination) in Abs+ cases, regardless of positive or negative swab. None of Abs+ cases developed a new infection and 89% (24/27) of them had persistent IgG after 5 months. This is in accordance with similar reports (17) and was confirmed by three different Ab tests, whose neutralizing activity is currently under evaluation in our lab (data not shown). As for adaptive immunity, the hypothesis of IgG being a protective immune response to a pathogen goes back more than a century and nevertheless remains even now a fundamental biological principle to establish (18) .

The concept behind this and similar studies is not only a safety issue. It also deals with potential benefits and current costs. Testing asymptomatic and symptomatic HCWs is worthwhile to avoid workforce depletion in settings (i.e., Emergency and Infectious Disease Units) that are already at full stretch. It has been reported that in the USA more than 125,000 HCWs were unnecessarily selfisolating due to the lack of specificity of SARS-CoV-2 symptoms. On the other hand, the high number of asymptomatic cases rendersasymptomatic personnel a significantly underestimated potential source of contagion. In 3 independent studies dealing with extensive testing of closed populations (i.e., Vo' Euganeo, the Diamond Princess cruise ship and the Icelandic population), the number of asymptomatic SARS-CoV-2 positive individuals exceeded 40%, and more than 70% of cases positive to swabs had no symptoms or mild disease (4, 19, 20) .

Consistently, other studies reported asymptomatic SARS-CoV-2 infections varying between 1.7% and 4.2%, of all tested HCWs, independently of infection source (i.e., acquired inside the hospital or in the household setting) and accounting for nearly half of all of the positive HCWs (13, 15, 16, 21) . Despite all of the fears during the first wave of the SARS-CoV-2 epidemic, evidence is showing an overall reduced risk of COVID-19 for HCWs, highlighting the chance of retrieving effective surveillance protocols from daily experience (1, 15, 16) . 7 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for this this version posted February 24, 2021. ; https://doi.org/10.1101/2021.02.23.21249481 doi: medRxiv preprint A significantly increased risk, up to 3-6 times, of COVID-19 for HCWs compared with the general population was initially reported because of contacts with COVID-19 patients, inadequate use of PPE, management of infective patients and underestimation of viral diffusion on the part of the staff (22, 23) . The risk of HCW SARS-CoV-2 infection was significantly increased for staff on duty in non-COVID-19 wards due to inexperience and lack of training (22) . In our IDU AT, between February 21th and April 16th 2020, 12,822 SARS-CoV-2 nasopharyngeal swabs were performed on variably symptomatic patients with a daily average of 228 swabs and a rate of swab positivity of 4.3% (544/12.822 pts). 60 HCWs were on duty in this daily service and were regularly tested with anaverage of 6 swabs each (range 4.3-7.1, total number of swabs performed on HCWs 361). No cases of COVID-19 were detected among HCWs during all ofthe IDU AT activity (1).

In conclusion, this study depicts the effect of a strategy to prevent viral spread among HCWs. The measures adopted by our Institution for first-line settings were those of pandemics with a high risk of HCW contagion (i.e., comparable to Ebola threat, for whom an educational effort was adopted in 2014) and are part of the "Test, Trace and Isolate" strategy, followed by the Veneto Region where the swabs are available to all contacts of positive cases.

The correct use of PPE, avoiding their re-use, management of confirmed or suspected COVID-19 patients in dedicated areas of the hospital, the virological and serological surveillance of HCWs and the training of staff contributed to the effective control of interpersonal viral spreading.

Furthermore, refresh sessions regarding preventive and isolation procedures were planned to avoid staff risk underestimation related to persistent exposure to the virus.

During the first wave of the SARS-CoV-2 spread in spring 2020, we found a low incidence of infected HCWs and could therefore hypothesize the absence of transmission among first-line HCWs. Positive HCWs seemed to have been infected outside the hospital, mainly by relatives, as reported by the personal interviews of cases.

Transmission and prevention of infections among HCWs remain issues of global interest, the ongoing spread of SARS-CoV-2 being a current Public Health Emergency of international concern (22-26).

A possible limitation of this study is that it was carried out during the national lock-down of spring 2020 with a limited sample size and single centre design; consequently, our results should be interpreted with caution.

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We sincerely thank our head nurses, for their endless support and coordination effort: Dott.ssa Suzanne Judet, PS AOUP; Dott.ssa Ilaria Guarnieri, PS OSA; Dott.ssa Lorella Diserò and Dott.ssa Donatella Rampado, IDU AT and Ward.

All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint inThe copyright holder for this this version posted February 24, 2021. ; https://doi.org/10.1101/2021.02.23.21249481 doi: medRxiv preprint