key: cord-0717941-fmiu3xxb
authors: Kasztelewicz, B.; Janiszewska, K.; Burzynska, J.; Szydłowska, E.; Migdał, M.; Dzierzanowska-Fangrat, K.
title: Prevalence of IgG antibodies against SARS-CoV-2 among healthcare workers in a tertiary pediatric hospital in Poland
date: 2020-11-30
journal: nan
DOI: 10.1101/2020.11.28.20239848
sha: 16f9bf6228f69b41e4305c0eb033a95f320cbb1a
doc_id: 717941
cord_uid: fmiu3xxb

Data on prevalence of SARS-CoV-2 antibody in healthcare workers (HCWs) is scare, especially in pediatric settings. The purpose of this study was to evaluate the SARS-CoV-2 IgG-positivity among HCWs of a tertiary pediatric hospital. In addition, follow-up of serological response in the subgroup of seropositive HCWs was performed, to get some insight on persistence of IgG antibodies to SARS-CoV-2. Free, voluntary SARS-CoV-2 IgG testing was made available to HCWs of the Children's Memorial Health Institute in Warsaw (Poland). Plasma samples were collected between July 1 and August 9, 2020 and tested using the Abbott SARS-CoV-2 IgG assay. Of 2282 eligible participants, 1879 (82.3%) HCWs volunteered to undergo testing. Sixteen HCWs tested positive for SARS-CoV-2 IgG, corresponding to the seroprevalence of 0.85%. Among seropositive HCWs, three had confirmed COVID-19. Of note, 8 (50%) seropositive HCWs reported neither symptoms nor unprotected contact with confirmed SARS-CoV-2 cases in the previous months. A decline in the IgG index was observed at median time of 86.5 days (range:84-128 days) after symptom onset or RT-PCR testing. The nationwide public health response measures together with infection prevention and control practices implemented at the hospital level, at the beginning of the COVID-19 pandemic, might explain a low seroprevalence. Further studies are warranted to elucidate the duration of anti-SARS-CoV-2 antibodies, as well as the correlation between seropositivity and protective immunity against reinfection. Regardless of the persistence of antibodies and their protective properties, such low prevalence indicates that this population is vulnerable to a second wave of the COVID-19 pandemic.

CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint Introduction 35 Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease 2019 (COVID-36 19) which emerged in December 2019, has evolved to a global pandemic [1] . In Poland first, imported COVID-37 19 case was reported on March, 3 2020 and 3 weeks later a nationwide lockdown was commenced [2] . Until 38 August, 31, there were 66 870 confirmed cases, with 2 033 COVID-19 related deaths [3] .

In the Masovian district (one of the three most affected regions in Poland) the first cases were recorded on 40 March 13 and by the end of August 2020, there were 9370 cases and 411 deaths [4] .

Although real-time RT-PCR is considered the gold standard for the diagnosis of the acute SARS-CoV-2 42 infection, this test is limited by transient nature of RNA. In addition, the sensitivity of RT-PCR methods is 43 estimated to be no higher than 70% [5] , which may lead to underdiagnosing of SARS-CoV-2 infections, 44 especially in subclinical or asymptomatic cases. By identifying individuals who have developed antibodies to the 45 virus (including those that may be asymptomatic or have recovered), serology can give greater details into the 46 prevalence of SARS-CoV-2. Although, concerns have arisen on persistence of IgG antibodies to SARS-CoV-2 47 after recovery [6, 7] .

Two entitles of infected individuals pose the highest risk for SARS-CoV-2 transmission in the hospital setting.

First, infected patients until diagnosis. Second, SARS-CoV-2-positive health care workers (HCWs). As children 50 and adolescent comprise less than 5% of all positive cases in Europe [8] , majority of SARS-CoV-2 infections 51 among HCWs in pediatric hospitals might be associated with transmission in community or from infected co-52 workers.

Data on SARS-CoV-2 prevalence among HCWs in pediatric hospital settings is scare [9, 10] 

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The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint 4 pharmacists, administrative staff, maintenance, etc.). All participants were asymptomatic at the time of serology 64 testing. In particular, those who were previously symptomatic, had no symptoms for at least 14 days. Plasma 65 (EDTA) samples were collected between July 1 and August 9, 2020 (corresponding to 97 -135 days after the 66 nation-wide lockdown was commenced).

Plasma samples were run on the Abbott Alinity i instrument using the Abbott SARS-CoV-2 IgG assay (Abbott 68 Laboratories, Lake Bluff, IL, USA) following manufacturer's instruction. The assay is a chemiluminescent 69 microparticle immunoassay (CMIA) for qualitative detection of IgG antibodies to the nucleocapsid (N) protein 70 of SARS-CoV-2. The manufacturer's index value (a signal/cut-off; S/CO ratio) of ≥ 

Since that time until August 9, 2020 (i.e. the end of the serology testing), additional 4 linked cases among 89 laboratory staff, were confirmed by RT-PCR (Fig 1) . 

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The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint 5 first case of SARS-CoV-2 RNA among HCWs of CMHI was detected on March, 17 2020. Voluntary serological 94 testing for HCWs of CMHI was conducted from July 1 to August 9, 2020 (corresponding to week 27 and 32). is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint 6 administration of RT-PCR test does not imply that a HCW was suspected of having COVID-19, since tests were 122 also performed as a part of contact tracing, in previously quarantined or isolated HCWs before return to work or 123 in newly employed staff). The median time between RT-PCR and serology testing was 77 days (IQR: 39-122 124 days). SARS-CoV-2 RNA was detected in 4 of 417 HCWs, including 3 HCWs with positive serology (details 125 given below). The remaining one, with a positive SARS-CoV-2 RNA test, was seronegative. This was the HCW 126 whose plasma was collected 129 days post RT-PCR testing.

127 Fifty-six HCWs had been quarantined or isolated. The median time since the start of quarantine or isolation to 128 serology testing was 97.5 days (IQR: 42.5-126 days) ( 

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The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint 

.

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The odds of being seropositive were higher in HCWs who had been previously tested by RT-PCR regardless of 159 the test results (adjusted OR=3.82, 95% CI: 1.42-10.29; p=0.008) ( Table 3) . The age, sex, professional category 160 or working in clinical area, did not show any statistically significant association with the positivity for SARS-161 CoV-2 IgG ( Table 3) .

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The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint Table 3 . Analysis of factors associated with SARS-CoV-2 IgG positivity. In addition, we monitored three initially seronegative HCWs, diagnosed with COVID-19 within a week following their first serology testing (i.e. in the week 27). All three were epidemiologically linked and thus considered clustered cases with intra-hospital transmission. These HCWs were immediately put on home isolation as soon as they were identified by RT-PCR testing (all experienced mild symptoms). After their return to work, SARS-CoV-2 IgG was tested twice in convalescent plasma samples collected 34-37 and 84-85 days after the RT-PCR testing. Decrease in the index value were observed in all 3 cases between the second and the third month after symptom onset.

Overall, all six HCWs remained seropositive while tested on the last sample collected at the median time of 86.5 days (range: 84-128 days) after symptom onset or RT-PCR testing (Fig 2) . 

In Poland, a nationwide lockdown, including closure of school, public institutions, and mandatory face-mask was implemented during the very early stages of the COVID-19 pandemic [2] . As a result, the daily numbers of new SARS-CoV-2 infections have been relatively stable up to the study period with cumulative incidence of . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint Seroprevalence studies in HCWs allow for assessing the level of exposure, and indirectly, the effectiveness of implemented protective measures. They are also crucial to inform health care resource planning to provide safe environment to protect both patients and HCWs from SARS-CoV-2 infection. A few seroprevalence studies of HCWs in pediatric hospitals have been published so far. Here, we present the results of serology testing in HCWs of the large pediatric hospital in Poland, including over 82% of employees. In our study SARS-CoV-2

IgG positivity rate was 0.85%, and it was lower than in previous reports from pediatric hospitals. The seroprevalence of SARS-CoV-2 among 175 HCWs in a large referral pediatric hospital in Barcelona was 4% [10] . Another study form Italy, performed at the same time (i.e. mid-April 2020), showed seroprevalence of 5.13% [12] . Timing of serology testing (April 2020 vs July 2020) and significantly higher burden of COVID-19 (as Spain and Italy were two most affected countries in Europe, [13] ) may account for this difference. In addition, and in contrast to Spanish and Italian reports, we did not have any confirmed COVID-19 case among patients in our hospital until the end of the study period.

Interestingly, we did not observe any difference in seroprevalence between clinical and non-clinical working locations or across professional groups. This may be due to the fact that at that time we did not managed any children with confirmed COVID-19. Although asymptomatic SARS-CoV-2 carriage among hospitalized children cannot be completely ruled out (since RT-PCR screening on admission is not 100% sensitive to preclude infection), the risk of children to staff transmission seems to be low. The recent study from pediatric hospital in Chicago, revealed a low (1-2 %) prevalence of SARS-CoV-2 among children without COVID-19 symptoms as well as no secondary transmission among HCWs exposed to these patients [14] . Another study, comparing dynamics and determinants of SARS-CoV-2 transmissions among HCWs of adult and pediatric settings in Paris, revealed significantly lower attack rate in the pediatric setting (2.3% vs 3.2%, respectively) [15] .

In our study, prior RT-PCR testing regardless of the result, was associated with increased adjusted risk of SARS-CoV-2 IgG positivity. This may be a reflection of the fact that, testing for SARS-CoV-2 RNA was performed as a part of contact tracing and in previously quarantined or isolated HCWs before return to work. Considering that as many as 50% of seropositive HCWs in our study were asymptomatic or had no confirmed contact with suspected or proven COVID-19 case, and that over 80% (13/16) had not been tested or tested negative for SARS-CoV-2 RNA, it could indicate that some SARS-CoV-2 infections among HCWs were unrecognized or undetected. Although, false-positive SARS-CoV-2 IgG results are possible (e.g. due to cross-reactivity to commonly circulating human coronaviruses) they are unlikely, even in the limited circulation of the virus [11] .

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13 Thus, it seems reasonable to test both symptomatic and asymptomatic HCWs for SARS-CoV-2 RNA on a regular basis, if resources are available.

We evaluated antibody persistence in a subgroup of HCWs with multiple plasma samples available for serology testing, to get some insight into antibody persistence. SARS-CoV-2 IgG antibodies were detected up to 128 days post symptoms onset or RT-PCR testing. However, the index value declined consistently in all subjects between first and last plasma sample tested. Our findings are in line with some previously published data on kinetics of SARS-CoV-2 IgG [16, 17] . Recent study by Strömer et al. evaluated SARS-CoV-2 IgG levels in follow-up samples from 16 individuals (median time of the last sample submission was 153 days after the RT-PCR) and revealed that several SARS-CoV-2 infected patients lost their N-specific IgG within a few months or could lose them soon [16] . Of note, in contrast to N-specific IgG, the response to the spike (S) protein was found to be more stable and was associated with the presence of virus-neutralizing antibodies (although at relatively low titres).

Another study by Patel et al., evaluated change in antibodies to SARS-CoV-2 over 60 days among 19 HCWs (including symptomatic ones), using S-based assay [17] . They observed a decrease in anti-SARS-CoV-2 antibodies in all HCWs, with 58% of seropositive individuals becoming seronegative. Taking together, these findings suggest that seroprevalence studies may underestimate rates of prior infections as antibodies may only be transiently detectable after infection. Nevertheless, the limited number of HCWs with follow-up sample available precludes any meaningful conclusion. In contrast to ours and two studies mentioned above, a recent population-based study, implementing two highly sensitive and specific assays to monitor antibody levels and their durability, indicated that antibody remained stable over 4 months. These discordant results may be attributed to sampling biases [18] . Thus, larger longitudinal serological studies are warranted, including these with virus neutralization assays, to explore the dynamic and the persistence of the SARS-CoV-2 antibodies as well as their correlation with immunoprotection from reinfection.

Our study has some limitations which should be acknowledged. First, testing spanned an over a 5-week period (week 27 -32), potentially leading to changes in incidence over time and possible variation in professional groups attending testing. Second, we cannot rule out that some of HCWs were infected and either mounted no detectable antibody response or it had weaned by the time of serology testing, as we had found one of confirmed COVID-19 case seronegative 129 days after the positive RT-PCR test. Thus, the seroprevalence in our study could be underestimated. Moreover, data on symptoms, exposure histories or personal protective equipment use were collected only for the subset of seropositive HCWs by telephone interview (subjected to recall bias), therefore more detailed information on risk factors could not be assessed. Nevertheless, so far this is the largest . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint study assessing the prevalence of SARS-CoV-2 IgG antibodies among HCWs in the pediatric hospital setting, with a high response rate and the use of high-quality serological assay. Our study provides data on the seroprevalence of SARS-CoV-2 infection among HCWs in the pediatric setting in the initial peak of the pandemic, which inform control and prevention strategies for future waves of COVID-19 pandemic.

SARS-CoV-2 seroprevalence in healthcare workers of a tertiary pediatric hospital in Poland is low (0.85%). The nationwide public health response measures together with infection prevention and control practices implemented at the hospital level, at a start of COVID-19 pandemic, might explain a low seroprevalence. Further studies are warranted to elucidate the duration of anti-SARS-CoV-2 antibodies, as well as the correlation between seropositivity and protective immunity against reinfection. Regardless of the persistence of antibodies and they protective properties, such low prevalence indicates that this population is vulnerable to a second wave of COVID-19 pandemic.

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. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprintThe copyright holder for this this version posted November 30, 2020. ; https://doi.org/10.1101/2020.11.28.20239848 doi: medRxiv preprint