key: cord-0972887-sbuxk3yl authors: Reichert, Friedrich; Enninger, Axel; Plecko, Thomas; Zoller, Wolfram G.; Paul, Gregor title: Pooled SARS-CoV-2 antigen tests in asymptomatic children and their caregivers: Screening for SARS-CoV-2 in a pediatric emergency department date: 2021-07-24 journal: Am J Infect Control DOI: 10.1016/j.ajic.2021.07.009 sha: e3d4079979e56f38c6f3dc9ee0244220a559fa28 doc_id: 972887 cord_uid: sbuxk3yl BACKGROUND: : Universal admission screening for SARS-CoV-2 in children and their caregivers (CG) is critical to prevent hospital outbreaks. We evaluated pooled SARS-CoV-2 antigen tests (AG) to identify infectious individuals while waiting for PCR test results. METHODS: : This single-center study was performed from November 5, 2020 to March 1, 2021. Nasal mid-turbinate and oropharyngeal swabbing for AG and PCR testing was performed in children with two individual swabs that were simultaneously inserted. Nasopharyngeal swabs were obtained from their CG. AG swabs were pooled in a single extraction buffer tube and PCR swabs in a single viral medium. Results from an adult population were used for comparison, as no pooled testing was performed. FINDINGS: : During the study period, 710 asymptomatic children and their CG were admitted. Pooled AG sensitivity and specificity was 75% and 99.4% respectively for detection of infectious individuals. Four false negatives were observed, though three out of four false negative child-CG pairs were not considered infectious at admission. Unpooled AG testing in an adult population showed a comparable sensitivity and specificity of 50% and 99.7%. AG performed significantly better in samples with lower Ct values in the corresponding PCR (32.3 vs 21, p-value <0.001). CONCLUSIONS: : Pooled SARS-CoV-2 AGs are an effective method to identify potentially contagious individuals prior admission, without adding additional strain to the child. Preventing coronavirus disease 2019 (COVID-19) outbreaks in hospital settings is critical. The paucity of specific symptoms or signs of COVID-19 in children makes sole symptombased screening challenging. Since transmission can occur even in pre-or asymptomatic individuals, universal admission screening for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in all patients is mandatory in Germany (1, 2) . A symptom-based COVID-19 testing strategy failed to identify nearly half of all hospitalized children infected by SARS-CoV-2 in a French multicenter cohort (3) . In a pediatric emergency department, isolation pending the polymerase chain reaction (PCR) result (up to 24 hours) is only feasible for a limited number of patients. So, only symptomatic patients are isolated due to having a higher pre-test-probability of infection. Rapid lateral-flow SARS-CoV-2 antigen tests (AG) are fast, simple, and cheap, but less sensitive than PCR tests which are considered the gold standard (4) . PCR tests on the other hand are usually performed in centralized labs and therefore the method drives down frequency and speed of testing. Combining the best of both worlds would consequently be the optimal screening strategy prior to the admission of asymptomatic children and their caregivers (CG). Performing multiple tests on children (e.g., antigen testing followed by PCR testing) can be traumatic. Moreover, parallel testing in children and their CG drives up costs, as two AG and two PCR tests would be needed for every admission to the children's hospital. To reduce the number of traumatic practices in children and to save resources, we implemented a procedure of pooled AG and PCR testing in asymptomatic children and their CG prior admission. Simultaneous swabbing for AG and PCR tests allows testing without additional strain to the child and the pooled approach reduces costs. The goal of this study was to evaluate this test strategy as a universal screening method in a pediatric emergency department. The study period started right at peak of the second wave in [removed for double blind review] with a seven-day incidence rate of 182 per 100,000 on November 5, 2020. By the end of the study period the valley between the second and third wave was reached, with a seven-day incidence rate of 50 per 100,000 on March 1, 2021. The SARS-CoV-2 Rapid Antigen Test by SD Biosensor (SD BioSensor Inc., Suwon, South In children, AG and RT-PCR testing was performed simultaneously with two individual swabs. Both swabs were first inserted into the mouth and the back wall of the oropharynx was swabbed. The same swabs were then used to perform a mid-turbinate nasal swab. The original swab from the antigen test is then put into the extraction buffer tube. The swab for the RT-PCR was collected in Copan Universal Transport Medium (Copan, Murietta, USA). For testing of the accompanying CG, the swabs were not carried out simultaneously. For antigen testing, a nasopharyngeal swab was performed, according to manufacturer instructions. The swab was put in the same extraction buffer tube as the swab from the child. For RT-PCR testing, an oropharyngeal as well as nasopharyngeal swab was performed. The swab was pooled in the same virus transport medium as the swab from the child. In case of a positive pooled RT-PCR result, individual swabbing of the child and their CG was performed as soon as the result of the pooled test was available. The same sampling technique was applied in the adult emergency department, as was done for the adult CG in the pediatric emergency department, though no pooling of swabs was performed. The study was approved by the local ethics committee (vote 119/2021BO2), with waiver of informed consent due to the retrospective and anonymized approach. Continuous data were expressed as mean and standard deviation (SD), while categorical variables are reported as number (n), percentage (%) and 95% confidence interval (CI). Statistical differences between Ct values of negative or positive antigen tests were determined using Student's t-test. Reported p-values are 2-tailed, with P ≤ 0.05 being considered statistically significant. SPSS (SPSS 24, SPSS Inc., Armonk NY, USA) was used for statistical analysis. During the study period, 710 asymptomatic children and their CG were admitted and tested via the pediatric emergency department. Detection rates in asymptomatic individuals of pooled AG and PCR were 0.99% (7/703) each. Four false positive as well as four false negatives were observed with AG ( Table 1) . AG sensitivity, specificity, positive and negative predictive value were as follows: 42.9% (95% CI 9.9-81.6%), 99.4% (98. 6 (Figure 1 ). All samples with Ct values below 21 were correctly identified by AG. During the ongoing COVID-19 pandemic, screening every child and their CG for active infection with SARS-CoV-2 prior hospital admission is critical to prevent nosocomial infections. A systematic review showed that around 15% of children and new-borns have asymptomatic infection (5) . Therefore, screening asymptomatic children is essential for infection control in a children's hospital. SARS-CoV-2 RT-PCR from nasopharyngeal swabs is considered the gold standard, but test results are often delayed for several hours or days. To isolate every child while waiting for the PCR test results, even without upper respiratory tract symptoms, would lead to overflow in pediatric emergency departments. Lateral flow SARS-CoV-2 antigen tests (AG) are cheap, easy to use and have a rapid turnaround time and hence allow for rapid identification of infectious individuals. In our study we show that AGs detect most asymptomatic children and their CG with COVID-19 that are considered infectious at the time of admission. This was possible despite pooling AG swabs from children and their CG, which saves resources and money. Nasopharyngeal swabs are an uncomfortable and often traumatic experience for children. Especially the nasal passage is irritating. Studies in adults have shown that nasal midturbinate or even anterior nasal sampling for AGs are reliable alternatives to nasopharyngeal swabbing (6,7). We therefore collected nasal mid-turbinate as well as oropharyngeal swabs from children, instead of nasopharyngeal swabs. In our experience, this approach leads to a higher acceptance rate in children, which is especially important in chronically ill children, which are admitted to the hospital on a regular basis. To further reduce the trauma of sampling for the children, we used two swabs simultaneously in one passage. One swab was used for the AG, while the other was used for the PCR analysis. Due to a child's anatomy, this is only possible by using thin swab such as provided with the SD Biosensor AG. Several studies have shown that AGs show reduced sensitivity in asymptomatic individuals, when compared to symptomatic individuals (8) (9) (10) (11) . This is also true in children (12) . We show that pooled antigen testing has a sensitivity of 43%, which is well within the expected range according to literature. As this was a retrospective, non-interventional study, we did not have a control group, where AG testing was performed without pooling. Studies have shown that viral loads in nasopharyngeal samples are comparable between children and adults (13) . Though, recent studies have shown that viral loads might be slightly lower in very young children, but is probably not of clinical relevance (14) . Therefore, we compared the results to asymptomatic adults visiting the adult emergency department, where AG testing was performed according to manufacturer instructions via unpooled nasopharyngeal swabbing. Sensitivity of the AG in asymptomatic adults was 38.9%, which is comparable to the results from the pediatric emergency department population. Although both cohorts are not directly comparable, we cautiously conclude that pooling of AG test swabs led to no dramatic decrease in diagnostic sensitivity. We would not recommend using pooled AG tests as a sole screening test for asymptomatic individuals, especially in a low disease prevalence setting. The performance of a test not only depends on test related sensitivity and specificity, but also on local endemicity of the disease. Especially if an individual with a positive AG test has a low likelihood of disease (e.g., asymptomatic or fully vaccinated individuals, low prevalence setting), a confirmatory nucleic acid amplification test should follow (15) . Though, they add an additional layer of protection by identifying most infectious but asymptomatic child and CG pairs at the time of hospital admission. Thus, they contribute significantly to COVID-19 control measures. False negative results are not uncommon with AG, but many such samples had PCR Ct values above 30, indicating low viral RNA counts, which falls in line with published literature (16-18) . Consequently, many such individuals were identified after the infectious period has passed. The cut-off of Ct value < 30 as a marker for contagiousness was arbitrarily applied. The biggest benefit of AG in a pediatric emergency department lies in the rapid identification of highly contagious individuals while waiting for the PCR test results. Ct values are not directly comparable between assays, but the Robert Koch Institute, Germany's national Public Health Institute, used a Ct value cut-off of 30 as a guidance in the past (19). Other studies saw no viral growth already in samples with a Ct value above 24, whilst others not till Ct values above 33 (20, 21) . Our study has several limitations. Only a small number of patients had SARS-CoV-2 infection, limiting the robustness of data. We are not able to answer the question whether pooling the AG test between the child and their CG reduced sensitivity. Because of the observational design, no control group was available. Comparison to an adult population without pooled antigen tests was used as a proxy, but the different sampling technique (midturbine + oropharyngeal vs nasopharyngeal) and the different populations (children vs adults) allowed no direct comparison. Recent studies show that viral loads in children tend to be slightly lower compared to adults (14) . This is partly explained by smaller swab sizes, but further complicates the comparison of both groups. Our study shows that pooled antigen tests for SARS-CoV-2 of asymptomatic children and their CG inserts an additional layer of protection prior admission in a pediatric emergency department, while waiting for PCR test results. Simultaneous nasal mid-turbinate swabbing for the antigen and PCR test adds no additional strain to the child and pooling swabs from the child and their CG in a single AG keeps additional costs low. The authors declare no conflict of interest. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Tables Table 1: SARS-CoV-2 -Testkriterien für die SARS-CoV-2 Diagnostik bei symptomatischen Patienten mit Verdacht auf COVID-19 SARS-CoV-2 Transmission From People Without COVID-19 Symptoms Systematic SARS-CoV-2 screening at hospital admission in children:a French prospective multicenter study Rethinking Covid-19 Test Sensitivity -A Strategy for Containment SARS-COV-2 infection in children and newborns: a systematic review Anterior nasal versus nasal mid-turbinate sampling for a SARS-CoV-2 antigen-detecting rapid test: does localisation or professional collection matter? medRxiv Head-to-head comparison of SARS-CoV-2 antigen-detecting rapid test with professional-collected nasal versus nasopharyngeal swab Antigen-Based Test for Asymptomatic and Symptomatic SARS-CoV-2 Testing at Two University Campuses -Wisconsin Urgent need of rapid tests for SARS CoV-2 antigen detection: Evaluation of the SD-Biosensor antigen test for SARS-CoV-2 COVID-19) Antigen Card test relative to the severe acute respiratory coronavirus virus 2 (SARS-CoV-2) real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay among symptomatic and asymptomatic healthcare employees Point-of-care evaluation of a rapid antigen test (CLINITESTⓇ Rapid COVID-19 Antigen Test) for diagnosis of SARS-CoV-2 infection in symptomatic and asymptomatic individuals Performance and Implementation Evaluation of the Abbott BinaxNOW Rapid Antigen Test in a High-throughput Drive-through Community Testing Site in Massachusetts CoV-2 viral loads in young children do not differ significantly from those in older children and adults Estimating infectiousness throughout SARS-CoV-2 infection course Interim Guidance for Antigen Testing for SARS-CoV-2 Field evaluation of a rapid antigen test (Panbio TM COVID-19 Ag Rapid Test Device) for COVID-19 diagnosis in primary healthcare centres Clinical Evaluation of Self-Collected Saliva by Quantitative Reverse Transcription-PCR Reverse Transcription-Loop-Mediated Isothermal Amplification, and a Rapid Antigen Test To Diagnose COVID-19 Evaluation of a SARS-CoV-2 rapid antigen test: Potential to help reduce community spread Predicting infectious SARS-CoV-2 from diagnostic samples Viral RNA load as determined by cell culture as a management tool for discharge of SARS-CoV-2 patients from infectious disease wards None.