key: cord-0878553-0kf4i1a4 authors: Soriano-Arandes, Antoni; Soler-Palacin, Pere; Borras-Bermejo, Blanca; Antón, Andrés title: Prevalence of asymptomatic SARS-CoV-2 infection in children undergoing hospital screening date: 2020-10-13 journal: Enferm Infecc Microbiol Clin DOI: 10.1016/j.eimc.2020.10.004 sha: 614b116edf77382615ece1f285241e166e01eb31 doc_id: 878553 cord_uid: 0kf4i1a4 nan described in all age groups with children representing only about 2-5% of all cases worldwide (1) (2) (3) (4) . Such low percentages could be explained by a higher number of asymptomatic coronavirus disease 2019 in children, along with milder symptoms (5) , so they are less likely to be studied. Moreover, data from countries that have performed universal screening at the community level suggest that children have low overall prevalence, as showed in an Icelandic study where children under 10 years of age tested all negative for the SARS-CoV-2 real-time polymerase chain reaction (RT-PCR) (6) . Otherwise, we yet know that children might be much less important spreaders for SARS-CoV-2 transmission than adults (7) (8) (9) . However, these studies were performed before or during lock-down measures were implemented, and their results should be taken with caution. Detailed epidemiological studies including childhood data will be very useful to guide public health decisions regarding school reopening. We report on cases of asymptomatic SARS-CoV-2 infection among children screened before admission at a reference children's hospital in Barcelona (Catalonia, Spain) . We screened asymptomatic adults and children for SARS-CoV-2 by RT-PCR in respiratory samples who had to be admitted for any cause or subjected to a procedure over the airway, from May 4th to June 11th, 2020, once lock-down measures were partially released and children were allowed to go out with their relatives (figure 1). Those cases previously confirmed of SARS-CoV-2 were excluded from testing. Patients, or parents or legal tutors of children were asked for symptoms or recent contact with a person with suspected or confirmed COVID-19 disease within the last 14 days. time RT-PCR assays (Allplex™ 2019-nCoV, Seegene, Korea, or Cobas® SARS-CoV-2, Roche Diagnostics, USA) at our Microbiology laboratory. We recorded the demographic features, exposure history, and RT-PCR results. During the study-period, 3,777 RT-PCR tests were performed for universal screening. Among those, 3,380 were adults and 397 were children. Infection prevalence rates of SARS-CoV-2 infection were 0.27% (9/3,380) among adults, and 1.0% (4/397) among children, significantly higher than adult rate (p=0.017). Among the 397 asymptomatic children the median [IQR] age was 9 [4-13] years, 58% (230/397) were male. No significant differences were observed for testing positive SARS-CoV-2 by sex (p=0.74) or by age (p=0.18). The four asymptomatic case-patients had an epidemiological link (household contact) with a confirmed adult COVID-19 case. These findings suggest a very low (1%) prevalence of positive SARS-CoV-2 test results among asymptomatic children under 18 years of age during the post-peak period of the epidemic in Spain, when children have been allowed to enjoy their playing time in the street but not to attend school. As strength, this study shows the prevalence of SARS-CoV-2 infection during a low-incidence period among this population, when restriction of testing was not a dairy challenge due to the limited availability of tests, and hence, no selection bias occurred by focusing laboratory confirmation mainly on those cases with clear symptomatology. In contrast, asymptomatic children were more likely to have a positive result for SARS-CoV-2 RT-PCR than adults (p=0.017) reinforcing the fact that children have at least the same probability to be infected than adults, as suggested by other authors (1-4) . SARS-CoV-2 transmission (10) . Aligned with this, in our data we found that all the positive children had an adult as an epidemiological link. Our report has some limitations, firstly the sample size of asymptomatic positive cases is relatively small, and secondly the study is limited to a single healthcare center. In conclusion, despite the low prevalence found in the universal screening, it allowed us to implement preventive and control measures for the new diagnosed cases. These results should be interpreted with caution, as data was collected right after the end of confinement measures, and the epidemiology situation changes over time. However, as children are returning to the new "normality", screening of asymptomatic SARS-CoV-2-infected cases among this population seems reasonable to monitor COVID-19 prevalence in children. Vall d'Hebron Hospital Universitari, Vall d'Hebron Barcelona Hospital Campus, Passeig Vall Vall d'Hebron Institut de Recerca (VHIR), Vall d'Hebron Hospital Universitari, Vall d'Hebron Barcelona Hospital Campus, Passeig Vall d'Hebron 119-129 08193 Bellaterra Vall d'Hebron Hospital Universitari, Vall d'Hebron Barcelona Hospital Campus, Passeig Vall d'Hebron 119-129 Hebron Hospital Universitari, Vall d'Hebron Barcelona Hospital Campus, Passeig Vall d'Hebron 119-129 Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China Chinese Center for Disease Control and Prevention Coronavirus Disease 2019 (COVID-19) in Italy Screening and Severity of Coronavirus Disease 2019 (COVID-19) in Children in 2019-nCoV CDC Response Team. Initial Public Health Response and Interim Clinical Guidance for the 2019 Novel Coronavirus Outbreak -United States Epidemiology of COVID-19 Among Children in China Spread of SARS-CoV-2 in the Icelandic Population Cluster of coronavirus disease 2019 (Covid-19) in the French Alps Children and the Dynamics of Infection in Families No evidence of secondary transmission of COVID-19 from children attending school in Ireland Agedependent effects in the transmission and control of COVID-19 epidemics Details of the postconfinement measures adopted by the Spanish government are depicted below the curve Acknowledgments: We thank the nursing team involved in the sample collection. We thank the nursing team involved in the sample collection.