Culture-Competent SARS-CoV-2 in Nasopharynx of Symptomatic Neonates, Children, and Adolescents

Children do not seem to drive transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We isolated culture-competent virus in vitro from 12 (52%) of 23 SARS-CoV-2–infected children; the youngest was 7 days old. Our findings show that symptomatic neonates, children, and teenagers shed infectious SARS-CoV-2, suggesting that transmission from them is plausible.

SARS-CoV-2 vertical transmission without positive nucleic acid testing. The study was also limited by a small sample size. However, these findings show a rapid rate of decline in antibody titers, suggesting lack of protective passive immunity in infants, and IgM detection in infants, supporting a growing body of evidence of possible vertical transmission. We still do not have a correlate of immunity (e.g., we do not know exactly what level of antibody titers are considered protective against infection), and whether infants testing positive by PCR at birth have higher levels of IgM or IgG remains to be seen. More work is needed to understand SARS-CoV-2 immunity in infants; such findings might have implications for potential vaccination efforts.
C hildren are underrepresented in coronavirus disease (COVID-19) case numbers (1,2). Severity in most children is limited, and children do not seem to be major drivers of transmission (3,4). However, severe acute respiratory syndrome Children do not seem to drive transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We isolated culture-competent virus in vitro from 12 (52%) of 23 SARS-CoV-2-infected children; the youngest was 7 days old. Our findings show that symptomatic neonates, children, and teenagers shed infectious SARS-CoV-2, suggesting that transmission from them is plausible. coronavirus 2 (SARS-CoV-2) infects children of all ages (1,3). Despite the high proportion of mild or asymptomatic infections (5), they should be considered as transmitters unless proven otherwise. To address this point, the laboratory of the Geneva University Hospitals and Faculty of Medicine, University of Geneva (Geneva, Switzerland), used cell culture to systematically assess cultivable SARS-CoV-2 in the upper respiratory tract (URT) of 23 children with COVID-19.
All nasopharyngeal specimens (NPS) were collected with a flocked swab in universal transport medium (Floqswab; Copan, https://www.copangroup.com) and tested for SARS-CoV-2 by reverse transcription PCR during January 25-March 31, 2020 (Appendix, https://wwwnc.cdc.gov/EID/ article/26/10/20-2403-App1.pdf). We seeded Vero E6 cells at 8 × 10 4 cells/well in a 24-well plate and inoculated them with 200 μL of viral transport medium the following day. Cells were inoculated for 1 h at 37°C; inoculum was removed; cells were washed once with phosphate buffered saline; and regular cell growth medium containing 10% fetal calf serum was added. We observed cells on days 2, 4, and 6 for cytopathic effect (CPE) by light microscopy. We harvested supernatant at first observation of CPE or, if no CPE occurred, on day 6. For a second passage, we transferred 20 μL supernatant of CPE-positive specimens onto new Vero E6 cells.
We collected supernatant after inoculation and on observation of CPE and confirmed isolation of replication competent SARS-CoV-2 by an increase in viral RNA (Appendix).
We isolated SARS-CoV-2 from 12 (52%) children. We determined SARS-CoV-2 isolation by presence of CPE and increased viral RNA in the supernatant (Table; Appendix Figure). SARS-CoV-2 replication in all 12 positive isolates was confirmed by a second passage.

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Our data show that viral load at diagnosis is comparable to that of adults (6,7) and that symptomatic children of all ages shed infectious virus in early acute illness, a prerequisite for further transmission. Isolation of infectious virus was largely comparable with that of adults, although 2 specimens yielded an isolate at lower viral load (1.2 × 10 4 and 1.4 × 10 5 copies/mL) (6).
A limitation of our study was the small number of children assessed. However, although the Canton of Geneva was a region severely affected by SARS-CoV-2 (8), only 23 cases were diagnosed in children at our hospital during the study period. These findings confirm that children are not a major risk group for COVID-19. Another limitation is our reliance solely on leftover material initially received for routine diagnostic purposes that we retrospectively analyzed. Using such specimens has several disadvantages: preanalytic quality of specimens could be affected by suboptimal times between sample collection and storage at -80°C because of transport and diagnostic processing time, resulting in loss in infectivity and failure of virus isolation even in the presence of high viral load. Therefore, our findings probably underestimate the true rate of infectious virus presence in symptomatic children, and we cannot comment whether our data reflect the rates of infectious virus shedding in the community. Because of the limited leftover volume of the specimens, we were unable to further investigate the quantity of infectious viral particles. Most patients were managed as outpatients and self-isolated at home, so no consecutive sampling was possible to assess infectious virus in multiple samples over the course of disease.
SARS-CoV-2 viral load and shedding patterns of culture-competent virus in 12 symptomatic children resemble those in adults. Therefore, transmission of SARS-CoV-2 from children is plausible. Considering the relatively low frequency of infected children, even in severely affected areas, biological or other unknown factors could lead to the lower transmission in this population. Large serologic investigations and systematic surveillance for acute respiratory diseases and asymptomatic presentations are needed to assess the role of children in this pandemic.

Figure.
Severe acute respiratory syndrome coronavirus 2 initial RNA copy numbers from nasopharyngeal swabs of culturenegative and culture-positive specimens from children <16 years of age, Geneva University Hospitals Geneva, Switzerland, January 25-March 31, 2020. Thick horizontal bars indicate median RNA; thin horizontal bars indicate interquartile range. Asterisk (*) indicates specimen collected outside the institution, suggesting a longer time to freezing at -80°C; dagger ( †) indicates specimen with ≈48 hours from specimen collection to freezing at -80°C.