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Seroprevalence of SARS-CoV-2 among children visiting a hospital during the initial Seattle outbreak

Our take —

In this preprint study, which has not yet been peer-reviewed or published in a journal, residual serum samples were collected from 1076 children at the Seattle Children’s Hospital in March and April, 2020; of these samples, a total of ten tested positive. This resulted in a documented history of infection for April of just over 1%. Of these ten children, two tested positive via RT-PCR and were the only ones with documented symptoms. This study design allowed for an assessment of infection, and hence exposure, to SARS-CoV-2 among both symptomatic and asymptomatic child patients.

Study design


Study population and setting

Children presenting at the Seattle Children’s Hospital for any clinical reason between March 3 and April 24th, 2020, received blood draws. A total of 1775 residual serum samples were collected from 1076 children and serologically screened for IgG antibodies to SARS-CoV-2 by a multi-assay algorithm. Assessment of whether children underwent RT-PCR viral testing for SARS-CoV-2 was also conducted.

Summary of Main Findings

Of the 1775 samples tested, 12 samples from ten different children were identified to be seropositive for SARS-CoV-2 IgG antibodies. One seropositive sample was from late March, and the remainder of seropositive samples were from the second week of April and onward. This resulted in a history of infection of just over 1% for the month of April. Among the ten seropositive children identified, two tested positive via RT-PCR for the virus, three tested negative, and the remaining five never received a test. The two who tested positive via RT-PCR had documented symptoms; none of the other seropositive children had symptoms.

Study Strengths

The approach in this study — unlike others — did not rely on symptom-based viral testing. Instead, this study used serological assays to determine prior exposure to SARS-CoV-2. These serological assays detect antibodies induced by infection rather than detecting the virus itself. This approach likely captured a more representative sample of the overall population, as compared to relying on symptomatic patients to present to the hospital for viral testing. This study also examined whether the antibodies had neutralizing activity.


Though not limited to children exhibiting symptoms for COVID-19, children who presented to the hospital during the study period likely had urgent medical needs that required them to seek care during the stay-at-home order. Therefore, this study likely only represents children with urgent medical needs whose parents sought care on their behalf. Furthermore, the number of children who tested positive was small (n=10), so any analyses on this subgroup should be interpreted with caution.

Value added

This study presents evidence of the history of SARS-CoV-2 infections among children in Seattle for April 2020.

This review was posted on: 4 July 2020