# Seroprevalence of SARS-CoV-2 infection in pediatric patients in a tertiary care hospital setting

## TL;DR

This study found that many children had undetected SARS-CoV-2 infections, with higher rates during the Delta-Omicron period and links to household exposure and symptoms.

## Contribution

The study provides new insights into pediatric SARS-CoV-2 seroprevalence and identifies risk factors and immunological markers in a hospital setting.

## Key findings

- Seroprevalence in children rose significantly during the Delta-Omicron period compared to the pre-Delta period.
- Household exposure and respiratory symptoms were key risk factors for SARS-CoV-2 seropositivity in children.
- Nucleocapsid IgG levels were associated with pneumonia in pediatric patients with COVID-19.

## Abstract

Globally, cases of children’s coronavirus disease 2019 (COVID-19) have been reported since the pandemic started. Most children have an asymptomatic or mild infection. Therefore, the incidence rate of COVID-19 in children might have been underestimated. This study aimed to determine (1) the seroprevalence (and seroconversion rates) of COVID-19, including associated risk factors, in pediatric patients visiting hospitals; and (2) the immunological responses to COVID-19. This was a prospective, cross-sectional study. Patients aged 0–18 years who visited the hospital from September 2020 to February 2022 were included. Demographic, clinical, and laboratory data were reviewed. A total of 1,443 pediatric patients were enrolled. Of these, 323 (22.6%) had a history of COVID-19. In the pre-Delta period, the seroprevalence increased from 4.1% to 70.6% in all included patients and from 0.5% to 10% in patients without a known history of COVID-19 compared with the Delta-Omicron period. The seroconversion rate was 6.8% (19 per 100 person-years) in pediatric patients with COVID-19. Risk factors for COVID-19 seropositivity were respiratory symptoms, being in an outpatient department setting, and infection during the Delta-Omicron period. Exposure to household members with confirmed COVID-19 was a risk factor for seropositivity and seroconversion. Infection during the Delta-Omicron period and testing conducted >2 weeks after the onset of symptoms was associated with spike immunoglobulin (Ig) M and spike and nucleocapsid IgG, respectively. High nucleocapsid IgG levels were associated with pneumonia in pediatric patients with COVID-19. Pediatric patients exposed to household members with COVID-19 and respiratory symptoms should be tested for COVID-19. Nucleocapsid IgG can be used as a surrogate marker to identify patients who may have experienced pneumonia from COVID-19 and as a screening tool for the COVID-19 outbreak, regardless of COVID-19 vaccination status.