SARS-CoV-2 Seroprevalence in Children from Western Romania,March to June 2021

Introduction

Epidemiological surveillance of confirmed COVID-19 cases reflects only a part of all infected persons and the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is underestimated (Buonsenso et al. 2021) considering that the real number of asymptomatic infected persons is unknown (Knabl et al. 2021). In this context, assessment of SARS-CoV-2 seroprevalence is important to evaluate the extent of infection in the population. Seroprevalence should be periodically evaluated to anticipate pandemic's dynamic and implement appropriate public health policies (Vaselli et al. 2021). Serologic testing for SARS-CoV-2 antibodies is more reliable in detecting past infection in asymptomatic patients compared to reverse transcription-polymerase chain reaction (RT-PCR) (Byambasuren et al. 2021).

In children, infection with SARS-CoV-2 is generally asymptomatic or exhibits mild symptoms (Lenicek Krleza et al. 2021). To detect previous SARS-CoV-2 infections in asymptomatic individuals, testing for specific antibodies is recommended (Lenicek Krleza et al. 2021, Waterfield et al. 2021).

Limited data are available regarding SARS-CoV-2 sero-prevalence in children. In general, most serologic surveys are based on convenience samples, including children admitted to pediatric hospitals (Lenicek Krleza et al. 2021) undergoing emergency surgery or oncologic care (Sola et al. 2021). Data published in scientific journals by other researchers indicate that SARS-CoV-2 seroprevalence in children varied widely from 0.65% (Lenicek Krleza et al. 2021) in USA to 27.1% in Austria (Knabl et al. 2021).

With more than 1,827,867 SARS-CoV-2 reported cases and more than 58,940 deaths as of January 7, 2022 (European Centre for Disease Prevention and Control, 2022), Romania (19.4 million inhabitants) is among the most affected countries in Europe. In a study conducted between March and June 2021, we found that SARS-CoV-2 seroprevalence was 45.6% in the adult population from Western Romania (Olariu et al. 2022). The sero prevalence of SARS-CoV-2 in the Romanian pediatric population is unknown. Therefore, in this study, we assessed the SARS-CoV-2 seroprevalence in children from Western Romania.

Methods

Serum samples of 379 children were collected between March 10, 2021 and June 10, 2021. To exclude the possibility of maternal antibodies' presence in children's blood, infants younger than 1 year were not included in this study. Children were residents of Timis County (705,113 inhabitants), and were included in the study in the order in which they presented for routine laboratory investigations to Louis Turcanu and Bega Children's Hospital Outpatient Clinics in Timisoara, Romania. There were no specific criteria to select the participants in the study. Samples were analyzed regardless of patients' clinical status and history. Children were grouped into three age categories: 1–5 years (preschool), 6–11 years (elementary school), and 12–17 years (middle/high school).

Serum samples were kept at −20°C until laboratory tests were performed at the Clinical Laboratory of the Municipal Clinical Emergency Teaching Hospital in Timisoara, a reference laboratory for COVID-19 testing in Romania. To identify previous SARS-CoV-2 infections, we used Elecsys Anti-SARS-CoV-2 electrochemiluminiscence immunoassay designed for the Cobas e analyzers (Roche Diagnostics GmbH, Mannheim, Germany) according to manufacturer's protocol.

The assay uses a recombinant nucleocapsid protein (N) for identifying the presence of the serum total antibodies against SARS-CoV-2: IgM, IgA, and IgG. This immunoassay has a specificity of 99.80% and a sensitivity of 99.5% for past infection in patients at ≥14 days after RT-PCR confirmation. Samples with cutoff index ≥1.0 were considered positive.

Results

The 379 children enrolled in the study ranged in age from 1 to 17 years (mean age = 9.06 ± 4.96 years), 263 (69.39%) were residents of urban area, and 190 (50.13%) were females. The overall seroprevalence of SARS-CoV-2 total antibodies was 46.70% (177/379) (Table 1). Statistical data analysis by age groups, area of residence, and gender showed no significant difference between seropositive and seronegative children (Table 1).

Discussion

This study is the first report on seroprevalence of SARS-CoV-2 infection in Romanian children. Our results indicate a 46.70% seroprevalence of SARS-CoV-2 antibodies among children residing in Western Romania, higher than the 8.4% seroprevalence reported in Croatia (Lenicek Krleza et al. 2021), 27.1% in Austria (Knabl et al. 2021), or 35.7% in Italy (Buonsenso et al. 2021).

However, the 39.81% prevalence of SARS-CoV-2 past infection in our preschool children (1–5 years) was lower than the 50% seroprevalence reported in Italy, in the same age group (Buonsenso et al. 2021). Possible explanation for these data would be that studies were conducted in different periods of time, sample size varies from one study to another, diverse sampling strategies with the study group, or sero-logic immunoassays with various sensitivity and specificity (Olariu et al. 2022).

As previously shown, no significant difference in the prevalence of SARS-CoV-2 antibodies was observed according to age or gender (Buonsenso et al. 2021, Waterfield et al. 2021).

This study has limitations. The pediatric collection centers were located only in Timisoara city. This may have contributed to the lower number of study participants from rural areas compared with those from urban areas by limiting the participation of some children from rural areas. Although Louis Turcanu and Bega Children's Hospital Outpatient Clinics in Timisoara are major health institutions where children from all parts of Western Romania are evaluated, our study group may not represent the general pediatric population by age and demographic factors.

In addition, some children previously infected with SARS-CoV-2 during the first or second pandemic waves may have not been detected during this serologic screening, taking into account the waning of antibody response within 4 months (Perreault et al. 2020). Another limitation is that confirmatory virus neutralization tests have not been performed in this study. However, the Elecsys immunoassay detects total antibodies against SARS-CoV-2 and has a high specificity and sensitivity. It is unlikely that the estimated seroprevalence in this study to be significantly influenced by the limitations listed earlier.

In this study, almost half of the investigated children have been previously infected with SARS-CoV-2. The high seroprevalence of SARS-CoV-2 in children (46.70%) indicates the significant spread of the virus during the third COVID-19 pandemic wave. There was no difference between the estimated prevalence in children and the reported prevalence (45.60%) in the adult population from Western Romania during the same period of time, March to June 2021 (Olariu et al. 2022).

Our findings showed a similar seroprevalence of SARS-CoV-2 antibodies in Romanian children and adults, and suggest that children's susceptibility to infection is similar to adults. The seroprevalence reported in this study may be used to guide infection control policy.