Infectivity of severe acute respiratory syndrome coronavirus 2 in children compared with adults

Abstract

Background: The role of children in the transmission and community spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unclear. We aimed to quantify the infectivity of SARS-CoV-2 in nasopharyngeal samples from children compared with adults.

Methods: We obtained nasopharyngeal swabs from adult and pediatric cases of coronavirus disease 2019 (COVID-19) and from their contacts who tested positive for SARS-CoV-2 in Manitoba between March and December 2020. We compared viral growth in cell culture, cycle threshold values from the reverse transcription polymerase chain reaction (RT-PCR) of the SARS-CoV-2 envelope (E) gene and the 50% tissue culture infective dose (TCID₅₀/mL) between adults and children.

Results: Among 305 samples positive for SARS-CoV-2 by RT-PCR, 97 samples were from children aged 10 years or younger, 78 were from children aged 11-17 years and 130 were from adults (≥ 18 yr). Viral growth in culture was present in 31% of samples, including 18 (19%) samples from children 10 years or younger, 18 (23%) from children aged 11-17 years and 57 (44%) from adults (children v. adults, odds ratio 0.45, 95% confidence interval [CI] 0.28-0.72). The cycle threshold was 25.1 (95% CI 17.7-31.3) in children 10 years or younger, 22.2 (95% CI 18.3-29.0) in children aged 11-17 years and 18.7 (95% CI 17.9-30.4) in adults (p < 0.001). The median TCID₅₀/mL was significantly lower in children aged 11-17 years (316, interquartile range [IQR] 178-2125) than adults (5620, IQR 1171 to 17 800, p < 0.001). Cycle threshold was an accurate predictor of positive culture in both children and adults (area under the receiver-operator curve, 0.87, 95% CI 0.81-0.93 v. 0.89, 95% CI 0.83-0.96, p = 0.6).

Interpretation: Compared with adults, children with nasopharyngeal swabs that tested positive for SARS-CoV-2 were less likely to grow virus in culture, and had higher cycle thresholds and lower viral concentrations, suggesting that children are not the main drivers of SARS-CoV-2 transmission.

Figure 1:

Reverse transcription polymerase chain reaction cycle threshold values of the severe acute respiratory syndrome coronavirus 2 envelope gene by age group. Adult samples had a significantly lower cycle threshold value (18.7, interquartile range [IQR] 17.9–30.4) than children aged ≤ 10 years (25.1, IQR 17.7–31.3, p < 0.001) and those aged 11–17 years (22.2, IQR 18.3–29.0, p = 0.02).

Figure 2:

Tissue culture infective dose 50% (TCID₅₀/mL) by age group. Adult samples had significantly higher TCID₅₀/mL (5620, IQR 1171–17 800) than children aged 11–17 years (316, interquartile range [IQR] 178–2125, p < 0.001), but were not significantly higher than children aged ≤ 10 years (1171, IQR 316 to 5620, p = 0.1).

Figure 3:

Symptom onset to test time (days), the mean revere transcription polymerase chain reaction cycle threshold value of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) envelope gene and the probability of successful viral culture in pediatric samples. The probability of SARS-CoV-2 culture is shown by the pink bars. Black lines represent 95% confidence intervals. Cycle threshold values are represented by the blue line, with circles representing medians and blue bars representing the 95% confidence intervals. Numbers above the pink bar indicate the number of samples per day.