Symptomatic Infants Have Higher Nasopharyngeal SARS-CoV-2 Viral Loads but Less Severe Disease Than Older Children

To the Editor—Published data suggest lower rates of severe coronavirus disease 2019 (COVID-19) in pediatric age groups [1, 2]. However, the relative contribution of infants and children to community transmission is not known. Data from China suggest that children were infected early in the outbreak [3]. A report published in this journal described the presence of a high nasopharyngeal (NP) viral load of severe acute respiratory coronavirus 2 (SARS-CoV-2) in a well infant [4]. Whether this observation is generalizable to symptomatic infants, and how it compares to NP viral loads in older children and adolescents, is not known. Studies in adults have demonstrated a positive correlation between viral load and COVID-19 severity [5]. While some data have suggested a higher disease severity in infants [2, 6], how NP viral load correlates with severity across the pediatric age spectrum has not been firmly established. Here we report NP viral load among infants, children, and adolescents who were hospitalized and discharged from our children’s hospital from 14 March to 24 April 2020. All patients were tested either in the emergency department or during inpatient hospitalization based on symptoms suggestive of COVID-19. For each patient, we extracted age, time from reported symptom onset to the date of test, and severity of disease during hospitalization. Severity of COVID-19 disease was determined by (1) the need for respiratory support with noninvasive positive-pressure ventilation and/or mechanical ventilation or (2) intensive care unit (ICU) admission. All testing was performed by reverse transcriptase–polymerase chain reaction with the Cobas SARS-CoV-2 assay (Roche Molecular Systems, Inc, Branchburg, NJ). Cycle threshold (Ct) values, which are inversely proportional to viral RNA concentration, were used to measure relative viral loads. Target 2, a conserved region of the structural protein envelope E-gene, was used for these purposes as it was the most consistently amplified target. We used Student’s t tests to compare mean Ct values between age groups and Fisher’s exact tests to compare categorical variables. Among 57 patients testing positive for SARS-CoV-2, 20 (35.1%) were infants 12 months of age or younger. Older children and adolescents ranged from 1 year to 21 years of age. Mean NP viral load was significantly higher in infants as compared with older children and adolescents (mean Ct, 21.05 vs 27.25; P < .01) (Figure 1). However, a significantly lower proportion of infants had severe disease as compared with the older patients (n = 1 [5%] vs n = 12 [32.4%]; P = .02). Mean time to test positivity from symptom onset was lower in infants than older children (2 vs 3.8 days, P < .01). Similar proportions in both groups were tested within 7 days of symptom onset (91.2% vs 100%, P = .47). Nasopharyngeal swab viral loads and severity of disease compared across infants compared with older children. Abbreviation: Ct, cycle threshold. Our report suggests that symptomatic infants have higher NP viral loads at presentation but develop less severe disease as compared with older children and adolescents. Whether this is attributable to slightly earlier presentation to clinical care versus host biology requires investigation. These data have implications for mitigating spread, especially in congregate settings (eg, child care centers) or hospital units (eg, neonatal ICUs) that serve this group. Potential conflicts of interest. The authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest.

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