Background:We aimed to identify risk factors causing critical disease in hospitalized children with COVID-19 and to build a predictive model to anticipate the probability of need for critical care. Methods: We conducted a multicenter, prospective study of children with SARS-CoV-2 infection in 52 Spanish hospitals. The primary outcome was the need for critical care. We used a multivariable Bayesian model to estimate the probability of needing critical care. Results:The study enrolled 350 children from March 12, 2020, to July 1, 2020: 292 (83.4%) and 214 (73.7%) were considered to have relevant COVID-19, of whom 24.2% required critical care. Four major clinical syndromes of decreasing severity were identified: multi-inflammatory syndrome (MIS-C) (17.3%), bronchopulmonary (51.4%), gastrointestinal (11.6%), and mild syndrome (19.6%). Main risk factors were high C-reactive protein and creatinine concentration, lymphopenia, low platelets, anemia, tachycardia, age, neutrophilia, leukocytosis, and low oxygen saturation. These risk factors increased the risk of critical disease depending on the syndrome: the more severe the syndrome, the more risk the factors conferred. Based on our findings, we developed an online risk prediction tool (https://rserver.h12o.es/pediatria/EPICOAPP/, username: user, password: 0000). Conclusions: Risk factors for severe COVID-19 include inflammation, cytopenia, age, comorbidities, and organ dysfunction. The more severe the syndrome, the more the risk factor increases the risk of critical illness. Risk of severe disease can be predicted with a Bayesian model.

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Objectives To determine the time to RT-PCR negativity after the first positive RT-PCR test, factors associated with longer time to RT-PCR negativity, proportion of children seroconverting after proven SARS-CoV-2 infection, and factors associated with the lack of seroconversion. Study design EPICO-AEP is a multicenter study conducted in Spanish children to assess the characteristics of COVID-19. In a subset of patients, three serial RT-PCR tests on nasopharyngeal swab specimens were performed after the first RT-PCR test, and IgG serology for SARS-CoV-2 antibodies was performed in the acute and follow up (<14 and ≥14 days after diagnosis) phase. Results In total, 324 patients were included in the study. Median [IQR] time to RT-PCR negativity was 17 [8–29] days, and 35% of patients remained positive >4 weeks after the first RT-PCR test. The probability of RT-PCR negativity did not differ across groups defined by sex, disease severity, immunosuppressive drugs, or clinical phenotype. Globally, 24% of children failed to seroconvert after infection. Seroconversion was associated with hospitalization, persistence of RT-PCR positivity and days of fever. Conclusions Time to RT-PCR negativity was long, regardless of severity of symptoms or other patients’ features. This should be considered when interpreting RT-PCR results in a child with symptoms, especially those with mild symptoms. Seroprevalence and post-immunization studies should consider that one in four infected children fail to seroconvert.

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