Comorbidity increases severe illness rate from COVID-19 in young children


In a recent study, children aged under 5 years with COVID-19 more often presented with severe illness when comorbid with another respiratory illness.

Pediatric patients aged under 5 years hospitalized with COVID-19 are more likely to experience increased symptom severity when comorbid with other respiratory illnesses, according to an article published by the American Academy of Pediatrics.

There were over 100,000 children hospitalized with COVID-19 from March 2020 to February 2022. The efforts to decrease transmission of COVID-19 during this time was associated with decreased circulation of other respiratory viruses. However, during surges of COVID-19, increases in the incidence of viruses such as respiratory syncytial virus (RSV) was observed.

Investigators hypothesized cases of comorbidity with COVID-19 and respiratory viruses would lead to different clinical characteristics than isolated COVID-19. To evaluate this hypothesis, investigators conducted a cross-sectional study of pediatric patients with COVID-19 from March 1, 2020, to February 28, 2022.

Data was collected from the Coronavirus Disease 2019-Associated Hospitalization Surveillance Network (COVID-NET), spanning 99 counties in 14 states. COVID-NET cases were defined as receiving a positive diagnosis for COVID-19 while residing in a predetermined area during, or within 2 weeks before, hospitalization.

Clinical data gathered included underlying medical conditions history, clinical presentation, COVID-19 vaccination status, diagnostic testing, and clinical course. Children were eligible if they met the definition for COVID-NET surveillance, had completed a case report form, and were hospitalized during the study period for presumed COVID-19 or other respiratory illness.

In the study period, 6487 children were hospitalized with COVID-19 with a complete case report form. Of these, 74% were diagnosed with presumed COVID-19 or other respiratory illness. For those remaining, 62% had at least 1 test for a respiratory virus. Testing for RSV increased during the Delta and Omicron predominant periods.

Children not tested for COVID-19 were more likely to be aged under 5 years, non-Hispanic White, present with upper or lower respiratory symptoms, have a discharge diagnosis connected to respiratory reasons, need intensive care unit admission, have high flow nasal canal, and be given systemic steroids, remdesivir, or intravenous immune globulin.

Comorbidity was found in 21% of children without COVID-19 viral testing. Comorbidity with RSV increased from under 1% before Delta predominance to 13% during Delta predominance and 7% during Omicron predominance.

Upper respiratory symptoms, shortness of breath, and hypoxemia were more common in children with comorbidity. These children also more commonly had a discharge diagnosis of acute respiratory failure, bronchiolitis, asthma exacerbation, or bronchitis.

Children aged under 5 years with comorbidity were at an increased risk of severe respiratory illness, with children aged under 2 years having a significant correlation between RSV comorbidity and severe illness. However, severe illness was not associated with comorbidity among children aged 5 years and older.


Agathis NT, Patel K, Milucky J, et al. Codetections of other respiratory viruses among children hospitalized with COVID-19. Pediatrics. 2023;151(2). doi:10.1542/peds.2022-059037

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Tina Tan, MD, FAAP, FIDSA, FPIDS, editor in chief, Contemporary Pediatrics, professor of pediatrics, Feinberg School of Medicine, Northwestern University, pediatric infectious diseases attending, Ann & Robert H. Lurie Children's Hospital of Chicago
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