Children With Croup and SARS-CoV-2 Infection During the Large Outbreak of Omicron.

To the Editor:

In children, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) commonly presents with fever, cough or shortness of breath or is sometimes asymptomatic.[1] There have been few case reports about croup caused by SARS-CoV-2 infection, which is a rare symptom, and its characteristics or clinical presentations have not been sufficiently revealed.[2,3] In the current pandemic involving SARS-CoV-2 variants, especially Omicron VOC21NOV-01 (B.1.1.529), we report three cases of Japanese patients with Omicron-induced croup within a short period.

A 3-month-old boy presented to the emergency department with a 1-day history of fever and dyspnea. He was febrile and appeared agitated with tachypnea, inspiratory stridor, and a hoarse cry, as well as severe subcostal retraction and nasal flaring. A nasopharyngeal polymerase chain reaction test was positive for SARS-CoV-2. He was diagnosed with COVID-19 and severe croup. Nebulized epinephrine and oral dexamethasone were administered, but his condition showed little improvement. He was thus admitted and treated with nebulized epinephrine every 3 hours and intravenous dexamethasone. His symptoms gradually improved, and he was discharged on day 4.

We also experienced an 8-month-old boy and a 21-month-old boy who did not respond well to treatments for croup at the emergency department, similar to the previous case. The 8-month-old boy had persistent symptoms lasting 3 days, which eventually improved.

We suggest that the risk of croup is higher with Omicron than it is with other variants. This is supported by recent findings that the possibility of sore throat is higher in patients with Omicron infection than in those with Delta infection, indicating that Omicron may cause severe inflammation in the upper respiratory tract.[4] In vitro research has reported that Omicron infects individuals and quickly replicates in the upper respiratory tract and bronchus, whereas other variants mainly replicate in the alveolar epithelium.[5] These findings are consistent with our suggestion that Omicron infection can induce croup.

From the viewpoint of infection control, we must consider SARS-CoV-2 infection when examining a patient with croup. SARS-CoV-2 can be transmitted via aerosols, and nebulizer use is believed to increase the transmission risk. We have to perform SARS-CoV-2 testing in patients with croup and use airborne precautions for them when nebulized epinephrine is administered during the outbreak of Omicron.

Our cases indicate that patients with Omicron-induced croup may have poor responses to nebulized epinephrine and glucocorticoids and may show symptom improvement after a long time. This is consistent with past cases involving croup caused by other variants.[2,3] Our cases suggest that the number of hospitalizations involving Omicron-induced croup is increasing in the current outbreak, although Omicron is associated with reduced severity and a lower rate of hospitalization compared with other variants.

In conclusion, the risk of croup appears to be higher with Omicron than with other variants, and it might result in a life-threatening condition. The number of patients with Omicron-induced croup will continue to increase as this variant spreads worldwide. It is important to recognize the epidemiology and characteristics of patients with Omicron-induced croup.