Washington, Mar 16 (IANS): While Covid-19 has been generally mild on children, the Omicron wave had a significant effect on them, with an increase in infection and hospitalisation.

Now physicians at Boston Children's Hospital, US, have found manifestation of a previously unrecognised complication of Covid-19 in young children: croup - a type of respiratory illness characterised with barking cough, and noisy breathing.

Known medically as laryngotracheitis, croup is a common respiratory illness in babies and young children. The Mayo Clinic defines croup as an infection of the upper airway, which obstructs breathing and causes a characteristic barking cough and sometimes noisy, high-pitched intakes of breath (known as stridor). In severe cases, it can dangerously constrict breathing.

It usually happens when colds and other viral infections cause inflammation and swelling around the voice box, windpipe, and bronchial tubes.

But in the report, published in a pre-publication in Pediatrics journal, the physicians noted that just over 80 per cent of croup cases occurred during the Omicron period. Some cases were surprisingly severe, requiring hospitalisation and more medication doses compared to croup caused by other viruses.

"There was a very clear delineation from when Omicron became the dominant variant to when we started seeing a rise in the number of croup patients," said Ryan Brewster, first author and a from the Boston Combined Residency Programme in Pediatrics at the hospital.

Studies of Covid-19 in animals have found that the Omicron strain has more of a "preference" for the upper airway than earlier variants, which mainly targeted the lower respiratory tract. This may account for the sudden appearance of croup during the omicron surge, Brewster said.

In the first peer-reviewed report to date, physicians at the Children's Hospital describe 75 children who came to the hospital's emergency department (ED) with croup and Covid-19 from March 1, 2020 through January 15, 2022.

In keeping with the general pattern of croup, most of the children with Covid-19 and croup were under age 2, and 72 per cent were boys. Except for one child with a common cold virus, none had a viral infection other than SARS-CoV-2.

Although no children died, nine of the 75 children with Covid-associated croup (12 per cent) needed to be hospitalised and four of them (44 per cent, or 5 per cent of the total) required intensive care. (By comparison, before Covid, fewer than 5 per cent of children with croup were hospitalised, and of those, only 1 to 3 per cent required intubation.)

"Most cases of croup can be managed in the outpatient setting with dexamethasone and supportive care," Brewster said.

"The relatively high hospitalisation rate and the large number of medication doses our Covid-19 croup patients required suggests that Covid-19 might cause more severe croup compared to other viruses. Further research is needed to determine the best treatment options for these children."