Article in Japanese

Pneumomediastinum and subcutaneous emphysema associated with influenza A/H3N2 virus infection

Maiko YAMASHITA^1）, Mitsumasa OSUNA^1）, Fumiko TANAKA^1）, Chiharu KAWAKAMI^2）, Miwako SAIKUSA^2）, Shuzo USUKU ^2）, Emi TAKASHITA^3）

This is the case of a previously healthy 5-year-old boy, who suffered from influenza A and was given oseltamivir on the 4th day of his illness. However, his fever was not resolved. He developed marked facial swelling on the 6th day of his illness and was hospitalized on the 7th. A contrast-enhanced computerized tomography (CT) scan of the neck, chest and abdomen confirmed extensive mediastinal emphysema and subcutaneous emphysema, extending from the face to the buttocks, and facial swelling was diagnosed due to subcutaneous emphysema. The fever and air leaks were alleviated by administering antibacterial agents and oxygen, and the boy was discharged on the 14th day of his illness. In this case, no existing risk of triggering air leaks such as trauma, cystic lesions or bronchial asthma, and no evidence of plastic bronchitis were found. However, A/H3N2 virus, which is a rare cause of air leaks, was detected in this case. Furthermore, this virus was an influenza A/H3N2 PAI38T mutant that exhibited reduced susceptibility to baloxavir, despite the fact that baloxavir marboxil was not used. It is considered that the air leaks occurred due to immature acquired immunity, because this was the case of a 5-year-old child who had never had influenza before. The mechanism to eliminate the virus takes time, prolongs airway inflammation, and increases airway hypersensitivity. It was inferred from the clinical course of this case, that A/H3N2 virus infection could trigger air leaks, and that this PA I38T mutant virus had the same infectivity and pathogenicity as the wild strain.

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1）Department of Pediatrics, Saiseikai Yokohamashi Nanbu Hospital
2）Yokohama City Institute of Public Health
3）Influenza Virus Research Center, National Institute of Infectious Diseases

Key words	mediastinum emphysema, air leak, influenza, barokisavir resistant virus, pediatric
Received	November 30, 2020
Accepted	April 13, 2021

33 (3)：217─224,2021