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Annual report Surveillance of COVID-19, influenza and other respiratory infections in the Netherlands: winter 2021/2022.

Reukers, D.F.M., Asten, L. van, Brandsema, P.S., Dijkstra, F., Hendriksen, J.M.T., Hooiveld, M., Jongenotter, F., Lange, M.M.A. de, Teirlinck, A.C., Willekens, G., Meijer, A., Gageldonk-Lafeber, A.B. van. Annual report Surveillance of COVID-19, influenza and other respiratory infections in the Netherlands: winter 2021/2022. Bilthoven: National Institute for Public Health and the Environment (RIVM), 2022. 148 p. p.
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Each year, RIVM presents an overview of how many persons in the Netherlands got the flu and other respiratory infections. Since 2020, this report has also included an overview of how many people contracted the coronavirus.

During the summer of 2021, from July through September, very few people tested positive for SARS-CoV-2. These numbers increased during the autumn and winter with the rise of the Delta and Omicron variants. Between May 2021 and May 2022, 6,448,170 persons tested positive for SARS-CoV-2, of whom 44,990 were admitted to the hospital and 5756 were admitted to intensive care. 3482 persons are known to have died as a result of COVID-19.

Flu epidemic
The flu epidemic during the 2021/2022 flu season started later than in previous seasons and lasted 13 weeks. During this season, about 127,378 people went to their general practitioner with flu-like illness. This was less than in previous seasons, as most people with flu-like illness were tested for coronavirus and did not go to their general practitioner. An estimated 795,000 persons have had the flu between October 2021 and May 2022. They mainly became ill with type A(H3N2) influenza virus.

Since the spring of 2021, hospitals have been reporting high numbers of infections with RS-virus, particularly in the summer of that year. These infections mainly occur in children under four years of age. Most have mild symptoms, but the infection can sometimes be so severe that hospitalization is necessary. After the summer of 2021, the number of infections decreased, though it remained high enough to speak of an epidemic. This epidemic has been going on for more than a year. In total, hospitals reported 4504 RS-virus infections between May 2021 and May 2022.

Notifiable respiratory infections
Some respiratory infections have to be reported to the Public Health Services. When necessary, they can then quickly take action to prevent their further spread. The number of reported legionella cases (658) has increased sharply in 2021. The number of tuberculosis cases was higher in 2021 (680) compared to 2020, but still lower than in previous years. The number of psittacosis (parrot fever, 55) cases was significantly lower in 2021 than in previous years and the number of Q fever cases (6) was comparable to 2020, but also lower than in previous years. Q fever, psittacosis and legionella generally manifest themselves in the form of pneumonia. Persons with pneumonia are often not tested, so the causative pathogen remains unknown. The actual numbers are therefore higher than the reported numbers.