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Annual report Surveillance of influenza and other respiratory infections in the Netherlands: winter 2019/2020.

Reukers, D.F.M., Asten, L. van, Brandsema, P.S., Dijkstra, F., Hendriksen, J.M.T., Hoek, W. van der, Hooiveld, M., Lange, M.M.A. de, Niessen, F.A., Teirlinck, A.C., Meijer, A., Gageldonk-Lafeber, A.B. van. Annual report Surveillance of influenza and other respiratory infections in the Netherlands: winter 2019/2020. Bilthoven: National Institute for Public Health and the Environment (RIVM), 2021.

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The flu epidemic in the winter of 2019/2020 was mild and lasted for 5 weeks. That is shorter than the ten-week average over the past 25 years. The last two weeks of the flu epidemic, the first half of March 2020, coincided with the start of the COVID-19 epidemic in the Netherlands. An estimated 400,000 people have had the flu between October 2019 and May 2020. About 74,000 people went to their general practitioner with flu-like illness.

People have mainly become ill with type A influenza virus. During the influenza epidemic, 600 more people died than would normally be the case. This “excess mortality” is probably related to influenza. Influenza vaccination prevented 48 percent of vaccinated persons from getting the flu. The effectiveness of the vaccine is about the same as in previous flu seasons.

COVID-19 epidemic in the Netherlands
This report includes the COVID-19 data for the duration of the flu season, up to and including May 17. The first COVID-19 patient in the Netherlands was confirmed on February 27, 2020. Since then, many people have been infected with the new coronavirus (SARS-CoV-2) that causes the disease COVID-19. Between February 27 and May 17, 2020, the Public Health Services reported 43,993 people with COVID-19, with a peak of 7,794 reports in the week of April 6. During this first wave, 11,095 patients were hospitalised and 9,600 more people died than expected in this period.

Notifiable respiratory infections
Some respiratory infections have to be reported to the Public Health Services in order to prevent any further spread. The number of reports of psittacosis rose sharply in 2019 to 91,
the highest number since 2010. The number of reported cases of legionella (566), tuberculosis (759) and Q fever (18) remained stable. Q fever, psittacosis and legionella usually manifest themselves in the form of pneumonia. The actual numbers are higher than the reported. People with pneumonia are often not tested, so the causative pathogen remains unknown.