The report, published on Wednesday by the Dutch newspaper De Volkskrant and 1Vandaag, a current-affairs show, focused on a retirement home where in June almost an entire ward of patients was infected.

Despite wearing face masks continuously except for lunch breaks, 18 staff members were also infected. When a newly installed air-ventilation system was inspected, the health authorities found large quantities of the virus on the mesh covering air intake and extraction units and in its filters.

There is simply no other explanation possible, this is how everybody there got infected, all at the same time, through aerosols, said Maurice de Hond, a data specialist who has long criticized the Dutch health authorities for ignoring spread through aerosols. We need to realize this before autumn comes and more people will gather indoors.

It is unclear why the Dutch National Institute for Public Health and the Environment has kept its findings secret, but it did tacitly adjust the guidelines for ventilation, according to De Volkskrant. Three days after the report was released internally, the organization started publicly advising to avoid recirculation of air in spaces where several people are present, and refresh the air as often as possible.

Reporting was contributed by Maria Abi-Habib, Geneva Abdul, Hannah Beech, Emily Bobrow, Keith Bradsher, Luke Broadwater, Emma Bubola, Julia Calderone, Benedict Carey, Niraj Chokshi, Emily Cochrane, Patricia Cohen, Melissa Eddy, Thomas Erdbrink, Jacey Fortin, Sheera Frenkel, Maggie Haberman, Mike Ives, Cecilia Kang, Annie Karni, David Leonhardt, Patrick J. Lyons, Tiffany May, Giulia McDonnell Nieto del Rio, Constant Mheut, Sarah Mervosh, Saw Nang, Richard C. Paddock, Eileen Sullivan, Jim Tankersley, Pranshu Verma, Neil Vigdor, Sui-Lee Wee, Katherine J. Wu, Ceylan Yeginsu, Elaine Yu and Karen Zraick.

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Hours of Talks on U.S. Coronavirus Relief End With No Deal - The New York Times