The role of the internal ventilation system in a coronavirus outbreak at a nursing home in Maassluis was ‘downplayed’ by the public health institute RIVM, the Volkskrant said on Tuesday.

In addition, the RIVM was reluctant to issue warnings about the possible dangers posed by air conditioning systems which recirculate air, the paper said. The Volkskrant bases its claim on correspondence between the researchers and the RIVM.

Doctor and microbiologist Peter de Man, who was involved in the research, declined to comment on the correspondence but did tell the paper: ‘As a group of professionals, we are convinced that the virus was spread through the air, under the influence of the ventilation system.’

This, the paper says, is more concrete that the words which the RIVM used in the finalised report. It’s conclusions stated that ‘the combination of findings … suggests that the … virus may have been spread further by a ventilation system’.

The RIVM did, however, revise its ventilation guideline of July 28, stating that ventilation systems which recirculate air were not to be recommended, as a precaution.

In total, 17 of the 21 residents of De Tweemaster nursing home and 18 staff were infected with coronavirus in the space of three days, despite staff wearing surgical masks. Six residents died.

The safety of ventilation systems is particularly important because autumn is approaching, making infections in closed spaces more likely.