The Role of AC Systems in Nursing Home Superspreading Events

Nursing homes are the most common setting for superspreading events in the database. How can the virus spread so easily in them?

A confidential report of the Dutch scientific advisory board RIVM may provide an answer. It states that the HVAC system in a nursing home in the Netherlands likely caused an outbreak that infected up to 21 residents and 18 staff members.

Below is a (slightly manually improved) Google Translate of an article in Dutch newspaper De Volkskrant.

The main findings that are suggestive of aerosol transmission via the HVAC system:

- All staff members in the nursing home wore surgical masks (except during breaks)

- Only one patient was initially infected but the virus then spread rapidly throughout the facility

- The virus was found in high values ​​on the mesh covers of the air-conditioning unit and in filters of four ventilation cabinets.

Confidential RIVM report: ventilation system spread virus in nursing home

The modern ventilation system probably played a role in a corona outbreak in a nursing home in Maassluis. This is evident from a confidential RIVM report that is in the possession of de Volkskrant. The findings are the most persuasive evidence for the virus spreading through air circulation to date. RIVM has revised the ventilation guideline.

The confidential report fuels the ongoing discussion whether the covid-19 virus also spreads through the air (aerosols) through small particles. If that is the case, ventilation can play an important role. An open letter last month urged a group of 239 scientists to take this more seriously.

Between 23 and 26 June, 17 of the 21 residents in the De Tweemaster nursing home department were infected with the Covid-19 virus. Six of them died. 18 employees also contracted the virus, while staff wore surgical nasal masks, except during breaks.

However, when so many staff infestations abruptly occurred while only one patient was initially infected, the ventilation system in the common living room was investigated. The virus was then found in high values ​​on the mesh of the air-conditioning unit and in filters of four ventilation cabinets.

"The combination of findings (...) are suggestive for a further spread of the SARS-CoV-2 virus through a ventilation system," RIVM said in the confidential report, which was discussed at the institute on July 23. For the researchers involved, the finding is "reason to draw the attention of other institutions to the possible risks of ventilation systems with recirculation of indoor air".
Contradictory

The findings from the confidential report seem contradictory to what RIVM claims in public publications. For example, in response to questions from the Ministry of Health, the institute states that "there is currently no known outbreak in the Netherlands where it appears that (lack of) ventilation has played a major role in the transmission of SARS-CoV-2".

It is remarkable that RIVM tacitly revised the Ventilation Directive on this point last week, three days after reporting on the nursing home in Maassluis. It now states: "As a precaution, it is recommended to avoid recirculation within one room where several people are together for a longer period of time and to refresh the air sufficiently."

The relevant nursing home department has such a modern, energy-efficient ventilation system that circulates air in one room to prevent heat loss. According to the Argos Zorggroep, the location is now in use again. The care group does not want to explain how this relates to the stricter RIVM advice.

Branch association for elderly care ActiZ shared the amended RIVM Ventilation Guideline directly with its members last week, a spokesperson said. RIVM does not want to say why the amendment to the guideline has not been publicly communicated. Nor does it matter whether the case in Maassluis was the direct reason for the tightening.

"The RIVM does not make statements about confidential documents," is the formal response, although public documents also mention further research into the role of air recirculation within the common living room in "an outbreak in a nursing home in the Rotterdam region. ". The same applies to the role of air recirculation in "an outbreak in a meat processing company".
Aerosols

Professor of civil engineering at Eindhoven University of Technology Bert Blocken speaks of "a very interesting case". "This is, as far as I know, the first time in the Netherlands that the role of faulty ventilation in a mass contamination has been so carefully investigated and established." Blocken deliberately did not sign the aforementioned open letter, because it is not scientifically proven that aerosols and ventilation play a role play in virus transfer. "But it is becoming more and more plausible."

That is why the professor also considers it sensible that RIVM has amended the guideline. "This is progressive insight as we've seen over the past few months. Make sure ventilation is in order. That is still to be done. But that becomes a problem in the fall and winter. "
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