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Outbreak of COVID-19 in a Nursing Home Associated with Aerosol Transmission as a Result of Inadequate Ventilation

Our take —

In this letter to the editor, researchers described an outbreak among residents from a psychogeriatric nursing home in the Netherlands to explore the potential for aerosol transmission of SARS-CoV-2, which is of major public health concern. Researchers identified 17 residents (89% of 21 residents) and 17 healthcare workers (50% of 34 workers) who tested positive for the virus. They also found evidence of the virus in air conditioners on the ward and three of the ward’s eight ventilation cabinets. However, it cannot be determined whether, or to what extent, these cases occurred due to aerosol transmission or other routes of exposure, including surface contamination or non-aerosolized droplets spread between patients and staff who were permitted to be maskless during breaks and activities unrelated to patient care. Due to these and other limitations of the paper, results from this study should be interpreted very cautiously and a causal relationship between the virus in the ventilation system and the outbreak cannot be concluded.

Study design

Prospective Cohort

Study population and setting

The study objective was to measure an outbreak among residents and staff of a psychogeriatric nursing home in the Netherlands from June 23 to July 6, 2020. One of the seven wards had an outbreak among residents and healthcare workers. Residents and healthcare workers in all seven wards were tested for SARS-CoV-2 using reverse-transcriptase polymerase chain reaction (RT-PCR). Testing was also later conducted on the ventilation units of the ward with the outbreak but not the six other wards.

Summary of Main Findings

Of the 21 residents in the ward with the two-week outbreak, 17 (89%) residents and 17/34 (50%) healthcare workers tested positive for SARS-CoV-2. The median day of positive tests for residents was June 24, and for healthcare workers, June 26. The dust filters in the air conditioning units were tested on July 3, and one filter from the air conditioning unit contained SARS-CoV-2 RNA. The ventilation cabinet filters were tested on July 6, and SARS-CoV-2 RNA was detected on 3/8 (37.5%) samples. The ventilation system in the ward with the outbreak depended more on recirculating air from within the building as compared to the ventilation systems from the other six wards, which solely pulled from outside air. All residents (N=95) and staff (N=106) from the six other wards were negative for SARS-CoV-2. The researchers did not test for SARS-CoV-2 in the ventilation systems from these six other wards. The authors concluded that the outbreak was due to likely caused by aerosol transmission across the ventilation system because the outbreak was near-simultaneous, the level of cases in the surrounding area was low, and there were no cases in the other nearby wards, which used separate ventilation systems that depended on outside rather than recirculated air.

Study Strengths

The study pulled from multiple sources of data and observations to draw their conclusions, including RT-PCR testing of all residents and healthcare workers across all wards as well as testing of the ventilation system on the ward with the outbreak.


The authors presumed a causal relationship between the positive-testing ventilation system and the outbreak. However, the study also noted that healthcare workers did not wear masks when not engaged in patient care (i.e., breaks) and did not mention whether other social distancing measures or reduced visitation from outside family/friends occurred. Additionally, the ventilation systems of other wards were not tested, so it is unclear if the other wards had SARS-CoV-2 in circulation. Additionally, the filters were tested after cases occurred. Therefore, it is impossible to draw a causal relationship because the healthcare workers may have been infected from close physical contact with the clients, or vice versa, and all these infections could have occurred before the SARS-CoV-2 RNA was deposited into the ventilation system.

Value added

While the researchers could have provided additional evidence that would have cemented their conclusion, this study offered a compelling example of potential aerosol transmission in congregate settings (e.g., a nursing home).

This review was posted on: 20 October 2020