Reports into Grand Millennium, Grand Mercure COVID-19 spread finds aerosol transmission likely to blame

"Aerosol transmission is regarded as the most plausible pathway."
"Aerosol transmission is regarded as the most plausible pathway." Photo credit: Getty Images.

Reports into COVID-19 transmission within two Auckland managed isolation facilities has found the virus was most likely spread via aerosol transmission.

Earlier this year, three workers at the Grand Millennium Hotel tested positive for COVID-19 while genome sequencing showed a link between two positive returnees at the Grand Mercure facility. There was also an incident in which a positive returnee was allowed on a bus ride to a walk, resulting in 14 others being considered close contacts.

In response, both hotels stopped accommodating new returnees and a review into the facilities was launched. 

The reports into both were released on Thursday and found that while it was not possible to absolutely conclude where and how transmission occurred, "aerosol transmission is regarded as the most plausible pathway". 

"We, along with the Ministry of Health, have taken a really close look at what went on with these cases in March and April, not least to see how we can strengthen the wider MIQ system," said the Joint Head of Managed Isolation and Quarantine Brigadier Jim Bliss.

"Each of the reports includes a number of recommendations for improvements, which are either complete or underway."

He said this includes emptying out both facilities and "completing full, on-site assessments of the ventilation at these sites". Both will remain unoccupied until such work is finished.

"A programme of extensive reviews and remediation of ventilation systems across all managed isolation facilities is underway. Remediation work at the Grand Mercure is almost complete. An extensive assessment of the Grand Millennium’s ventilation system has been done and a remediation plan is being developed."

At the Grand Millennium, the report found the virus most likely spread from the index case to Case A via aerosol transmission in a hallway and between Case B and C by direct exposure from two workers on the same shift. 

It emerged at the time that Case B hadn't been tested for serval months, leading to recommendations of improving barriers to staff testing and vaccination and continuing to improve data management systems.

A KPMG assessment of that incident found Case B provided inaccurate information to their employer. First Security, stating they had undergone each of their required tests. 

"KPMG noted that First Security developed systems and processes to keep and maintain records of border workforce testing and ensured resources were in place to operate the system. 

"The system and processes were aligned to the relevant duties in the Required Testing Order and duties under Health and Safety at Work Act to protect workers from harm."

It suggested making the Border Working Testing Register mandatory, which was done so in April.

In regard to the Grand Mercure incidents, the review found that while aerosol transmission via a fresh air supply cavity "seems unlikely", it is "nonetheless the most plausible transmission pathway between the index and secondary case.".

"The risk of downward airflow between rooms via the mechanism outlined by the ventilation experts, appears to be unique to the Grand Mercure Auckland. However, considering the range of IPC measures and mitigations in place, the overall risk of transmission to the returnees that were accommodated at the Grand Mercure, was low.

 "The review also found that a breach in bus protocols and non-compliance with the Standard Operating Procedures for the managed isolation walks programme led to the 14 returnees, classified as close contacts of the secondary case, staying an additional 14-day period in managed isolation. A breach in normal procedure resulted in the secondary case’s blue wrist band not being removed in error and this returnee attended a managed isolation walk when they should not have, later to return a positive COVID-19 test."

The Director-General of Health, Dr Ashley Bloomfield, is reassuring returnees that they can feel confident in the MIQ system, which more than 140,000 people have moved through over the last year.

"I want to reassure the New Zealand public that the overall risks to returnees of contracting COVID-19 within one of our managed isolation or quarantine facilities and taking it into the community has been, and continues to be, assessed by public health experts as very low."

He said there are "multiple layers of defence" at the border and inside MIQ to create safeguards to protect returnees as well as workers and the wider community. 

"That’s why so many people have been able to go through MIQ, with only a very small number of incidents such as these," he said.

"Where ever they occur, we investigate and make any required changes. As part of this process, the Ministry of Health undertakes regular infection prevention and control audits of the MIQ facilities, and any recommendations are actioned."