The Hawaii Department of Health’s cluster report this week highlights an Oahu cluster that resulted from in-person employee training.

Health officials said they are now investigating a cluster from an employee training session in May that resulted in 35 COVID-19 cases on Oahu.

A total of 20 out of 41 employees that attended this training event tested positive for SARS-CoV-2, officials said. Another 15 secondary cases were also identified.

Two of the employees were hospitalized, and one required intensive care.

In addition, 12 training staff were also exposed to SARS-CoV-2 during the event, but all were vaccinated and tested negative.

Officials said COVID-19 mitigation measures were followed for most of the training sessions — including masking, 6-foot distancing, not congregating in common areas and eating meals outside.

But some parts of the training required physical contact and unmasked scenarios which brought employees and trainers less than 6 feet apart. The employees also reported additional exposure during transport to and from training sessions, and during social gatherings outside of training.

To prevent further clusters such as this, the Department of Health recommends encouraging or mandating COVID-19 vaccinations prior to training, and that mitigation measures be enforced during transport and social gatherings.

“Vaccination of employees and trainers can prevent COVID-19 transmission during employee training events,” said DOH in the report.

Another two-day employee training event on Oahu in June, before COVID-19 vaccinations were available, had resulted in a cluster of 44 coronavirus cases. That cluster lead to one death, and another employee that required intensive care.

On Oahu, health officials are also investigating a cluster from two social gatherings that resulted in 33 cases, one in the restaurants category that resulted in 13 cases, and one in the “other” category that resulted in 77 cases.

On Maui, a cluster in the travel, lodging and tourism category resulted in 33 cases, while two in construction and industrial resulted in two clusters and 26 cases, and on restaurant cluster resulting in six cases.

On Hawaii island, two small clusters are under investigation — one at a correctional facility, and one at an educational setting, with five cases each. Kauai County is investigating a construction and industrial cluster with just three cases.

Last week’s cluster report highlighted how the coronavirus can spread among construction workers when they travel and work in enclosed spaces with poor ventilation, or spaces where physically distancing is difficult. Since construction workers are considered essential, they are also exempt from Safe Travels quarantine requirements as they travel to and from work sites.

Also, construction workers removed their masks due to the heat and uncomfortable conditions inside buildings. This inconsistent use of masks and distancing, officials said, resulted in widespread transmission of SARS-CoV-2 among workers and their household members.

Vaccinations, too, would have helped prevent construction-related clusters, officials said.

The cluster report, released Thursday, summarizes cases that under investigation over the past two weeks.