A pau hana gathering among construction workers, workplace training at Hawaiian Airlines, exercise in indoor gyms, birthday parties, barbecues and other social gatherings are to blame for a surge in coronavirus cases, particularly on Oahu.

Health investigations and contact tracing are “continuing to identify cases connected by gatherings or hanging out with close friends,” according to the state Department of Health, which reported 22 new confirmed COVID-19 infections Tuesday, 19 of them on Oahu and three on the Big Island. The new cases brought the statewide total number of infections since the start of the outbreak to 1,264.

The growing clusters are concerning health officials as public schools prepare to reopen on Aug. 4 and universities resume in the fall.

The DOH is working with University of Hawaii students on a communications campaign targeting young adults, who may not be following the rules. COVID-19 patients between the ages of 20 and 39 account for the highest number of infections — at more than 400 — but have the lowest hospitalizations at just 10. Details of the campaign are scheduled to be announced the first week of August.

“Our focus is on physical distancing, wearing masks and taking care of your mental health. Students will use social media, special events, and other platforms to share messages,” DOH spokeswoman Janice Okubo told the Honolulu Star-Advertiser.

Most of the 86 cases reported since last Friday are a result of clusters, including 44 related to a Hawaiian Airlines training event, where a single infected person spread the virus to dozens of others. That same person is also linked to a cluster of 20 cases at two undisclosed Oahu gyms. The airline conducted the training without physical distancing and mask wearing was optional, the Health Department said.

One construction worker attended a pau hana gathering while feeling ill and two gyms were small and poorly ventilated “without social distancing and use of face masks.” Meanwhile, parties, celebrations and faith-based home worship services caused significant illnesses. One individual attended a family barbecue despite having symptoms, ignoring the advice of health experts.

“Use physical distancing and wear a mask at small gatherings, remember smaller is better, and outside is better than inside. Do not attend gatherings when you are ill, stay home and self-isolate,” Okubo said.

The disease also has become prevalent in family clusters in Hawaii, where many live in multigenerational households. More children associated with adult cases are testing positive for the disease, the DOH said.

Currently, there are 321 active infections in the islands and a total of 921 patients now “released from isolation,” or about 73% of those infected. Hawaii’s coronavirus death toll remains at 22 — 15 of those deaths on Oahu.

Since the start of the outbreak, 133 have required hospitalizations, with five new hospitalizations on Oahu reported Tuesday, including two Hawaii residents who were diagnosed and treated outside the state. As of July 13, there were 23 people hospitalized for COVID-19.

Of the 97,557 coronavirus tests conducted so far by state and clinical laboratories, about 1.3% have been positive.

On Monday, Gov. David Ige announced a one-month delay to his plan to allow travelers who test negative for COVID-19 to forego the 14-day quarantine for trans-Pacific arrivals, following a spike in infections locally and on the mainland. The pre-travel testing program is now scheduled to start Sept. 1.