An MBTA electric trolley bus.

THREE MBTA BUS DRIVERS operating out of the Cabot Garage in South Boston tested positive for COVID-19 on Tuesday, but the transit authority did not disclose the information until shortly after 1 p.m. on Wednesday, hours after news outlets began reporting on the story.

An MBTA press release provided no information on which buses the drivers were operating or whether riders on those buses would be notified in some fashion.

The T said the positive COVID-19 tests triggered facility maintenance protocols that require the transit authority to clean and disinfect all exposed employee work areas, vehicles, and equipment at the Cabot bus facility that the infected workers may have come in contact with.

“Through the public health tracing process, public health officials alert close contacts of the individuals who tested positive and will provide them with instructions for self-quarantine,” the press release said. “Under health information privacy laws, the MBTA is prohibited from providing identifying information about a particular employee’s medical status.”

The MBTA on Saturday started allowing passengers to board buses and Green Line and Mattapan trolleys at the rear door for free to minimize contact between riders and drivers. The T last week adopted new protocols calling for disinfecting all high-contact surfaces on buses during mid-day layovers, in addition to daily cleanings that take place on all MBTA vehicles and at four-hour intervals on high-contact surfaces in subway stations.

Jim Evers, the president of the Carmen’s Union, which represents the bus drivers, said his members are working with the T to ensure the health and safety of drivers. “But nothing is foolproof when interacting with the public every day,” he said. “Unfortunately, the T’s leave policies fall short of recognizing the sacrifice and dedication these employees are making every day on the job.”

Evers did not specify how the T’s policies fall short, but a spokeswoman said if employees need sick time they have to borrow it, or take an advance against future sick time.

Jim Aloisi, a board member at TransitMatters and a former state secretary of transportation, said after reading the T press release that the agency seems to be taking the right steps. He said the agency, like any other open to the public, will have employees test positive during the pandemic. “The cohorts of employees are too large to avoid any impact from virus spread,” he said in an email.

“The one thing I would be doing (if it isn’t happening already) is adding a screening protocol at the beginning of every shift, a screening that would include questioning each employee regarding their health ( I assume there is a standard checklist of questions that  the Department of Public Health can provide) as well as a non- invasive body temperature scan.  This will not identify asymptomatic people, but that is going to be true everywhere,” he said.

(This story is developing.)

Bruce Mohl oversees the production of content and edits reports, along with carrying out his own reporting with a particular focus on transportation, energy, and climate issues. He previously worked...