At least 30 people who ride the bus from Modesto to Dublin have been tested for tuberculosis because a former passenger has the disease, health officials said Wednesday.

Stanislaus County public health workers have told passengers to get tuberculosis tests if they think they were exposed to the man, who was contagious during April and May. He is now recovering from the disease at his home.

The man's name has not been released. He rode the city's 5:20 a.m. BART Express bus from Vintage Faire Mall to the Dublin-Pleasanton BART station and took either the 5:45 or 6:30 p.m. bus back.

People who regularly rode these buses with the man have a slight chance of exposure to tuberculosis, which is spread through the air, said Cle Moore, associate director of the Stanislaus County Health Services Agency.

The risk is slight, Moore said, because people usually become infected after spending at least eight hours, day after day, in close quarters with a contagious person who coughs or sneezes. The ride to the BART station lasts one hour each way.

"They (commuters) are at very low risk," Moore said. "What we're doing is trying to educate them, trying to give them as much information as possible."

Tuberculosis, once the No. 1 killer in the United States, is caused by bacteria that often attacks the lungs. The disease is now prevented and cured with antibiotics.

There are 19 cases of active tuberculosis in Stanislaus County, including this latest one.

Many people harbor the bacteria, but never develop active tuberculosis, Moore said. Or, they may develop the disease years after being exposed to the germ.

That was probably the case with the man, believed to have been exposed to the bacteria seven years ago in the Philippines, Moore said.

The man was admitted to Modesto's Memorial Medical Center in late May for a variety of health problems, including diabetes. He was diagnosed with tuberculosis on May 27.

Public health workers immediately contacted the man's family members and close friends and gave them skin tests to detect the bacteria, Moore said.

A child who lives in the home and a social worker who works with children in the family tested positive, Moore said. However, they do not have active tuberculosis and are not contagious.

The child also may have picked up the bacteria in the Philippines, Moore said. Because the social worker is often around others in close quarters, it's not known if she was exposed to the bacteria in the man's home.

Public health nurses then turned their attention to passengers of the city's BART Express busses. On Tuesday, nurses and city workers rode the two evening buses to tell passengers they may have been exposed to the disease.

On Wednesday, nurses tested 30 passengers. The other 20-some passengers, Moore said, prefer to be tested at their doctors' offices. Results of Wednesday's tests will be given to passengers Friday.

Six bus drivers also were tested, Moore said. One driver tested positive, but does not have active tuberculosis and is not contagious. It's possible he picked up the bacteria somewhere else, Moore said.

Public health officials waited until this month to test passengers partly because the Centers for Disease Control and state Department of Health Services ask that workers first contact people with a high risk of contracting the disease, such as family members.

Also, it takes at least two months after being exposed to the bacteria for it to show up in tests, Moore said.

City bus officials are now preparing a list of regular riders so public health workers can determine who they've contacted.

"We owe it to our riders to alert them of the potential risk, even if it is low," city spokeswoman Renee Ledbetter said.

Bus passengers say they're glad officials informed them.

"It came as kind of a surprise," said Sandra Wilson, who lives in Modesto and takes the bus to BART. "But they gave us enough information to deal with it."

For more information about tuberculosis tests, call the Health Services Agency, 558-8866.