BATH — A fourth city worker in Bath has tested positive for tuberculosis infection.

City Manager Duncan Ballantyne said Thursday that none of the city workers who tested positive can spread the disease.

“No one who has tested positive is a public health threat,” Ballantyne said. “No one is contagious.”

A positive test result indicates the person has been infected with TB bacteria. Only 5 percent to 10 percent of infected people typically become ill.

Ballantyne would not identify the city employees or their departments.

After three city employees tested positive for TB last month, Ballantyne offered TB tests to all city employees. About 85 of the city’s 105 employees were tested.

In 1989, more than 570 people tested positive for the disease after one case at Bath Iron Works went undetected for months.

Tuberculosis was once a major killer in the United States. It declined steadily in recent decades until 1985. Since then, the number of cases has increased 18 percent.