Harland and Wolff shipyard infection caused by metal fumes
Metal fumes caused a bacterial infection at Harland and Wolff shipyard in Belfast, the Health Minister said.
The Public Health Agency said the potentially deadly pneumococcal disease had been detected in a number of employees.
The bacteria can cause a variety of infections including pneumonia, meningitis and blood poisoning.
It is understood four staff were initially struck down, with tests carried out on others.
Health Minister Simon Hamilton said: "There is an accepted and acknowledged heightened risk for those who are welding of getting this disease from metal fumes. That is the believed source of this outbreak.
"We have been taking this matter incredibly seriously. Having identified those at risk we have been ensuring workers are provided with antibiotics."
Throughout Northern Ireland, there are around 50 to 60 cases of invasive pneumococcal disease each year.