Local health officials are dealing 15 cases of Legionnaires’ disease, a serious form of pneumonia that includes fever, coughing, chest pain, headache and other symptoms.

Six people have been hospitalized with the ailment in London.

The Middlesex-London Health Unit says the cases are linked to the south-central area of London.

The bacteria thrive in moist conditions and the health unit is investigating to identify the source.

Dr. Chris Mackie, the unit’s medical officer of health, says a normal year producers about six cases of the Legionnaires’ disease.

Mackie says most of the local people infected have a pre-existing illness. He says the best way for people to combat the disease is to remain healthy.