Leszek Szymański/PAP

The number of deaths from an outbreak of Legionnaires’ disease has risen to 18, health authorities in the south-eastern city of Rzeszow said in a statement on Thursday.

The statement added that nine men and nine women between the ages of 53 and 98 had died and that all had coexisting diseases.

The health department also confirmed two new Legionella infections within the past 24 hours. This means that at least 157 people have contracted the disease since the outbreak started.

Although an epidemiological investigation is ongoing, the source of bacteria has not yet been determined.

Legionnaires’ disease, caused by Legionella bacteria, is not contagious and cannot be spread directly from person to person, but can multiply in water and air-conditioning systems. Older adults, smokers and people with weakened immune systems are particularly susceptible to the disease.