WHO: 23 Legionnaires' disease-related deaths in Poland since Sept. 11

A total of 166 cases of the disease have been reported, WHO said, adding that no new cases have been reported since Sept. 7.

Legionnaires' disease, caused by the legionella bacteria, can result in a severe form of pneumonia. The most common form of transmission is inhalation of contaminated aerosols produced in conjunction with water sprays, jets or mists of contaminated water sources, according to WHO.

In August, authorities said Poland's domestic security agency was investigating whether an outbreak of Legionnaires' disease might be the result of intentional tampering with the water system.

The infection source has not yet been identified and investigations are still ongoing to find the source of the outbreak, WHO said.

"Robust surveillance and response activities are being implemented during the current outbreak, and case numbers have been reduced. Nonetheless, without an identified source of Legionella bacteria, there is a continued risk of developing Legionellosis for people working or living in the affected areas. Older adults, smokers, and people with weakened immune systems are particularly susceptible to the disease," WHO added.

The organization also mentioned that "travel-associated Legionnaires’ disease (TALD) is a frequent phenomenon," adding that "about 20% of the cases of legionellosis detected in Europe considered to be travel-associated". "The outbreak is reported in the south-eastern city of Rzeszów, the main hub for humanitarian aid for Ukraine and the transit hub for international military support for Ukraine; therefore, TALD may be expected in people visiting Rzeszów."

WHO said that under current circumstances it recommends "the continuation of laboratory analyses, case identification and clinical care, contact tracing, outbreak investigation to identify the source(s), implementation of measures to prevent further infections, and enhancement of Infection, Prevention and Control (IPC) measures".

The organization does not recommend any specific different measures for travellers and advises against applying any travel or trade restrictions on Poland.