Introduction:
Legionella pneumophila is frequently detected on various types of ships, particularly general cargo vessels. These environments are susceptible to Legionella proliferation due to diverse water sources, storage and distribution systems, variations in water temperature, and insufficient residual disinfectant levels. The World Health Organization¹ recommends controlling and preventing Legionella on ships, and the Portuguese Manual of International Sanitary Procedures² advises biannual water analysis for Legionella.

Methods:
This study describes the intervention by the Leixões Port Health Authority (LPHA) and the follow-up until 2024 on a cargo ship at the designated port of Leixões after the detection of Legionella spp. in 2022.

Results:
In February 2022, the LPHA inspected the ship to issue its Ship Sanitation Certificate, collecting water samples at two points for analysis. Legionella spp. and Legionella pneumophila (≥ 1 CFU/L) were detected at one sampling point. The LPHA recommended thermal shock, disinfection procedures and the creation of a water safety plan, as the ship did not previously have one. Follow-up testing in March revealed three samples with positive results for Legionella pneumophila (50 CFU/L, 130 CFU/L, and 200 CFU/L), leading to chlorination treatment of its two water tanks and other LPHA-recommended procedures. From April to June 2022, bimonthly control analyses were conducted at 12 points, all 12 samples returning negative for Legionella spp. From April 2022 to May 2024, 13 additional tests were performed, with all 13 samples negative for Legionella spp. Preventive actions were implemented, including the addition and control of disinfectant and sanitation plans in the water supply network.

Conclusions:
Regular water analysis on ships is crucial for preventing the spread of Legionella bacteria. Thermal shocks and chlorination are effective methods to eliminate Legionella spp. Establishing a reliable relationship between the ship’s crew and the LPHA enhances public health safety.