Open Access Open Badges Research article

Prevalence study of Legionella spp. contamination in ferries and cruise ships

Antonio Azara, Andrea Piana*, Giovanni Sotgiu, Marco Dettori, Maria Grazia Deriu, Maria Dolores Masia, Bianca Maria Are and Elena Muresu

Author Affiliations

Hygiene and Preventive Medicine Institute, University of Sassari, Sassari, Italy

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BMC Public Health 2006, 6:100  doi:10.1186/1471-2458-6-100

Published: 18 April 2006



In the last years, international traffic volume has significantly increased, raising the risk for acquisition of infectious diseases. Among travel-associated infections, increased incidence of legionellosis has been reported among travellers.

Aim of our study was: to describe the frequency and severity of Legionella spp. contamination in ferries and cruise ships; to compare the levels of contamination with those indicated by the Italian ministerial guidelines for control and prevention of legionellosis, in order to assess health risks and to adopt control measures.


A prevalence study was carried out on 9 ships docked at the seaports of northern Sardinia in 2004. Water samples were collected from critical sites: passenger cabins, crew cabins, kitchens, coffee bars, rooms of the central air conditioning system. It was performed a qualitative and quantitative identification of Legionella spp. and a chemical, physical and bacteriological analysis of water samples.


Forty-two percent (38/90) water samples were contaminated by Legionella spp.. Positive samples were mainly drawn from showers (24/44), washbasins (10/22). L. pneumophila was isolated in 42/44 samples (95.5%), followed by L. micdadei (4.5%).

Strains were identified as L. pneumophila serogroup 6 (45.2%; 19 samples), 2–14 (42.9%), 5 (7.1%) and 3 (4.8%). Legionella spp. load was high; 77.8% of the water samples contained > 104 CFU/L.

Low residual free chlorine concentration (0–0,2 mg/L) was associated to a contamination of the 50% of the water samples.


Legionella is an ubiquitous bacterium that could create problems for public health.

We identified Legionella spp. in 6/7 ferries. Microbial load was predominantly high (> 104 CFU/L or ranging from 103 to 104 CFU/L). It is matter of concern when passengers are subjects at risk because of Legionella spp. is an opportunist that can survive in freshwater systems; high bacterial load might be an important variable related to disease's occurrence.

High level of contamination required disinfecting measures, but does not lead to a definitive solution to the problem. Therefore, it is important to identify a person responsible for health safety in order to control the risk from exposure and to apply preventive measures, according to European and Italian guidelines.