Waterborne Pathogen


Environmental Sources

Infection Sites

Modes of Transmission


L. pneumophila

Small (0.3–0.9 µm in width and approximately 2 µm in length) gram-negative rods with polar flagella. There are currently at least 58 species and over 70 serogroups, approximately half of the species have been implicated in human disease. Legionella pneumophila serogroup 1 is responsible for the majority of cases of Legionnaires’ disease; other serogroups and species account for less than 10% of reported cases of disease.

Building water systems including hot water, cooling towers, water features, spas, ice machines

Severe pneumonia

Aspiration or inhalation


A. baumannii

A. calcoaceticus

A. haemolyticus

A. johnsonii

A. lwoffii

These Gram-negative aerobic bacilli are generally considered nonpathogenic to healthy individuals. The settings for infection are usually medical or surgical intensive care units involving patients with preexisting conditions. Commonly found in fresh water and soil (moist and dry) environments. There are at least 23 species, with Acinetobacter baumannii accounting for about 80% of reported infections. Acinetobacter infections have increased and gained attention because of the organism’s prolonged environmental survival and propensity to develop antimicrobial drug resistance. 

Dry surfaces surrounding patient, hand carriage, medical equipment, humidifiers, ventilators, 

intubation, vaporizers, water baths, air

Ventilator-associated pneumonia; bacteremia. Respiratory infections; UTI; wound infection (including at catheter sites); septicemia

Direct, indirect and environmental contact; endogenous.


HAI from medical instruments and equipment


B. cepacia 

B. pseudomallei

An aerobic, non-spore-forming, Gram-negative rod found in water, soil and plants. Formally known as Pseudomonas cepacia, there are currently 20 species, mostly animal and plant pathogens. B. cepacia being of particular concern with respiratory infections in patients with cystic fibrosis. 

Potable water, ice machines, moist surfaces, medical equipment, cleaning solutions, distilled water, dialysis, nebulizers, water baths

Bacteremia; peritonitis; septic arthritis; respiratory infection; UTI



HAI may be caused by contaminated medical equipment and solutions


M. abscessus

M. avium

M. chelonae

These bacteria are small, rod-shaped acid-fast bacilli that are found in the environment, including soil, water, plants, animals, and water systems. These bacteria usually affect individuals with pre-existing conditions, specifically, lung disease, immunosuppression, transplantation and HIV infection. The most common infections are pneumonia and gastrointestinal disease caused by M. avium and M. intracellulare.

Potable water, ice machines, moist surfaces, medical equipment, dialysis, dental units, hydrotherapy tanks

Opportunistic infections in immunocompromised patients; pulmonary infection. Disseminated disease involving bone marrow, lungs, liver, lymph nodes, skin and soft tissue

Environmental contact, aspiration, or aerosolization


P. aeruginosa

This Gram-negative, motile, rod shaped bacterium can be found in various types of moist environments, including water and soil. This opportunistic pathogen is commonly associated with hospital-acquired infection, most notably in immunocompromised individuals. Pseudomonas aeruginosa accounts for up to 10% of all hospital-acquired infections. Notably, the pathogen can survive from six to 16 months on dry, inanimate surfaces in hospitals. Wastewater drainage systems have also been involved in infections. Healthy individuals can acquire eye, ear and skin infections through contaminated recreational waters such as hot tubs/whirlpool spas.

Potable water, ice machines, moist surfaces, medical equipment, dental units, dialysis, cleaning solutions, spas, pool, soil, fruits, vegetables, flowers

Ear, eye, endocarditis, respiratory tract, UTI, peritonitis, bacteremia

Environmental contact


S. maltophilia

These motile, Gram-negative non-fermentative bacilli were previously known as Pseudomonas maltophilia and Xanthomonas maltophilia and are common throughout the environment, particularly in soil and water. Individuals with existing conditions such as cystic fibrosis, immunosuppression, organ transplantation, malignancies, chemotherapy, prior broad-spectrum antimicrobial therapy, or presence of an indwelling catheter and respiratory therapy equipment are at highest risk of infection. Contaminated water or medical devices in hospital settings are the primary causes of infection.

Potable water, ice machines, moist surfaces, medical equipment, cleaning solutions, distilled water, dialysis, nebulizers

Bacteremia; meningitis; UTI; pneumonia; peritonitis; soft tissue, eye, wounds

Direct and environmental contact





These organisms are eukaryotic and filamentous. Of the estimated 250,000 species, fewer than 150 are known to be primary pathogens to humans. The presence of opportunistic molds such Aspergillus and Fusarium has been reported in hospital water and plumbing fixtures, however airborne spores are thought to be the primary mode of transmission with HEPA filters used to control airborne spores. Current guidelines do not recommend reducing patient exposure to water since its role in the spread of infections is unclear. Aspergillus and Candida are the most common invasive fungal infections with an
 80 to 90% mortality rate among severely immunocompromised.

Air, dust, moisture, water, construction materials

Soft tissue, burn-wound, respiratory

Direct and environmental contact