Microorganisms in Hospital Water Systems

There are a variety of microorganisms found in the water systems of hospitals; they include bacteria (Legionella pneumophila, Stenotrophomonas maltophilia, Pseudomonas aeruginosa), fungi (Aspergillus species, Fusarium species), and amoebae (Hartmanella, Naegleria, Acanthamoeba).  

Microorganisms in a water environment improve their chances of survival by a number of mechanisms, including attachment and multiplication in the biofilm (slime that lines pipes and fixtures) as well as living inside other microbes.

Microorganisms living inside amoebae can survive contact with chemical disinfectants and other harsh environmental conditions. These “amoeba-resisting microorganisms” include Legionella pneumophila (the causative agent of Legionnaires’ disease), Mycobacterium avium, and Pseudomonas aeruginosa

The microorganisms found in water are not generally pathogenic for healthy individuals, but may be pathogenic for the immunocompromised patient. These infections can result in significant morbidity and mortality.

Mortality of waterborne Pseudomonas aeruginosa pneumonia was estimated at 1400 cases per year. The conditions associated with increased risk of acquiring an infection from a waterborne pathogen include patients with hematological malignancy, immunosuppression (treatment with high dose steroids, chemotherapy), transplantation, and burns. Neonates are also at increased risk of infection following exposure to waterborne microorganisms.  

Water Sources that Transmit Infection

The types of water sources that can transmit infection vary from the simple use of tap water for drinking or rinsing medical equipment to contaminated medication vials (Table).  Exposure can occur via bathing (whirlpools), showering, drinking, direct contact with contaminated medical equipment (water baths) or bath toys. One of the most interesting developments has been the recognition that water systems are a source of infection by fungi (Aspergillus and Fusarium species), which have long been associated with airborne spread. 

Waterborne Pathogens and Sources of Transmission
within the Hospital Environment

Organism Site of Infection Sources of Infection
Pseudomonas aeruginosa Blood, catheter insertion site, lungs, urinary tract Potable water, contaminated liquid solutions and disinfectants, endoscopes
Stenotrophomonas maltophilia Blood (septicemia), pneumonia,
urinary tract, wound infections
skin, stools, throat,
trachea, urine
Potable water, distilled water, contaminated liquid solutions and disinfectants
Acinetobacter baumannii Skin, wound Room humidifiers, distilled water, moisture in mechanical ventilators
Chryseobacterium spp. Blood Potable water (burn unit), ice machine
Non-tuberculous Mycobacteria (NTM) species  (avium  and fortuitum) Abscesses and wound infections, disseminated Hospital hot water system, shower
Legionella pneumophila (other species rarely cause disease) Lung (pneumonia), sternal wound infection Hospital hot water system
Aspergillus species and Fusarium species Wound infection, disseminated disease Hospital water system