Pseudomonas occurs naturally in soil and water where organic matter decomposes. The Pseudomonas genus contains many species. P. aeruginosa is the most common. It lives in the intestines of approximately 10 percent of the population without causing disease. On hard surfaces, it can survive for months; humidity extends viability.
Symptomatic P. aeruginosa infection occurs most often when the body's immune system is compromised through injury or disease, such as severe burns, cancer, cystic fibrosis, severe chronic obstructive pulmonary disease, and acquired immunodeficiency syndrome. Infection sites include urinary tract, bone and joint, pulmonary, soft tissue and gastrointestinal areas. P. aeruginosa is resistant to many antibiotics and has a 50 percent mortality rate in severely immunocompromised patients.