Stenotrophomonas (Xanthomonas) maltophilia is an aerobic gram-negative bacillus that is found in various aquatic environments. Although an uncommon pathogen in humans, S maltophilia infection in humans, especially nosocomial, has been increasingly recognized.
S maltophilia is an organism of low virulence and frequently colonizes fluids used in the hospital setting (eg, irrigation solutions, intravenous fluids) and patient secretions (eg, respiratory secretions, urine, wound exudates). S maltophilia usually must bypass normal host defenses to cause human infection. For example, if an irrigation solution becomes colonized with this organism, irrigating an open wound can cause colonization or infection of the wound. S maltophilia is usually incapable of causing disease in healthy hosts without the assistance of invasive medical devices that bypass normal host defenses. 
Risk factors associated with S maltophilia infection have been defined and may include underlying malignancy, immunosuppressant therapy, cystic fibrosis, and exposure to broad-spectrum antibiotics.
S maltophilia has few pathogenic mechanisms and, for this reason, predominantly results in colonization rather than infection. If infection does occur, invasive medical devices are usually the vehicles through which the organism bypasses normal host defenses. Otherwise, the pathophysiology of this nonfermentative aerobic gram-negative bacillus does not differ from other nonfermentative aerobic organisms.
S maltophilia is a noninvasive organism that has low virulence. It frequently colonizes body fluids but rarely causes infection (eg, intravenous line infections).
Mortality and morbidity relate to the inoculum of S maltophilia that is able to bypass normal host defense mechanisms.
If an intravenous infusion contains large numbers of S maltophilia, then direct injection into the bloodstream may result in the signs and symptoms associated with gram-negative bacteremia.
Similarly, in the urinary tract, if urological irrigation fluids that contain large numbers of S maltophilia are used during an invasive urological procedure, eg, cystoscopy, then gram-negative bacteremia may occur with its attendant mortality and morbidity, which depend on host factors.