Background
Stenotrophomonas maltophilia, previously classified as Xanthomonas maltophilia, is an aerobic gram-negative bacillus prevalent in various aquatic environments. Although it is considered an uncommon pathogen in humans, there has been a notable rise in the recognition of S maltophilia infections, particularly in nosocomial settings (hospital-acquired infections). This organism is categorized as a nonfermentative gram-negative bacillus, distinct from the Enterobacterales family. Its increasing prevalence in clinical infections highlights the need for awareness and understanding of its role in healthcare-associated infections. [1]
S maltophilia is an organism of low virulence and frequently colonizes fluids used in the hospital setting (eg, hospital tap water, [2] 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 usually is incapable of causing disease in healthy hosts without the assistance of invasive medical devices that bypass normal host defenses. [3]
Risk factors associated with S maltophilia infection may include underlying malignancy, immunosuppressant therapy, cystic fibrosis, COPD, HIV, neutropenia, mechanical ventilation, prior colonization with stenotrophomonas, central venous catheter, genitourinary catheter, continuous ambulatory peritoneal dialysis (CAPD), recent surgery, trauma, prolonged hospitalization, ICU admission, and exposure to broad-spectrum antibiotics, third or fourth generation cephalosporins and carbapenems, and hyperalimentation. [4, 5, 6, 7, 8]
Pathophysiology
S maltophilia has few pathogenic mechanisms and, for this reason, predominantly results in colonization rather than infection. The main virulence factors that lend to disease pathogenesis include production of a variety of extracellular enzymes, evasion of host immune response, and triggering intense tissue inflammation.
When infections do occur, invasive medical devices often serve as the means by which the organism evades the body's normal defenses. Factors that facilitate the colonization of the respiratory tract or prosthetic devices—such as intravascular catheters, surgical catheters, and endotracheal tubes—include a cationic surface charge, flagella, and fimbriae, which aid in adhesion and biofilm formation. [43]
Epidemiology
Frequency
United States
S maltophilia is a noninvasive organism that has low virulence. It frequently colonizes body fluids but rarely causes infection (eg, intravenous line infections).
International
S maltophilia frequently colonizes the respiratory tract in patients with cystic fibrosis. [9, 10, 11, 12, 13]
The global pooled prevalence of S maltophilia is 5.3%, with a higher prevalence of 10.5% in the Western Pacific Region and a lower prevalence of 4.3% in the Americas. A meta-analysis indicated that the highest antibiotic resistance rate was against cefuroxime at 99.1%, whereas the lowest resistance was associated with minocycline at 4.8%. [14]
The prevalence of S maltophilia continues to rise; it has increased from 7% during 2004 - 2007 to 15% during 2020-2022. [44]
Mortality/Morbidity
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.
Likewise, in the urinary tract, the use of urologic irrigation fluids containing high levels of S maltophilia during invasive procedures, such as cystoscopy, can lead to gram-negative bacteremia. The associated mortality and morbidity from this condition are influenced by various host factors.
A meta-analysis identified key risk factors for mortality in patients with S maltophilia bacteremia. Out of 1248 patients analyzed, 506 (40.5%) died. Significant risk factors for mortality included ICU admission, septic shock, the need for mechanical ventilation, indwelling central venous catheters, neutropenia, comorbid hematological malignancies, chronic kidney disease, inappropriate antimicrobial therapy, and prior antibiotic use. [15]
The analysis concluded that appropriate antimicrobial therapy had a protective effect against mortality. Additionally, the presence of indwelling central venous catheters, neutropenia, hematological malignancies, and chronic kidney disease were associated with increased mortality risk.
S maltophilia bacteremia should be considered in patients with recent use of broad-spectrum antibiotics or recent isolation from any other site. The 30-day all-cause mortality rate associated with S maltophilia bacteremia (33.3%) is reported to be more than that of bacteremia caused by Pseudomonas aeruginosa (21.5%) and Acinetobacter species (17.3%). The independent factor associated with 30-day mortality was the SOFA score. [16]
Prognosis
The course of S maltophilia infection depends on the site of the infection, severity, response to antibiotics, and existence of other comorbidities. S maltophilia infections may be life-threatening, especially in immunocompromised patients. [17]
Tables
Infection |
Predisposing Factor |
Catheter-associated bacteriuria |
Indwelling urinary catheters |
Intravenous line infections |
Central intravenous catheters |
Urosepsis |
Urinary tract instrumentation |
Primary bacteremia |
Arterial monitoring devices |
Pseudobacteremia |
Contamination of blood during collection/processing of blood cultures |
|
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