AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Stenotrophomonas (Pseudomonas) maltophilia is an aerobic gram-negative bacillus that is found in various aquatic environments. It is an uncommon pathogen in humans.

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.

Pathophysiology

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.

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.

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.
• 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.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

• Because S maltophilia infections are extremely uncommon, no specific patient history suggests its presence other than contact with other colonized individuals.
• Obtaining a history of the use of irrigant solutions that could potentially contain S maltophilia is important in an epidemiological setting rather than in a clinical setting.

Physical

Signs and symptoms of S maltophilia infections are related to the organ system involved and are indistinguishable from infections with other pathogens.

Causes

• S maltophilia is a nonfermentative aerobic gram-negative bacillus formerly classified in the genus Pseudomonas. Unlike Pseudomonas aeruginosa, S maltophilia is an organism of low virulence with limited ability to cause infection in humans.
• S maltophilia is a water organism, and it survives and multiplies in aqueous environments, particularly respiratory secretions, urine, intravenous fluids, and irrigant solutions.
• S maltophilia may persist in an aquatic environment for extended periods.
• Sources of S maltophilia colonization include the following:
• • Personnel
  • • Hands
    • Antiseptic soaps
    • Hand lotion
  • Respiratory equipment and/or fluids
  • • Ultrasonic nebulizers
    • Inhalation medications
    • Respirator tubing condensate
  • Intravenous lines and/or fluids
  • • Intravenous solutions
    • Central venous catheters
  • Pressure monitoring devices - Pressure transducer fluids
  • Urine and/or fluids
  • • Indwelling Foley catheters
    • Urometers
    • Irrigation solutions

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

The main clinical problem presented by S maltophilia is failing to recognize its significance in the clinical context. The recovery of S maltophilia from respiratory secretions or from the urine of catheterized patients should be regarded as colonization until proven otherwise.

S maltophilia is a common cause of catheter-associated bacteruria in hospitalized patients. S maltophilia commonly colonizes the urine and is potentially pathogenic only in those with impaired host defenses, ie, patients with diabetes, systemic lupus erythematosus (SLE), cirrhosis, multiple myeloma, and those on steroids.

S maltophilia recovered from blood cultures may have come from contaminated intravenous fluids or from a distant infected source, eg, secondary bacteremia from the urinary tract in a patient who recently underwent instrumentation during a genitourinary (GU) procedure.

S maltophilia recovered from a wound with a clear or a serosanguineous discharge is of no clinical significance. If recovered from a purulent wound, S maltophilia may be the cause of the patient's wound infection.

The most common cause of confusion regarding S maltophilia is assuming that its recovery from body fluids implies a pathogenic role.

S maltophilia is a rare cause of nosocomial pneumonia in patients who are ventilated and presumed to have nosocomial pneumonia because of fever, pulmonary infiltrates, and leukocytosis.⁴⁰ The recovery of S maltophilia from respiratory secretions almost always represents colonization rather than infection, and its presence should not be addressed therapeutically.

Table 1. Hospital-Acquired S maltophilia Infections

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

Culture of the organism from body fluids and proper identification from the microbiology laboratory confirms the presence of S maltophilia. Usually, the presence of S maltophilia represents colonization. A potential pathogenic role must be evaluated by an infectious disease specialist. The mere recovery of a potential pathogen from any body fluid does not indicate a pathogenic role for the organism.

Histologic Findings

The histology of S maltophilia in the rare situations when it causes infection is indistinguishable from the histology of infections caused by other aerobic gram-negative bacilli.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

• Colonization of body fluids in hospitalized patients should be minimized if possible. Foley catheters should be used only as long as necessary and should be avoided if at all possible in immunocompromised hosts predisposed to urinary tract infections, eg, patients with diabetes, SLE, or multiple myeloma.
• Colonization of respiratory secretions in intubated patients in ICUs is the rule and is difficult to prevent.
• Patient-to-patient spread of organisms may be minimized or prevented by effective infection-control measures.

Consultations

A consultation with an infectious disease specialist is essential for differentiating colonization from infection in patients with S maltophilia isolated from various body fluids.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Because S maltophilia is predominantly a colonizer, antimicrobial treatment is unnecessary and may be potentially harmful.

As a general principle, colonization should not be treated with antimicrobial therapy.

S maltophilia, as a non–aeruginosa pseudomonad, is usually resistant to aminoglycosides, antipseudomonal penicillins, and antipseudomonal third-generation cephalosporins.

S maltophilia is consistently susceptible to trimethoprim-sulfamethoxazole (TMP-SMX). If TMP-SMX cannot be used, the organism is usually sensitive to meropenem, minocycline, respiratory quinolones, or colistin/polymyxin B. 

Drug Category: Antibiotics

Therapy must be comprehensive and cover all likely pathogens in the context of the clinical setting.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Deterrence/Prevention

• Because S maltophilia is a common nosocomial colonizer in patients and medical fluids, the recovery of S maltophilia should be considered nonpathogenic unless proven otherwise.
• If S maltophilia is recovered from several patients in the same area, sections of an ICU or ward can become the focus of further spread within the hospital setting.
• Effective infection control measures can minimize or limit the spread of this and other organisms in the ICU.
• Appropriate isolation procedures, rather than antimicrobial therapy, should be used to control the spread of S maltophilia.
• Medical personnel, including medical students, housekeeping staff, attending physicians, nursing personnel, and respiratory therapists, are potential carriers of the organism from patient to patient.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Clinicians often make the mistake of treating S maltophilia colonization with antibiotics. Except when the pathogenic role of S maltophilia is clear (ie, intravenous line sepsis secondary to contaminating infusions, colonization related to intravenous monitoring devices, urological instrumentation resulting in colonization), the mere presence of S maltophilia should not prompt treatment because it usually implies colonization rather than infection.
• The most common clinical pitfall with S maltophilia colonization is to treat it when the organism is recovered from urine. S maltophilia bacteriuria ordinarily should not be treated. In a patient with an indwelling Foley catheter, S maltophilia may be accompanied by pyuria, which represents colonization rather than infection unless recent antecedent urological instrumentation has been performed.
• The most common clinical error with S maltophilia colonization involves treating patients on respirators in ICUs because S maltophilia was recovered from their respiratory secretions.
• Because S maltophilia has not been reported to cause pneumonia except in rare cases involving cystic fibrosis or bronchiectasis, colonization should not be treated in patients who are ventilated, even if they have fever, pulmonary infiltrates, and leukocytosis.
• The needless and inappropriate treatment of S maltophilia with antibiotics may predispose patients to adverse drug effects, eg, drug fever or drug rash secondary to the sulfisoxazole component of TMP-SMX.
• The treatment of S maltophilia colonization may also predispose patients to fungal colonization or infection because of the selective pressures on the microbial milieu in the ICU.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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Article Last Updated: Jul 28, 2008