Stenotrophomonas Maltophilia in Hospitals

Stenotrophomonas Maltophilia is an uncommon bacteria with wide antibiotic resistance. Commonly found in aquatic environments, plants and soil, it can lead to a hospital-acquired infection in immunocompromised patients. Humid surfaces are a favorable environment for the bacteria to proliferate; they can ably colonize plastic or metal surfaces and infect the site of an indwelling urinary catheter or a tube used in mechanical ventilation. Cultures of lung or urinary specimen may yield an S. maltophilia growth, however, this is not definitive evidence of infection and results can prove difficult to interpret. Only S. maltophilia growth in a normally sterile environment (such as the blood) is indicative of true infection. Pneumonia, UTI or bacteremia caused by S. maltophilia is relatively uncommon (although all are possible), however, the incidence of pulmonary infections is increasing, as are colonization rates in those with cystic fibrosis. A wide variety of other infections has been associated with S. maltophilia, including COPD, soft tissue and skin infection, cellulitis, osteomyelitis, meningitis, and endocarditis.

This uncommon human pathogen generally displays low virulence. However, it is increasingly being recognized as an emerging global, opportunistic pathogen. Its multidrug resistance has been cause for concern, as is its significant fatality rate, as high as 69%. It has been suggested, however, that the mortality rate of S. maltophilia has been overestimated, with the actual cause of mortality being the underlying disease that gave way for the bacteria to colonize and infect the patient. Both nosocomial (hospital-acquired) and community acquired infections of S. maltophilia are on the rise. The prevalence of the bacteria in the sputum of cystic fibrosis patients increased from 6.7% to 12% between 1995 and 2005.

The bacteria was first isolated in 1943 and named Bacterium bookeri. It was listed to at least two other genera before its final classification in the 1990s.

Causes of S. maltophilia Infection

S.maltophilia can colonize fluids used and found in health care environments such as intravenous fluids, respiratory secretions, urine and irrigation solutions. If a patient's wound is irrigated with colonized solution, this allows the bacteria to bypass the body's natural defenses and cause infection. Generally speaking, S. maltophilia cannot infect healthy individuals without the aid of an invasive medical device.

S.maltophilia can also be transmitted to patients from the hands of health care workers. It is possible for the bacteria to be present in cough-produced aerosols of cystic fibrosis patients, which could lead to airborne transmission. Patient to patient transmission of S. maltophilia is generally uncommon, as is person to person transmission among healthy individuals. Patients who receive hematopoietic stem cell transplantation are seeing a greater incidence of S. maltophilia infections. The bacteria is generally only of concern when the patient is immunocompromised.

Symptoms of S. maltophilia Infection

It should be noted that S. maltophelia can colonize different parts of the body without causing issue or infection, in which case presence of the bacteria causes no symptoms.

There is a vast array of infections and disease that can be caused by this multidrug resistant bacterium in immunocompromised patients, and symptoms vary widely depending on the organ affected.

Conditions caused by S. maltophilia include:

  • bacteremia
  • UTI
  • endocarditis
  • respiratory tract infections
  • meningitis
  • typhlitis and biliary sepsis
  • skin and soft tissue infections
  • mastoiditis
  • bone and joint infections
  • peritonitis
  • typhlitis and biliary sepsis
  • wound infections
  • central venous catheter (CVC)-related infections

These conditions will generally produce uniform symptoms no matter which causative bacteria is behind them. Therefore, there are no symptoms unique to S. maltophilia infection. A specimen sample is required in order to determine what bacteria is behind the infection. Blood, urine, sputum, and mucus may be tested for the presence of specific bacteria, including S. maltophilia. When infection is suspected, possible infection sites like wounds, IVs, catheters and breathing machines may be tested for bacterial presence as well.

Risk Factors of S. maltophilia Infection

Many factors and conditions increase an individual's risk of developing S. maltophilia infection, such as:

  • admission to an intensive care unit
  • prolonged hospitalization
  • HIV infection
  • cancer
  • cystic fibrosis
  • neutropenia
  • recent surgery
  • trauma
  • mechanical ventilation
  • previous therapy with broad-spectrum antibiotics
  • urinary or veinous catheters
  • underlying malignancy

Thrombocytopenia (deficiency of platelets in the blood) has been identified as an independent risk factor for mortality from S. maltophilia infection.

A compromised immune system is the single greatest risk factor for developing S.maltophilia infection. When compounded with secondary factors like ICU admission, prolonged hospitalization, ventilation, catheter use or broad-spectrum antibiotic treatment, a perfect storm is created for colonization and infection by S. maltophilia.

Treatment of S. maltophilia Infection

Despite its multidrug resistance, there are still a handful of antibiotics available to treat S.maltophilia including:

  • ticarcillin-clavulanic acid
  • tigecycline
  • fluoroquinolones
  • polymyxin-B
  • rifampicin

Possible sources of infections should be promptly removed upon confirmation of bacterial presence, such intravascular catheters or ventilators. Novel therapeutic agents can be combined, such as aerosolized aminoglycosides and colistin. If applicable to the form of infection, in vitro active antibiotics may be used. Strict infection control measures can be implemented as well, both preventing the spread and advancement of infection in the patient and in the hospital setting/community.

Prevention of S.maltophilia Infection

Government studies have outlined at least 7 methods of S. maltophilia control and prevention:

  1. Education of health care staff about preventing the spread of this opportunistic organism and the conditions under which it can spread
  2. The aqueous-associated environments should be observed, cleaned and disinfected to ensure fluids do not become contaminated
  3. Hand washing hygiene should be meticulously reinforced
  4. Use of hospital tap water should be avoided for bathing and wound cleaning
  5. Residual fluids or antibiotic solutions should be immediately discarded and not used again
  6. Hospital equipment should be regularly cleaned and maintained, with worn and defective parts replaced
  7. Antimicrobial consumption should be well-controlled

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