A Decade of Details on Stenotrophomonas maltophilia

There are some microorganisms that are a cause for concern when they pop up on your laboratory report. Opportunistic infections especially make infection preventionists and medical providers alike worry about bigger issues brewing. Stenotrophomonas maltophilia is one such organism that has emerged as a multidrug-resistant opportunistic infection of global magnitude.

Growing incidence in both health care and community settings alike has worried researchers as this environmental bug has a propensity for respiratory tract colonization and infection.

Frequently found in more wet environments, but also animals, food, and water sources, such infections can impact organs and tissue alike. Sources of Stenotrophomonas maltophilia infections have included sink drains, hand-washing soap, contaminated disinfectants, nebulizers, and even hospital suction tubing. Additionally, showerheads and faucets tend to be a favorite hiding spot for the bug.

This organism has caused health care-associated infections and is also associated with high morbidity and mortality as it can prey on those with chronic or critical conditions. Those at an increased risk for infection can include people living with HIV, patients who have undergone organ transplantation, or individuals who have received prolonged therapy with broad-spectrum antibiotics.

Many working in infectious diseases have wondered how this organism has evolved over the years, both in terms of antibiotic susceptibility and prognostic determinants.

Researchers at the Mayo Clinic in Rochester, Minnesota, sought to address this very question by assessing 10 years of patients and data. By reviewing retrospective data from hospitalized adults at this facility, the researchers assessed the at-risk population, source of infection, common complications, antimicrobial susceptibility profiles, and clinical outcomes, to identify trends in over the course of a decade.

While Stenotrophomonas maltophilia is not an overly common organism, the investigators did find 98 patients to study. The most common source was found to be a catheter (63.3% of cases) and over 60% of cases were resistant to ceftazidime. The most common sources of infection following catheters were pulmonary (20 patients), gastrointestinal, urine, pleural fluid, bone marrow, and paranasal sinuses. Interestingly, in 40 patients (nearly 41%), blood cultures were polymicrobial, meaning they had co-infections. The most common being Enterococcus species (11 patients), followed by coagulase-negative Staphylococcus, and Escherichia coli.

Antimicrobial susceptibility assessments found that 2% of infections were resistant to trimethoprim-sulfamethoxazole (TMP-SMX) and 23% were resistant to levofloxacin. The study team compared these to other blood cultures during this time and found similar susceptibility.

The authors noted that “TMP-SMX remains the most appropriate empiric agent for treatment of S maltophilia infection because of its favorable susceptibility profile (98% isolates susceptible). In our cohort, we noted a concerning finding of increasing TMP-SMX MIC’s in a patient with recurrent bacteremia. As such, susceptibility to this drug needs to be confirmed, and not assumed for such patients”

When reviewing mortality data, the research team looked at all-cause in hospital mortality data, which found that 29 of the patients (29.6%) died and of those, over 50% had a pulmonary Stenotrophomonas maltophilia infection. Nearly 75% of patients were immunocompromised and most had an active malignancy, followed by 31% having a history of organ transplant. Additionally, 83.6% of those patients had a high ranking on the Charlson Comorbidity Index, with half requiring admission to the intensive care unit.

Overall, patients with Stenotrophomonas maltophilia are more likely to have comorbidities and thus catheters, which put them at an increased risk for infection. Understanding the antimicrobial susceptibility components and trends within patient demographics is important in reducing risk and increasing the chance for successful treatment.