Stenotrophomonas maltophilia Infections in Geriatric Patients

We present Stenotrophomonas maltophilia infections in 317 hospitalized patients in a large health network over a 3-year period. The majority of patients were elderly. Most infections were polymicrobial: respiratory 95.2%, wound 91%, urinary 80.8% and blood 64.3%. Younger patients were small in number and were more common in those with otitis externa, infections from injection drug use and those with line infections. Most deaths were in patients with terminal conditions and polymicrobial infections and mortality could not be directly attributed to Stenotrophomonas maltophilia. None of the sputum, bronchial, urinary or wound culture positive patients had positive blood cultures. Only blood (14/317) or ear (7/317) culture positive patients had significant numbers of younger individuals with only 3 out of 14 over age 50 in blood culture positive patients and 1/7 in those with otitis externa. Those with bacteremia included patients with injection drug use, chronic pain syndromes and vascular catheter infections. 94% of urinary infections, 91.7% wound infections and 85.8% respiratory isolates were in those above age 50. Overwhelming majority of urinary infections were in males with drainage devices present in 75%. Recurrent infections were uncommon. Respiratory specimens were frequently associated with tracheostomies and endotracheal tubes. Most wound infections were in chronic lower extremity ulcers. Prior carbapenem use was not significant in this study. Isolates from all sites were over 98% susceptible to Trimethoprim/sulphamethoxazole. Limitations: The study group only had 1 organ transplant and 2 cystic fibrosis patients and no burn wound infections. © 2020 Don Walter Kannangara. Hosting by Science Repository. All rights reserved


Introduction
Stenotrophomonas maltophilia is a gram-negative bacillus known for inherent resistance to antibiotics, biofilm formation, association with carbapenem use, cystic fibrosis, hospital-acquired infections, burn wounds and immunocompromised [1][2][3][4][5][6][7][8][9][10][11][12][13]. In our study of 317 isolates, the majority were elderly (Table 1) except ear infections and infections in injection drug users and line infections. Most infections were polymicrobial ( Table 2). The wound infections were mostly chronic lower extremity infections. There was a clear association with Foley and suprapubic catheters, urinary stents, tracheostomies and endotracheal tubes. Very few patients received prior carbapenems. The attributable mortality was low in our study (Tables 3 & 4) in contrast to prior reports with rates as high as 37.5% [14,15]. Such overestimates are probably due to inadequate attention given to polymicrobial infections and serious underlying conditions (Tables 5 & 6) that contributed to deaths that were not adequately assessed.

Methods
We retrospectively studied 317 infections and clinical presentation of patients with laboratory reported Stenotrophomonas maltophilia positive cultures admitted to our health network during the 30 months ending in December 2018. The age of patients ranged from 1-98 (Table 1). The specimens were respiratory (105,62M/43F), wound (84,38M/46F), urinary (52,39M/13F), blood (14,7M/7F) and other sites. MALDI-TOF MS (matrix assisted laser desorption ionization-time of flight mass spectrometry) was used by the laboratory to identify the isolates. The charts were manually studied for the clinical presentation, sites of infections, prior antibiotic use, antibiotic susceptibilities and mortality.

V Other Infections
Seven patients had ear infections, 5 monomicrobial in contrast to polymicrobial predominance in other sites. Only one patient was elderly (age 74). Other patients were younger (ages 5,9,9,13,13,33) with otitis externa associated with swimming. Co-morbidities were not reported for any patient in this group.

Discussion
Our study shows that Stenotrophomonas maltophilia is predominantly found in elderly patients (Table 1) with the exception of bacteremia and ear infections. It is significantly associated with foreign materials such as foley catheters, suprapubic catheters, urinary stents, tracheostomies and endotracheal tubes. Monomicrobial infections were uncommon ( Table 2). S. maltophilia was almost always found in association with other organisms, most of which were more invasive (Tables 4, 5 & 7). Lack of invasiveness of the organism is seen by the absence of bacteremia in patients with urinary, respiratory and wound infections and absence of the organism in repeated blood cultures even with no treatment in some cases [18]. Majority of patients except those with ear infections had severe underlying diseases. Majority of urinary tract infections were in males due to higher number of male patients with drainage devices. The attributable mortality was low (Table 4) [18,19]. The organism was highly susceptible to TMP/SMX with > 98% with a minimal inhibitory concentration less than 2/38. For those who cannot tolerate TMP/SMX, levofloxacin is the best alternative. Ceftazidime or ticarcillin/clavulanate could be used if susceptibilities are known. In our series, respiratory isolates had the highest resistance to these two drugs (approximately 25%), but over half were susceptible at other sites. Prior carbapenem use was not significant in our patients.

Conclusion
The majority of Stenotrophomonas maltophilia infected patients were elderly (Table 1). Most infections were polymicrobial (Table 2). Many patients had serious underlying co-morbidities (Tables 4 & 6). The overwhelming majority of urinary infections were in males (39/52). Association with foreign materials was frequent in urinary (75%) and respiratory infections (53.2%) ( Table 6). Due to the association with serious underlying diseases and polymicrobial infections, only few deaths could be directly attributed to S. maltophilia (Tables 3, 4, 5 & 6). None of the patients with wound, urinary or respiratory isolates had a positive blood culture. Of 14 blood culture positive patients none had more than one positive culture. When the blood cultures were repeated, Stenotrophomonas maltophilia was not present with or without treatment. Prior carbapenem use did not play a significant role in our patients. The study limitations include low numbers of organ transplant (1) and cystic fibrosis (2) patients and no burn wound infections.