Stenotrophomonas maltophilia: Attributable mortality may be overestimated

Background: In prior studies the attributable mortality in Stenotrophomonas maltophilia (SM) infections, has been estimated as high as 37.5%. In our study of 107 respiratory isolates from hospitalized patients, majority, 100 (93.5%) were polymicrobial. The deaths were mainly in patients with terminal cancer, end stage chronic obstructive lung disease (COPD) and patients on hospice care. Other organisms in mixed infections were usually more invasive than SM. A high percentage had endotracheal tubes or tracheostomies. None had blood cultures positive for SM. Methods and materials: We manually reviewed charts of SM culture positive patients from different sites for 3 years ending in December 2018 from 10 hospitals in our network. There were 232 isolates of which 107 (50 M/47F) were respiratory; from sputum, bronchoscopy aspirates and tracheal aspirates. Only 16 patients were below age 50. We studied the clinical presentation, comorbid conditions, presence of endotracheal or tracheostomy tubes, prior antibiotic use, culture results, susceptibilities and mortality. Results: One hundred of the 107 (93.5%) specimens had polymicrobial flora. Thirty nine were on ventilators with endotracheal tubes and Seventeen had tracheostomies. There were 33 deaths. 32 of them had polymicrobial infections including 10 Pseudomonas aeruginosa, 1 methicillin susceptible Staphylococcus aureus, 2 methicillin resistant Staphylococcus aureus, 1 H influenzae, 3 Enterobacter cloacae, 1 Eschrichia coli, 2 Achromobacter xylosoxidans, 4 mixed flora and yeasts (C albicans +/- C glabrata), 7 SM + mixed flora, 1 Aspergillus fumigatus, 1 monomicrobial. Other organisms of significance in mixed infections of dead patients were M avium, Acinetobacter bereziniae, Klebsiella pneumoniae and Moraxella catarrhalis. 16 who died were on palliative care with no treatment.12 had terminal cancer,10 end stage COPD, 3 end stage amyotrophic lateral sclerosis, 2 ischemic bowel,1 anoxic brain injury and 1 with end stage muscular disabilities. All respiratory isolates tested (103/103) 100%, were susceptible to trimehoprim/sulphametoxasole with susceptibility to levofloxacin 98/103 (95.4%), ceftazidime 27/91 (29.7%) and ticarcilin/clavulanic acid 27/101 (26.7%). Conclusion: Majority of SM respiratory infections were polymicrobial, in elderly, with significant comorbidities, terminal illnesses and associated with endotracheal tubes and traheostomies in a significant number. Most deaths could not be directly attributable to SM.