Infections caused by Stenotrophomonas maltophilia (SMA) in patients in intensive care units: a prospective case-control study

Background and objective: The importance of Stenotrophomonas maltophila (SMA) as an etiologic frequently polyresistant pathogen in severe nosocomial infections has increased. Methods: In our prospective study we evaluated the risk factors of nosocomial infections by SMA in our internal intensive care unit (ICU) over a one year period from July 1997 to June 1998. Results: 111 patients (SO men, 31 women, mean age +/- SD: 58,0 +/- 13,3 years) were treated for more than 5 days in the ICU. SMA were cultured in 16/111 patients (13 men, three women, mean age 57,8 +/-3,4 years) out of bronchial secretions (68%), sputum (19%) and pleural fluid (13%). Univariate analysis resulted in 15 different risk factors (p <0.05); however, multivariate analysis provided three independent risk factors: chronic obstructive pulmonary disease (OR 95% CI [1.91; infinity]), length of stay in the ICU (OR 95% CI [1.07; 1.26]) and therapy with carbapenems before admittance to ICU (OR 95 % CI [0.56; 153]). Four of 16 patients died due to an SMA-infection, two by purulent exacerbations of a chronic bronchitis and two by sepsis. Molecular typing of 18 SMA isolates in 15 patients resulted in 9 different genetic types and a c[anal dissemination could only be confirmed in three patients. Conclusions: In respiratory ICU SMA infections are favored by severe COPD, length of stay in the ICU and by selection pressure of applicated antibiotics, especially carbapenems.