Single-Institute Surveillance of Blood-Stream Infections by Stenotrophomas Maltophilia Among Patients with Hematological Diseases

Patients with hematological disease are often immunocompromised due to intensive chemotherapy, including hematopoietic stem cell transplantation (HSCT), and immunosuppressive therapy. Broad-spectrum anti-bacterial drugs were frequently given to those patients as an empiric therapy during a chemotherapy-induced myelosuppressive phase, which causes problematic emergence of drug-resistant strain and microbial substitution. Chemotherapy-induced disturbance of mucosa membrane barrier and skin barrier damage by central venous catheter (CVC) insertion gives pathogens an easy access to blood stream and a chance to develop blood-stream infections (BSIs).

Stenotrophomonas maltophilia (S. maltophilia) has been reported to emerge as frequent offenders of immunocompromised patients, especially those with hematological diseases and prolonged neutropenia. S. maltophiliais known to possess a high-level intrinsic resistance to variety of anti-bacterial drugs, including higher-generation cephalosporins and carbapenemes.

The aim of this study is to identify clinical characteristics of S. maltophilia BSIs such as drug sensitivity to properly treat immunocompromised patients with BSIs due to S. maltophilia.

This retrospective cohort study included all patients who admitted at department of hematology in our institute and from whose blood culuture (BC) or CVC culture (CC) S. maltophilia was isolated during 8 years from September 2003. Samples with positivity within two weeks are counted as a single case.

Among 5478 samples of BC and 258 samples of CC submitted to the laboratory, pathogens were isolated from 645 samples (11.8%) of BC and 74 samples (29.8%) of CC. Among positive samples, S. maltophilia was isolated from 52 samples (8.1%) of BC and 9 samples (11.7%) of CC. S. maltophilia was the third most frequent pathogens, next to Staphylococcus epidermidis (23.6% in BC, 29.9% in CC) and Candida (23.6% in BC, 29.9% in CC). This samples occupied 75.8% of 69 BC samples and 52.9% of CC samples among all S. maltophilia positive samples within our institute during the same period. Among these 61 samples, 60 samples (40 cases) were during treatment for hematological malignancies (25 cases AML, 8 cases ALL, 5 cases malignant lymphoma, one case MDS and multiple myeloma). 21 cases were in CR and 6 cases were after allogenic HSCT. Treatment before fever onset was; 6 cases allogenic HSCT, 14 cases AML type, 8 cases ALL type, 3 cases CHOP-like and 3 cases oral agents.

CVC was inserted to all patients except a MM patient. CVC culture was submitted in 18 cases of all BC cases and 7 cases (38.9%) were positive. Either BC or CC was positive in 31 cases and 3 cases, respectively. In 7 patients, repeated BC positivity was observed with interval from 22 days to one year 9 months (median 128 days).

Most cases were given higher-generation cepharosporins and carbapenems before fever onset, 12 case and 6 cases respectively. Before obtaining samples, cephalosporins and carbapenems were given to 25 cases and 20 cases, respectively. Treatment against S. maltophilia was; 17 cases drawal of CVC, 17 cases minomycline (MINO), 16 cases ceftazidime (CAZ), 10 cases quinolones, 6 cases SMX/TMP (ST) and 6 cases borad-spectrum drugs. Senvitivities of isolated S. maltophilia were; ST 61/61, MINO 61/61, quinolone (levofloxacin:LVFX) 60/61, CAZ 44/61. Only 2 cases (2 patients) died due to S. maltophilia BSIs.

Our data also shows that patients with hematological malignancies, especially AML and ALL, or after allogenic HSCT, are highly immunocompromised and predisposed to S. maltophilia. Althought high mortality rates around 20% among cancer patients with S. maltophilia infection are reported recently, our series shows only 5% of mortality. Recent resistance to those antbiotics, including ST, was reported but sensitivity test showed our series held high sensitivity to MINO/CAZ/LVFX. Our lower mortality rate could be due to treatment with CAZ/ LVFX. It is reasonable that those patients were still in neutropenic phase and needed be treated aganist other bacterium simultaneously. Although ST was given in only limited cases, none of isolates were resistant to ST. It might be important to identify sensitivities of S. maltophilia isolated in own institutes and choose sensitive agents when S. maltophilia might be a presumable pathogen.

No relevant conflicts of interest to declare.