GNB bacteremia cases
During the study period, 929 patients underwent 1562 episodes of induction or consolidation chemotherapy. Among those patients, we identified 489 GNB bacteremia cases in 324 patients since 116 patients (35.8%) suffered from GNB bacteremia more than once. Among those cases, 122 (24.9%), 81 (16.6%), and 286 (58.5%) occurred during induction, re-induction, and consolidation chemotherapy, respectively. Of the total GNB bacteremia cases, 45 (9.2%) were carba-NS GNB and 444 (90.8%) were carba-S GNB.
Clinical characteristics of patients with carba-NS GNB bacteremia
The clinical characteristics of the two patient groups are described in Table 1. The age of patients with carba-NS GNB bacteremia was significantly higher than that of patients with carba-S GNB bacteremia (mean ± standard deviation: 56.4 ± 13.8 vs. 51.0 ± 14.8; P = 0.019). Male tended to be more frequent in carba-S group (59.2%) than in carba-NS group (44.4%; P = 0.056). The most frequent carba-NS isolates were Stenotrophomonas maltophilia (23 cases, 51.1%), Pseudomonas aeruginosa (11 cases, 24.4%), and Acinetobacter baumannii (10 cases, 22.2%). Among the carba-NS GNB bacteremia cases, 10 (22.2%) were polymicrobial infections.
Compared to the carba-S group, the carba-NS group showed significantly higher percentages of induction or re-induction chemotherapy, rather than consolidation (P < 0.001); isolation of VRE (P = 0.001), ESBL (P = 0.011), or CRAB (P < 0.001) in the prior year; preceding bacteremia during the hospitalization (P < 0.001); and carbapenem use at bacteremia onset (P < 0.001). In addition, the longer period from chemotherapy to bacteremia onset (P < 0.001), and the longer hospital stay (P < 0.001), significantly more carba-NS cases occurred.
Independent risk factors for carba-NS GNB bacteremia
A multivariate logistic analysis identified three independent risk factors for carba-NS GNB bacteremia. These risk factors were: carbapenem use at the onset of bacteremia (adjusted odds ratio [aOR]: 91.2, 95% confidence interval [95%CI]: 29.3-284.1, P < 0.001); the isolation of CRAB in the prior year (aOR: 19.4, 95%CI: 3.4-112.5, P = 0.001); and days from chemotherapy to GNB bacteremia (aOR: 1.1 per day, 95%CI: 1.1-1.2, P < 0.001; Table 2).
Independent risk factors for mortality
Carba-NS cases were significantly frequent in in-hospital mortality cases than in survival ones (21/63, 33.3% in in-hospital mortality vs. 24/426, 5.6% in survival; P < 0.001, Table 3). Carba-NS GNB bacteremia was independently associated with in-hospital mortality (aOR: 6.6, 95%CI: 3.0-14.8, P < 0.001) after adjusting with induction or re-induction chemotherapy rather than consolidation (aOR: 3.5, 95%CI: 1.7-7.0, P = 0.001), the isolation of VRE in the prior year (aOR: 4.3, 95%CI: 1.8-10.2, P = 0.001), pneumonia as a primary focus (aOR: 32.7, 95%CI: 5.1-208.5, P < 0.001), or the Pitt score (aOR: 1.5 per score point, 95%CI: 1.3-1.7, P < 0.001).
Also, compared to the survival group, the attributed mortality group showed significantly higher percentages of carba-NS GNB bacteremia (17/43, 39.5% in attributed mortality vs. 24/426, 5.6% in survival; P < 0.001, see Additional file 1: Table S1). Carba-NS GNB bacteremia was independently associated with attributed mortality after adjusting with clinical characteristics (aOR: 9.9, 95%CI: 3.5-27.7, P < 0.001).
To perform a subgroup analysis, we excluded all breakthrough GNB bacteremia cases that occurred during carbapenem use. Among these 459 cases, 20 (4.4%) were carba-NS and 439 (95.6%) were carba-S cases. Among the carba-NS cases, the most frequent carba-NS isolates were Stenotrophomonas maltophilia (8 cases, 40.0%), Pseudomonas aeruginosa (5 cases, 25.0%), and Acinetobacter baumannii (4 cases, 20.0%).
Univariate and multivariate analyses were performed to elucidate independent risk factors for carba-NS GNB bacteremia in this group of patients (see Additional file 1: Table S2). Independent risk factors for carba-NS GNB bacteremia without carbapenem exposure were the isolation of CRAB in the prior year and a time interval between chemotherapy and bacteremia. Carba-NS cases were also independently associated with in-hospital mortality in this subgroup (see Additional file 1: Table S3).