Trends of Vancomycin-Resistant Enterococcus Infections in Cancer Patients

Objective Vancomycin-resistant Enterococcus (VRE) is an important cause of infection in immunocompromised populations. In Pakistan, very limited data are available regarding Enterococcus infection and its outcomes. We conducted this study to evaluate the trends including risk factors, treatment options, and outcomes of infections due to vancomycin-resistant enterococci in cancer patients in Pakistan. Methods We conducted a retrospective observational study. We extracted data from medical records of our center over a period of seven years. All admitted cancer patients with any vancomycin-resistant Enterococcus positive culture were included. The following parameters were evaluated: age, gender, type of cancer, febrile neutropenia, prior antibiotics, admission, comorbidities, system-wise infections (including bacteremia, catheter-related infection, pneumonia, urinary tract infections, intra-abdominal infection, bone and joint infections, skin and skin structure infections), intensive care unit admission, and 30-day all-cause mortality. Frequencies of infections, mortality, and drug susceptibility were evaluated over the course of seven years. Results Risk factors for enterococcal infection included prior exposure of piperacillin/tazobactam (n=209, 86.7%), meropenem (n=132, 54.8%), vancomycin (n=126, 52.3%), metronidazole (n=67, 27.8%), prior admission for more than 48 hours (n=198, 82.2%), and comorbidities (n=76, 31.5%), with acute kidney injury being most common (n=72, 95%) followed by diabetes mellitus (n=70, 92.1%). Precursor B cell acute lymphoblastic leukemia (pre-B ALL) was the most common malignancy in which infection occurred (n=54, 38.3%). Among patients who developed infection, 46% (n=111) had febrile neutropenia. Enterococcus species caused infection in 61% (n=147) and Enterococcus faecium in 39% (n=94). Bacteremia occurred in 45.2% (n=109) patients followed by urinary tract and intra-abdominal infection; 45.6% (n=110) patients were admitted to ICU, and 30-day all-cause mortality was 44.8% (n=108). Linezolid sensitivity was 100%. The total number of enterococci infections decreased over seven years. Frequency of E. species infection, bacteremia, intra-abdominal, skin-related infections, and recurrent infection also decreased, but the frequency of E. facium infections, ICU admission, and 30-day all-cause mortality was increased. Conclusion VRE infections have become less frequent but more severe in recent years with increase in mortality. Prior use of antibiotics (including piperacillin/tazobactam, vancomycin, carbapenems, and metronidazole), diagnosis of hematological malignancy, febrile neutropenia, diabetes mellitus, and renal failure are the risk factors for VRE infection. Bacteremia was the most common infection with high mortality rate. All strains remain sensitive to linezolid. Patients with these risk factors should be worked up for VRE and can be treated with linezolid empirically.


Introduction
Enterococci are gram-positive facultative anaerobic cocci that exist in short and medium chains [1]. They are usually found in the gastrointestinal tract and tend to cause serious disease in the immunocompromised or those with underlying diseases. The most common infections involve the urinary tract, wounds, and the bloodstream. Enterococcus faecalis (E. faecalis) is the most common species isolated, followed by Enterococcus faecium (E. faecium) [2]. All enterococci are intrinsically resistant to penicillins, cephalosporins, and carbapenems [3].
Vancomycin-resistant enterococci (VRE) are of six types: Van A, Van B, Van C, Van D, Van E, and Van G. Van A resistance phenotype has high-level vancomycin/teicoplanin resistance, and van B resistance phenotype has variable levels of vancomycin resistance but is susceptible to teicoplanin [4].
Quinupristin/dalfopristin and linezolid have emerged as approved therapeutic options for VRE [24,25,17], but quinupristin-dalfopristin has limited activity against VRE due to agricultural use of streptogramin and there is emerging linezolid resistance. Nitrofurantoin and fosfomycin are alternatives in uncomplicated VRE urinary tract infection. Daptomycin and tigecycline have shown excellent potential for treating VRE infection. Other treatment options include chloramphenicol, doxycycline, high-dose ampicillin or ampicillin/sulbactam, and nitrofurantoin (for lower urinary tract infection) [25].
We conducted a retrospective observational study to evaluate the risk factors and outcomes of VRE infections in cancer patients.

Materials And Methods
We conducted a retrospective single-center study at Shaukat Khanum Memorial Cancer Hospital and Research Center (SKMCH&RC), a tertiary care cancer center in Lahore, Pakistan. The study was approved by the Institutional Review Board at SKMCH&RC with a waiver of informed consent.
All registered cancer patients with a positive culture for VRE, from January 1, 2015, to December 31, 2021, were included in the study. Data were extracted from the online medical records. Patients were evaluated for fever and neutropenia. We also evaluated blood, urine, sputum or bronchoalveolar lavage, and other sitespecific pus or tissue cultures. Computed tomography (CT) scan of the abdomen and pelvis with contrast was performed for suspected intra-abdominal infections, with radiological guided pus aspiration if applicable. Magnetic resonance imaging (MRI) with contrast of the involved bone and joint was performed followed by radiological aspiration of fluid collections for involved joints.
All febrile patients were empirically treated with piperacillin-tazobactam. Patients with hemodynamic instability were started on empirical carbapenems. Empirical vancomycin was also added for patients with hemodynamic instability, chest X-ray consolidation, neurological symptoms, evidence of skin infection, and any central venous catheter in place. Cultures were followed for identification of organisms and sensitivity. Data on the following variables were included: age, gender, hematological or solid organ cancer, febrile neutropenia, antibiotics given within the last three months for more than 48 hours, details of isolates from positive cultures and their sensitivities, prior admission lasting more than seven days in last two months, any comorbidities, and any prior VRE infection. System-wise infections including bacteremia, catheterrelated infection, pneumonia, urinary tract infections (including catheter-or stent-related), intra-abdominal infection, bone and joint infections, skin and skin structure infections, intensive care unit admission, and 30-day all-cause mortality were also evaluated. Frequencies and proportions were reported for categorical variables. Mean and standard deviation were reported for continuous variables.

Results
A total of 241 patients were included in this study. The mean age was 32 years with a standard deviation of 23. There were 144 (59.75%) male patients and 97 (40.2%) female patients. Adult patients (aged more than 18 years) were 154 (63.9%) and children were 87 (36.1%). Hematological malignancies were diagnosed in 141 (58.5%) and solid organ malignancies were diagnosed in 100 (41.5%) patients. The most common hematological malignancy was precursor B cell acute lymphoblastic leukemia (pre-B ALL), which was present in 54 (38.3%), and the most common solid organ malignancies were breast cancer, urinary bladder cancer, and osteosarcoma, which were present in 11 (11%) patients each. A total of 111 (46%) patients developed febrile neutropenia after chemotherapy. Results are summarized in Table 1.    As far as sensitivities were concerned, 100% (n=241) VRE were sensitive to linezolid, 64.7% (n=156) were sensitive to chloramphenicol, and 18.3% (n=44) were sensitive to tetracycline. Results are summarized in Table 4.  CA lung -2 (6.5%) Frequency of fosfomycin and chloramphenicol sensitivity decreased from 20% to 15% and 62% to 54%, respectively, whereas sensitivity of tetracycline and nitrofurantoin increased from 8% to 31% and 12% to 19%, respectively. Results are summarized in Table 6.

Discussion
The results of our study revealed that the total number of patients with VRE infections has decreased but related ICU admission and mortality had increased in recent years. Most common infections were caused by E. species (n=147, 61%). VRE mainly caused infections in adults, and pre-B ALL was the most common malignancy. Other risk factors for VRE infection were febrile neutropenia, prior use of antibiotics, prior admission for more than seven days, and acute kidney injury. Bacteremia was the most common infection followed by UTI and intra-abdominal infections. In neutropenic patients, sinusitis was also reported (n=8, 3.3%). VRE infection led to 45.6% patients being admitted to ICU, with high 30-day all-cause mortality of 44.8% (n=108). All of the VRE isolates were sensitive to linezolid followed by chloramphenicol and tetracycline.
Similar to the results of prior studies, our study also concluded that bacteremia was the most common infection [19,20,25] followed by UTI and intra-abdominal infections [21,22] with high mortality rates of up to 57.1% [16]. All VRE isolates were sensitive to linezolid, thus making linezolid the drug of choice just like other studies [24,25,17].
There were some contradicting results as well. We did not find chronic obstructive pulmonary disease [7,9,11,14] as a risk factor for VRE. In our results, previous enterococcal infection occurred in only 10.8% (n=26) patients, whereas diarrhea [7,9,11,14] and Clostridium difficile infection [15] occurred in 1.24% (n=3) patients only. There were no patients with endocarditis [26]. Although nitrofurantoin and fosfomycin are alternatives in uncomplicated VRE urinary tract infections, their sensitivities were only 11.20% and 16.20%, respectively. Tigecycline has been reported to show excellent potential for treating VRE infection [25]; however, in our study, only 10.40% (n=25) VRE were susceptible to tigycycline, whereas 18.30% (n=44) were sensitive to tetracycline; 64.70% (n=156) isolates were sensitive to chloramphenicol [25], but its use is limited due to its toxicity. Being a resource-limited country, we do not have access to quinupristin/dalfopristin and daptomycin as treatment options for VRE. VRE without resistance to aminoglycosides can be treated with high-dose ampicillin combined with an aminoglycoside [27], making it a treatment option but requires further studies.
Major weaknesses of our study are its single-center nature and retrospective study design. We recommend further multicenter meta-analysis, retrospective case-control studies, and prospective studies for further VRE trend evaluation. The strengths of our study are the sample size and the study period spanning over seven years, in a region with minimal prior literature available on trends of VRE.

Conclusions
VRE infections have become less frequent but more severe with increasing mortality. Risk factors for VRE infection include prior use of piperacillin/tazobactam, vancomycin, carbapenems, and metronidazole, diagnosis of hematological malignancy, febrile neutropenia, diabetes mellitus, and renal failure. VRE bacteremia was the most common infection with high mortality rate of 44.8%; therefore, if patients with these risk factors develop fever, there should be a high suspicion of VRE infection, and they should undergo early workup. All VRE strains were sensitive to linezolid, thus making it an empirical drug of choice in lifethreatening conditions. However, further multicenter prospective studies are warranted to make treatment guidelines and further trends evaluation.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Institutional Review Board of Shaukat Khanum Memorial Cancer Hospital & Research Center issued approval EX-05-11-21-03. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.