The microbiological epidemiology of PLA varies greatly by region. In Western countries, the main bacterium that causes PLA is E. coli.[3] In Chinese patients with liver abscess, KP is significantly more common than other strains.[4]
A total of 398 patients with PLA were enrolled in this study; 367 had a single bacterial culture of PLA, including KP (n = 292; 73.4%), E. coli (n = 25; 6.3%), and Streptococcus (n = 17; 4.3%). These results are consistent with previous studies on liver abscess tissue in Asia. The causes of PLA are diverse and include biliary calculus disease (cholecystitis, cholangitis), intra-abdominal infectious diseases (appendicitis, sigmoid diverticulitis, Crohn's disease), diseases after pancreaticoduodenectomy, liver transplantation, various postinterventional diseases, and/or liver trauma.[5]
In our study, the average length of stay was 12.61 ± 7.86 days. The main clinical symptom was fever (92.7%), and other symptoms included hepatic pain (22.6%) and nausea and vomiting (10.3%), which was consistent with European reports.[6] Among the combined diseases, 132 patients (33.2%) had hypertension, 132 patients (33.2%) had diabetes, 66 patients (16.6%) had fatty liver, 46 patients (11.6%) had liver cancer, 34 had biliary tract tumors (8.5%), and 25 had pancreatic cancer (6.3%). In addition, 57 patients had hepatic cysts (14.3%), 72 had hepatolithiasis (18.1%), 57 had cholecystitis (14.3%), 12 had cholangitis (3.0%), 13 had cirrhosis (3.3%), and 109 had a history of hepatobiliary surgery (27.4%). Cholelithiasis, biliary tract infection, and hepatobiliary surgery are all possible risk factors for liver abscess. The occurrence of PLA can be attributed to cholangitis associated with hepatolithiasis and cholangitis related to abnormal bilioenteric communication, such as hepaticojejunostomy or the presence of indwelling biliary stents.[7] According to some previous studies on PLA, diabetes has been regarded as a risk factor for PLA.[8] Chronic elevation of blood glucose in diabetic patients can result in an increase in plasma osmotic pressure, thereby inhibiting leukocyte chemotaxis, phagocytosis, and adhesion while also reducing immunity.[9] In addition, the majority of diabetic patients exhibit specific vascular lesions, resulting in reduced blood flow velocity and impeding the mobilization and movement of white blood cells, consequently rendering diabetic patients at high risk for BLA.[10] The average size of the PLA was 40.82 cm²±34.93 cm². The maximum diameter of the PLA at admission indicates a long hospital stay and poor prognosis. In patients with large PLAs, more aggressive treatment strategies coupled with vigilant monitoring are necessary.[11] When we suspect that a patient has PLA, the most commonly used auxiliary examination is abdominal US, which has the advantages of safety, low cost, noninvasiveness and practicality, with adequate sensitivity (ranging from 67–97%) for PLA diagnosis.[12, 13] CT has 95% diagnostic accuracy for PLA.[14, 15] A total of 38 patients were considered to have extrahepatic abscesses (9.5%), and the other abscesses were located in the biliary tract, abdominal cavity, thoracic cavity, subphrenic region, intracranial region, eye, brain, lung, subcutaneous region, prostate and so on. According to the correlation test between bacteria and liver lobe distribution in this study, there was significant positive correlation between KP and PLA in right lobe and negative correlation with PLA in left lobe and caudate lobe; E.coli was positively correlated with PLA in left lobe and negatively correlated with PLA in right lobe; and Streptococcus had a significant positive correlation with PLA in the caudate lobe and a significant negative correlation with PLA in the right lobe. Therefore, PLA in the right liver should first be considered KP infection, PLA in the left liver should be considered E. coli infection, and PLA in the caudate lobe should be considered Streptococcus infection. Clinicians need to empirically apply antibiotics to cover these common strains even before drug susceptibility testing results are available.
Our susceptibility data revealed that the percentage of ESBL-positive E. coli (44%) and the incidence of MDR E. coli (64%) were significantly greater than those of KP ESBL (7.2%) and KP MDR (7.9%). It is suggested that the probability of MDR and ESBL infection in E. coli is significantly greater than that in KP. In 50% of the patients, E. coli was resistant to cephalosporin antibiotics other than cefoperazone/sulbactam (8%), and the strains had the following resistance rates: piperacillin/tazobactam (24%), levofloxacin (52%), ciprofloxacin (48%), cotrimoxazole (44%), and ampicillin (68%). These results were similar to those of a multicenter study based on bloodstream infections.[16]KP is sensitive to most antibiotics except ampicillin (78.1%), which is slightly different from a previous report showing that KP was resistant to ampicillin in all cases (100%).[17] OGNB had a high drug resistance rate to β-lactam antibiotics and quinolones, and carbapenems or tetracycline antibiotics were selected according to the situation when the drug sensitivity results were available. The drug resistance rate of Enterococcus strains to β-lactams, quinolones and tetracyclines is high. Streptococcus species are resistant to erythromycin (25%) and sensitive to most other antibiotics.
Combined with the drug sensitivity results of this study and the expert consensus of PLA to discuss the empirical use of antibiotics, the Chinese Emergency expert consensus on diagnosis and treatment of bacterial liver abscess 2022, Expert Opinion 10, empirical antimicrobial drug selection and treatment course Article 2, which states that for patients with mild/moderate infection without MODS, a third-generation cephalosporin combined with metronidazole is preferred. β-lactam/β-lactamase inhibitors can be combined with metronidazole; Ampicillin can be combined with gentamicin and metronidazole.[18] It has been mentioned in the literature that KP is naturally resistant to ampicillin, with 100% susceptibility.[17] In our study, the drug resistance rate of the most common cultures of PLA were as follows: KP to ampicillin (78.1%), E. coli (64%), OGNB (68.8%), and Enterococcus (46.2%). Therefore, ampicillin is not suitable for first-line drug use in the Zhejiang region. Anaerobic bacteria and amoebic liver abscesses were not found in this retrospective study, and the incidence of these infections was low in Zhejiang Province, China. Amoebic liver abscess has varying degrees of incidence in France, Mexico, India, and the United Kingdom;[19–23] therefore, metronidazole may not be used in combination with other agents in patients with mild/moderate PLA infection without MODS.
E. coli should be considered in patients with left lobe PLA. In view of the resistance of E. coli to beta-lactams, clinicians should avoid the above antibiotics, which are associated with high resistance rates, and choose cefoperazone/sulbactam, carbapenems, and tetracycline antibiotics. For PLA in the right lobe, KP should be considered first. Clinicians should preferentially opt for cefoperazone sulbactam sodium or carbapenem antibiotics as the initial choice rather than ampicillin. The occurrence of PLA is predominantly observed in patients with biliary disorders or a history of malignancy who are infected by Enterobacteriaceae isolates producing extended-spectrum beta-lactamases.[24] For patients with a history of biliary tract disease or malignant tumor treatment, regardless of the location of the abscess in the liver, the use of carbapenems as a starting point plus linezolid or vancomycin is recommended. In patients with malignant biliary obstruction, antibiotic exposure predisposes patients to enterococcal bactibilia.[25] There have been reports of carbapenem-resistant high-virulence KP (Hv CRKP) strains in patients in East China, but the drug sensitivity analysis of the final study suggested that β-lactamase inhibitors, carbapenems, and fluoroquinolones are empirical choices.[26] ESBL-producing hv KPs are emerging, suggesting an urgent need to enhance clinical awareness.[27] The emergence of HV-KP has led to greater challenges for clinicians because the clinical manifestations of PLA are no longer the traditional manifestations of fever, abdominal pain, nausea and vomiting but can manifest as blurred vision, eye pain, etc., which can be metastatic lesions.[28] Clinicians need to view every infected patient with a broad view in actual clinical work and select effective antibiotics according to the actual condition.