Liver transplantation is currently the most effective treatment for end-stage liver disease. However, due to the long and severe course of the primary disease before transplantation, the complexity of the surgery, and the extensive use of postoperative immunosuppressive agents, postoperative infection has become an important factor affecting patient survival, especially the problem of fungal infection is becoming increasingly prominent. The incidence of fungal infections after liver transplantation has been reported in the literature to be as high as 5%-42%, with a morbidity and mortality rate of 11%-81%, much higher than acute rejection, renal failure and viral infection, and has become one of the important causes of graft loss and patient death.
Epidemiological features of fungal infections after liver transplantation
Fungal infections occur mostly within 2 to 3 months after liver transplantation and are rare within 1 week; the incidence is lowest after 6 months; and rebound after 1 year. Pulmonary infections are the most common, followed by abdominal, intestinal, biliary and urinary tracts. The pathogenic bacteria are more common, including Candida, Aspergillus, Trichoderma, Cryptococcus, etc. Candida is the most common, followed by Aspergillus. Pathogenic Candida is mainly Candida albicans, with the clinical application of antifungal drugs, non-Candida albicans has increased in recent years and drug resistance. Invasive Aspergillus infection is also on the rise, and the incidence of Aspergillus infection in liver transplant recipients is 1.5%-10%, with the lungs being more common and mortality rates as high as 70%-90%. Aspergillus can be lodged in the patient’s body via the respiratory tract, and when the host is immunocompromised, invade the tissue and cause infection. Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger are relatively common, Aspergillus fumigatus and Aspergillus terreus are less common. Pathogenic jointing bacteria are most common in Trichoderma spp. and can cause lung infection by blood or lymphatic fluid dissemination, followed by incisional infection. Pathogenic Cryptococcus is mostly new Cryptococcus, mainly invading the brain, followed by the lung. In addition, infections by S. multilocularis, Fusarium putrefaciens, Rhizoctonia, Coccidioides, and Pneumocystis carinii have also been reported. The common causative agent of early postoperative fungal infections is Candida, with Aspergillus infections predominating in the middle and distant stages, and Pneumocystis carinii and Amoeba infections occurring much later.
Risk factors for fungal infections
Fungal infections after liver transplantation are associated with the following factors.
(1) poor systemic condition of the patient before surgery. a Child score of C, low hemoglobin, granulocyte deficiency and thrombocytopenia, especially in patients with severe hepatitis, long-term hospitalization, decreased body resistance, and dysbiosis due to the use of multiple broad-spectrum antibiotics, as well as long-term indwelling catheters all increase the risk of fungal infections.
(2) Hepatopulmonary syndrome. Patients with end-stage liver failure are often combined with pleural and peritoneal effusions, pleurisy and peritonitis, and the translocation of flora leads to postoperative susceptibility to fungal infections.
(3) Hepatic encephalopathy. The presence of hepatic encephalopathy often indicates that the disease has progressed to the end stage, when the body’s immune function is low, endocrine disorders, systemic multiple organs or systemic dysfunction, intestinal flora displacement and endotoxemia occur, resulting in a higher rate of postoperative fungal infections.
(4) Preoperative infections. Especially viral infections, such as cytomegalovirus and human herpesvirus type 6, which have immunomodulatory characteristics, can reduce the body’s immunity and increase the risk of postoperative fungal infections in patients.
(5) Diabetes mellitus. the incidence was found to be 22.7% in a study by Faouzi et al. In a case-control study of liver transplantation, hyperglycemia was found to be a risk factor for Candida infection, with a morbidity and mortality rate of up to 81%. Another study showed that patients with post-liver transplantation Trichoderma infection had diabetes during the peri-transplantation period; (6) renal insufficiency or renal failure. Elevated creatinine levels and the need for perioperative hemodialysis are risk factors for fungal infections. a study by Kawagishi et al. found that patients treated with hemodialysis after living liver transplantation had a significantly higher rate of deep fungal infections than those who did not require hemodialysis.
(7) Surgery-related factors. including operation time of more than 12 hours, heavy intraoperative bleeding, massive input of blood products such as red blood cells, frozen plasma and cold precipitation; portal vein blockage time of more than 2 hours, performing biliary-intestinal anastomosis; surgical complications; dissection to stop bleeding; prolonged cold ischemia of the donor liver; and re-transplantation are risk factors for fungal infections.
(8) ICU-related factors: prolonged ICU treatment (>7 days); prolonged retention or poor drainage of various catheters such as urinary catheters, central venous catheters, gastric tubes, etc.; tracheotomy; prolonged use of tracheal intubation and ventilator; long-term parenteral nutrition, etc.
(9) Excessive use of postoperative broad-spectrum antibiotics and immunosuppressants. The risk of fungal infection can be greatly increased by excessive doses of postoperative immunosuppressive agents used to prevent acute rejection, low immunity of the patient, or prolonged use of broad-spectrum antibiotics to prevent bacterial infection leading to dysbiosis.
(10) Others. For example, transplanted liver failure, iron overload in the liver, postoperative pulmonary edema, and failure to clear potential infectious lesions may also be associated with fungal infections.
Diagnosis of fungal infections
Diagnostic criteria of fungal infection: patients with clinical symptoms of local or systemic infection and unsatisfactory antibiotic treatment; fungal culture or pathological examination by taking tissues or body fluids (including blood, sputum, urine, bile, abdominal drainage fluid, stool and intravenous catheter) from the relevant infection site, and any positive culture for >2 consecutive times or >2 places is diagnosed as fungal infection. Fungal colonization or skin fungi were not included in the statistics. Clinically, fungal infections are characterized by two high, two low and one fast, i.e., high infection and death rates, low clinical and laboratory diagnostic rates, and fast deterioration, and thus not easily diagnosed in a timely and accurate manner. The diagnosis of fungal infection after liver transplantation can be divided into three levels, namely, confirmed diagnosis, clinical diagnosis, and proposed diagnosis. The diagnosis is confirmed if the four conditions of risk factors, clinical features (including imaging), microbiology and positive histopathology tests of fungal infection are present at the same time; clinical diagnosis is made if the first three conditions are present; and proposed diagnosis is made if the first two conditions are present. In most cases, it is difficult to reach a definite diagnosis because histopathological diagnosis cannot be obtained in time, and clinical diagnosis is mostly based on clinical diagnosis. Due to the lack of specific clinical manifestations of fungal infection, some symptoms such as erythema nodosum, muscle nodosum, visual changes, thrombophlebitis, and neurological manifestations should also be taken seriously, in addition to the symptoms of upper respiratory tract infection.
Laboratory tests.
(1) Fungal smear, culture and histopathological examination are the main methods to confirm the diagnosis of deep fungal infection. In addition to the recipient body fluid, the removed catheter should also be used as the specimen for pathogenic examination. However, fungal culture has a low diagnostic rate, is time-consuming, and a single negative culture cannot exclude the possibility of infection. If necessary, tissue biopsy is feasible, and the diagnosis can be confirmed by observing fungal components on tissue sections, but it is more invasive and difficult to promote in clinical practice.
(2) ELISA, PCR and other new immune molecular biology methods can help early diagnosis and improve the diagnosis rate. The serum β-(1,3)-D-glucan test (G test) can diagnose deep fungal infection early, but it cannot be characterized and cannot detect cryptococcal infection; galactomannan antigen (+) (GM test) suggests Aspergillus infection, and it has been reported that the GM test has good specificity, but the sensitivity reports vary, ranging from 17% to 100%, which is more suitable for screening of Aspergillus infection in post-liver transplant patients, and continuous monitoring is needed to improve the sensitivity. The combined PCR-ELISA method for detecting fungal infections can help improve the diagnostic rate of fungal infections. Its sensitivity and specificity were 83.3% and 91.7%, respectively.
(3) The ATP assay of CD4+ T cells (ImmuKnow assay) provides a new reference in cellular immune surveillance after liver transplantation. Our recent study showed that the sensitivity and specificity of ImmuKnow low values in liver transplantation-associated infections were 85.3% and 76.3%, respectively. Its application in monitoring fungal infections needs to be further investigated.
Imaging: Aspergillus spp. multiplying in the blood can form clumps that block small arteries and cause tissue infarction, resulting in typical varicellar manifestations, especially in the lung and brain tissue. CT and MRI often show nodular lesions surrounded by faint halos and crescentic translucent areas and cavernous changes. Therefore, imaging has important diagnostic value for Aspergillus infection.
Prevention of fungal infections
There is a lack of a universally accepted prevention program, and it is extremely important to take active preventive measures throughout all aspects of the procedure to address the various high-risk factors that may lead to fungal infections.
(1) Adequate preoperative preparation. Improve preoperative anemia, low protein, and high bilirubin levels, enhance nutrition, and improve the patient’s tolerance for surgery. Narrow-spectrum antibiotics that are bacterially sensitive should be selected for patients with long-term hospital dependency.
(2) For patients with combined hepatopulmonary syndrome, aggressive treatment of preoperative thoracoabdominal fluid, improvement of pulmonary function, and strengthening of pulmonary function exercises.
(3) For patients with combined diabetes mellitus, they should be treated strictly according to the conventional treatment of diabetes mellitus and control postprandial blood glucose at 5-8 mmol/L.
(4) Actively treat renal insufficiency and prevent the occurrence of renal failure.
(5) preoperative iodophor and dacrynic acid skin rubbing, clean enema; careful intraoperative operation, fine anastomosis, avoid hepatic artery thrombosis and biliary complications, avoid secondary surgery; shorten the operation time and reduce the amount of surgical bleeding.
(6) Strengthen ICU management. Strengthen oral, respiratory and wound care; provide comprehensive and effective organ support; ensure unobstructed drainage, remove drains and deep vein catheters as early as possible after surgery depending on changes in condition; shorten the time of tracheal intubation, evacuate the ventilator as early as possible, avoid tracheotomy as much as possible, encourage patients to turn over and cough up sputum; strengthen environmental monitoring and disinfection, and perform protective isolation of patients to avoid cross-infection.
(7) For patients suspected of having viral and fungal infections before surgery, use antiviral and antifungal drugs postoperatively until the indicators turn negative; actively carry out mycological examination of various sites at an early stage, and strengthen the identification of fungi and drug resistance monitoring.
(8) Timely adjustment of the drug regimen of immunosuppressive drugs and prophylactic antibiotics after surgery. For patients at high risk of infection, non-hormonal treatment regimens should be used; certain immunosuppressive agents (e.g. primaquine) should be reduced or discontinued for those who have already developed infection or reduced white blood cells. The prevention of postoperative infections should be based on narrow-spectrum antibiotics and, as far as possible, on bacterial culture results to reduce the incidence of opportunistic infections and to discontinue them in a timely manner.
(9) Enhance early postoperative enteral nutrition. Since prolonged total parenteral nutrition can lead to atrophy of the intestinal mucosa and destruction of the barrier function, resulting in dysbiosis of the intestinal flora, creating conditions for fungal colonization and enteric-derived fungal infections, intestinal function should be restored as soon as possible after liver transplantation, which can reduce intestinal flora translocation and reduce the risk of fungal infections.
(10) In addition, patients should change their previous poor living habits after discharge, go to less crowded places, go to bed early and wake up early, wash hands regularly, pay attention to indoor environmental disinfection, and exercise moderately can reduce the chance of infection.
Treatment of fungal infections
Treatment of fungal infections after liver transplantation includes prophylaxis, empirical treatment, preemptive treatment and targeted treatment. Prophylactic treatment given to liver transplant patients with 2 or more high-risk factors can significantly reduce the rate of fungal infections. However, the optimal prophylactic medication, timing of use, and whether prophylactic antifungal therapy is routinely used are controversial.
Itraconazole and voriconazole are more effective than fluconazole and amphotericin B. The indications for empirical treatment are as follows.
(1) New fever (normal temperature or re-increase after having fallen) or persistent fever with elevated white blood cells.
(2) The presence of bacterial infections in the patient’s lungs, parenchymal organs, urinary tract, or incision.
(3) Poor efficacy after change of antibiotics.
(4) fungal and mycelial findings in the patient’s drainage fluid, bile, sputum and urine
(5) Patients with high-risk factors have fungi found at two sites more than twice at the same time. Early preemptive treatment should be used for those with high suspicion of fungal infection by imaging or early laboratory diagnostic techniques.
Targeted therapy should follow the three principles of removal of the infected site, adjustment of immunosuppression and antifungal therapy.
(1) Smooth coughing up of sputum and necrotic tissues is quite critical in pulmonary infections. Chymotrypsin nebulized inhalation or drugs such as amiloride can be used to dilute sputum, while care such as turning and patting the back and suctioning should be enhanced. The fungal plaque and necrotic inactivated tissues of the infected foci should be adequately removed for incisional infections. Brain abscesses should be surgically drained when conditions permit.
(2) Once a fungal infection is diagnosed, immunosuppressive drugs may be reduced or even suspended under the premise of ensuring that life-threatening rejection does not occur; (3) Antifungal drug therapy. In the case of clinically diagnosed fungal infection should be selected sensitive drugs, adequate amount, full course of antifungal drugs, and if necessary, combined therapy.
Classification of antifungal drugs.
① Polyenes: mainly amphotericin B and its lipid preparations. Its liposomes can reduce nephrotoxicity but do not improve the efficacy.
(ii) Pyrimidines: 5-fluorocytosine, used in combination with amphotericin B for the treatment of cryptococcal meningitis.
③Pyrroles: mainly include fluconazole, itraconazole, voriconazole and posaconazole. Fluconazole is mainly used for Candida albicans, but drug-resistant bacteria have been emerging; Itraconazole and voriconazole are effective for Candida albicans, some non-Candida albicans, and Aspergillus. Voriconazole can cross the blood-brain barrier and is superior to amphotericin B. Posaconazole can prevent Aspergillus and Candida infections and is also used for refractory Aspergillosis, Fusariosis and Sequamycosis. It is superior to fluconazole in preventing Aspergillus infections and reducing morbidity and mortality.
④Echinocandins: mainly include caspofungin, micafungin, anifungin, etc. Its hepatic and renal toxicity is small, suitable for serious Candida and Aspergillus infections, ineffective for Cryptococcus and Trichophyton. Special emphasis is placed on empirical treatment in antifungal therapy because fungal infections are difficult to diagnose, delayed treatment mortality increases significantly, and early empirical treatment can greatly reduce the morbidity and mortality rate.
Recent studies have shown that Cryptococcus novelis infection of the lung has an effect on immune function, mainly by enhancing the Th2 immune response to secrete large amounts of IgE, which leads to pulmonary dysfunction. Another study found that Aspergillus began to develop resistance to pyrrole antifungal drugs due to the widespread use of mycicides in the environment, and drug-resistant organisms are expected to continue to emerge.
Fungal infections have become one of the leading causes of death in liver transplant recipients. Familiarity with risk factors of fungal infections, effective prevention, early diagnosis, and aggressive treatment are important to reduce the prevalence and morbidity and mortality of fungal infections after liver transplantation.