Infections after liver transplantation. An analysis of 101 consecutive cases

Liver transplantation

Liver transplantation has become an established form of therapy for patients with almost any type of irreversible and severe liver disease. The remarkable success of liver transplantation has resulted from recent advances in immunosuppressive therapy, surgical techniques, and patient selection. Additional progress has been made in the management of the complex postoperative medical complications that may occur. Indeed, liver transplantation has contributed significantly to an improved quantity and quality of life for many patients with liver disease.

Bacterial infections after liver transplantation

Infection is a common complication of orthotopic liver transplantations and a major cause of mortality. Of the different types of infection, severe bacterial infections are the most common. The majority (81%) of bacterial infections occur within the first two months after liver transplantation. The most frequent site of infection is the abdomen (intrahepatic or extrahepatic abscesses, cholangitis, and peritonitis). Bacteremia is a marker of mortality, and the majority of bacteremia cases are secondary to another bacterial infection site. The causative organisms vary among different centers. In some, gram-negative organisms are more common (66%); in one center, however, gram-positive microorganisms predominate (66%). In the latter center, the use of nonabsorbable antibiotics, which eradicate gastrointestinal aerobic gram-negative microorganisms, may explain this microbiologic difference. The main risk factor predisposing to bacterial infection appears to be the duration of the transplantation operation, especially beyond 12 hours. Of the deaths resulting from infection, 81% were caused by bacterial infection.

Aspergillosis

Aspergillus spores are ubiquitous in the environment and may become concentrated in hospital ventilation systems. Colonization in normal hosts can lead to allergic diseases ranging from asthma to allergic bronchopulmonary aspergillosis. Normal hosts rarely develop invasive disease, which is primarily an infection of severely immunocompromised patients. The major predisposing factors for infection include prolonged neutropenia, chronic administration of adrenal corticosteroids, the insertion of prosthetic devices, and tissue damage due to prior infection or trauma. Since Aspergillus spp. are respiratory pathogens, the most common form of infection is pneumonia followed by sinusitis. Patients with preexistant cavitary disease may develop noninvasive aspergillomas. Most infections are caused by Aspergillus fumigatus. The organism is capable of invading across all natural barriers, including cartilage and bone. It has a propensity for invading blood vessels causing thrombosis and infarction. The diagnosis of pulmonary infection is usually difficult to establish because the organism is seldom cultured from sputum and can represent contamination in some cases. Therapy is immunocompromised hosts is less than satisfactory and amphotericin B is the only agent with significant activity. There is anecdotal evidence to suggest that the addition of 5-fluorocytosine to amphotericin B may be beneficial.

Host-parasite interaction in fungal infections

The outcome of host-parasite interactions in fungal infections is determined by the balance between pathogenicity of the organism and the adequacy of the host defenses. A wide variety of host defense mechanisms are involved in protection against fungal infections. These include nonspecific mechanisms such as intact skin and mucus membranes, indigenous microbial flora, and the fungicidal activity of neutrophils and monocytes. Such mechanisms constitute the major host defense against opportunistic fungal infections caused by ubiquitous organisms of low virulence. The effective role of immunoglobulins and complement as opsonins varies with the fungal pathogen involved. Specific immune responses of both the humoral and cell-mediated type develop in response to infections by pathogenic fungi. Antibodies, in general, are not of major importance in protection against these infections. Specifically sensitized T lymphocytes produce lymphokines that activate macrophages. Activated macrophages are the major line of defense against systemic fungal pathogens. The type and degree of impairment in immune responses determines the susceptibility and severity of diseases. The type of immune response also determines the tissue reactions in these diseases and sometimes may be involved in the pathogenesis of the disease process. The role of natural killer cell activity, antibody-dependent cellular cytotoxicity, and biological response modifiers in various fungal infections has been described recently. The microbial factors of importance in fungal infections are adherence, invasion, presence of an antiphagocytic capsule, and ability to grow under altered physiological states of the host. The differences in the virulence of fungal strains is of minor importance in determining the outcome in general. The seriousness of the alteration of the host state rather than the pathogenic properties of the fungus determine the severity of the disease.

Cytomegalovirus infection in orthotopic liver transplantation

We retrospectively studied 175 orthotopic liver transplants in 151 patients. Of the 151 patients, 59 (39.1%) were diagnosed as having cytomegalovirus (CMV) infection. The rate of infection in patients treated for rejection was 48.8% as compared to 26.2% in patients without rejection (P less than 0.01). Antirejection therapy was associated with culture-positive cases in 33 out of 43 patients as compared to 9 out of 16 patients who had CMV antibody titer elevations. Patients were treated with gancyclovir if they had simultaneous positive cultures from multiple sites and were seriously ill. Eighteen of the 19 patients thus treated had side effects, one of which was serious (bone marrow hypoplasia). Cultures became negative in 15 out of 17 (88%) of the surviving patients. Patient survival was similar to our overall survival rate of 87%.

Liver transplantation

The 1-year survival rates of around 70% that are now being achieved have resulted in the acceptance of liver transplantation as a treatment for end-stage liver disease. The number of patients undergoing transplantation is increasing rapidly and the indications are widening. More patients are being transplanted for acute liver failure following the recent encouraging reports of successful grafting in this condition. The proportion of patients transplanted for liver cancer is falling as it becomes apparent that 80% of patients will die from recurrent disease. The selection of candidates and timing of transplantation continue to pose difficult clinical problems. Although the surgical and anaesthetic aspects of liver transplantation have been greatly improved, the 30-day mortality remains high at around 30% and postoperative complications, especially infection and rejection, continue to be major problems. However, rehabilitation is excellent for most patients and liver transplantation should no longer be considered an experimental procedure.