Bacterial complications of transplantation: diagnosis and treatment.

Bacterial complications develop mainly after transplantation during the period before engraftment takes place. Wound infections, urinary tract infection and pneumonia are the commonest complications of solid organ transplantation and generally involve Gram-negative bacilli and Staphylococcus aureus. However, Gram-positive cocci will predominate when selective oral antimicrobial prophylaxis is given as is frequently the case in bone marrow transplant recipients. Oromucositis, induced by total body irradiation or anthracyclines, result in more bacteraemia due to oral viridans streptococci. The use of central intravenous catheters leads to an increase in bacteraemia and infection due to coagulase-negative staphylococci. Patients requiring intensive care are also at risk of nosocomial infections including legionellosis. Once engraftment has occurred, there is much less risk of bacterial infection but patients remain vulnerable to the intracellular pathogens Listeria monocytogenes, non-typhoid salmonellae, Norcardia spp. and mycobacteria for as long as they require immunosuppression. Any rejection crisis must be treated aggressively with high-dose steroids or other agents which further undermine an already fragile immunity. In bone marrow transplant recipients, graft versus host disease and its treatment exerts a more profound effect on immunity and often coincides with cytomegalovirus infection which compromises the patient even further. Such patients are again at risk of infection with the same range of pathogens encountered during neutropenia since the oral mucosa, gut and catheter, if one is present, provide the same portals of entry. Immunosuppressive therapy, in some centres, is discontinued once the risk of graft versus host disease is reduced, although the reconstitution of the immune system is a lengthy process and there is a continued deficiency of IgG which renders patients unable to opsonise the encapsulated bacteria Streptococcus pneumonia and Haemophilus influenzae. In contrast to bone marrow transplant recipients, those with a solid organ transplant require life-long immunosuppression and so remain susceptible to infections with intracellular pathogens and, even with minimal immunosuppression, there will always be the risk that common bacteria will cause infection in unusual places and that uncommon organisms will be involved in apparently straightforward infections.