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INVESTIGATION OF INFECTION IN IMMUNOCOMPROMISED PATIENTS

Over the past decade noticeable progress has been made in the management of the immunocompromised patient and better survival rates can be expected in conditions formerly associated with a high fatality, either as a consequence of the disease itself or from complications arising during its treatment. This improvement has seen the introduction of more intensive protocols both for the chemotherapy of haematological malignancy, and in preparation for bone marrow transplantation (BMT). These developments have led to a changing spectrum of infectious complications away from those caused by Gram-negative bacteria, which have traditionally been major pathogens in the neutropenic patient (Young, 1981), towards Gram-positive, fungal and viral infections (Watson, 1983). Also, the widespread use of long-term indwelling venous catheters has enhanced the pathogenic status of some species of coagulase-negative staphylococci, streptococci and corynebacteria, which formerly were often attributed with commensal status. Despite these trends, Pseudomanas septicaemia still carries a mortality rate of over SO% in the leukaemic patient (Singer, 1980). With this unsatisfactory ‘state of the art’ there is a continuing need to re-evaluate current and often expensive supportive measures (Rogers, 198 5). Accurate and reproducible methods for documentation of infection are of vital importance in this setting, and while culture and serological techniques have traditionally formed the mainstay of diagnosis they have failed to provide a means of ready and reliable confirmation of the presence of infection. This fact has increasingly focused attention on more rapid, direct and even ‘non-specific’ tests which might provide valuable guidance to management. The role of these investigations can best be assessed by considering a few scenarios which frequently occur and test combined clinical and laboratory skills. Fever during neutropenia. The onset of fever, without localizing signs of sepsis, is an almost invariable accompaniment to neutropenic episodes. In this event cultures of blood, urine, sputum and stools will be performed. Disappointingly, only a quarter of pyrexial episodes can be microbiologically documented (Pizzo et al, 1982a) yet the fact that fevers of unknown aetiology often respond fully to antibiotics strongly suggests that there are many occult infections in which the causative agent cannot be demonstrated by available methods. Blood cultures form a standard component of preliminary investigation prior to antibiotic administration. In an attempt to improve documentation it is not clear whether there is any advantage in taking repeated cultures rather than larger single samples of blood. Newer methods of processing blood cultures are under evaluation with the further hope that the time taken to confirm septicaemia can be reduced. These include automated systems either