Etiology of bacterial infections in febrile neutropenic patients: the role of the laboratory in the diagnosis

EPIDEMIOLOGICAL EVOLUTION: Until the mid-eighties, infectious complications (pneumonia, septicemia) observed in neutropenic patients were, in 70% of cases, of bacterial origin with Gram negative bacillae (Escherichia coli, Klebsiella sp, Pseudomonas aeruginosa) isolated 8 times out of 10. Among the Gram positive bacteria, Staphylococcus aureus predominated. The etiological profile of bacterial infections has since evolved with a predominance (60 to 70%) of Gram positive bacteria (coagulase-negative staphylococci, viridans streptococci) and a change in the epidemiology of the Gram positive bacteria notably with a lesser frequency of P. aeruginosa infections. THE GRAM POSITIVE BACTERIA: Coagulase-negative staphylococci are among the first germs responsible for nosocomial bacteremia (central venous catheters) and they are usually multiresistant. Viridans streptococci are a frequent cause of bacteremia; they are generally sensitive to antibiotics active on Gram positive bacteria, but the incidence of resistant strains is increasing. Enterococci are in majority responsible for colonisation in neutropenic patients and less frequently for infections; they raise the problem of resistance to antibiotics, notably to glycopeptides. Other Gram positive bacteria can be responsible for infections in neutropenic patients; it is crucial that they be identified because they require treatment with an appropriate antibiotic. GRAM NEGATIVE BACTERIA: Among the enterobacteria, Escherichia coli is predominantly isolated and raises the problem of the increasing incidence of resistance to fluoroquinolone. Pseudomonas aeruginosa, less frequently responsible today, remains associated with a far greater rate of mortality than that observed with the other microorganisms. Other Gram negative bacteria can be identified; they require an adapted antibiotherapy because they are often naturally multiresistant to antibiotics. THE ROLE OF THE LABORATORY: For the diagnosis of infections in neutropenic patients, the microbiology laboratory has a determinating role. The laboratory ensures the analysis of various biological examinations: blood cultures, methods permitting the diagnosis of an infection on a permanent catheter, copro-cultures (research for common enteropathogens, quantification in the case of digestive decontamination, screening for multiresistant bacteria), cytobacteriological examination of urine, samples of respiratory origin, cytobacteriological examination of cerebro-spinal fluid...).