New pathogens in neutropenic patients with cancer: an update for the new millennium.

As patients with malignant diseases are treated with increasingly potent agents it is likely that they will be subject to infection with an ever broadening array of microorganisms. As a result of the prompt institution of empirical antibiotics at the onset of fever in neutropenic patients, mortality has been reduced but new problems have emerged. First, there has been a shift in the type of infecting organisms responsible for bacteraemia in these patients from predominantly Gram-negative organisms to Gram-positive cocci. Secondly, perhaps as a consequence of the effectiveness of antibiotics, there is increasing concern about infections with antibiotic-resistant organisms. As an example, viridans streptococci are becoming increasingly resistant to penicillin. Thirdly, organisms previously thought to be non pathogens or 'commensals' are now being reported as agents of serious invasive infections in neutropenic patients with cancer. This review will highlight these changes and discuss 'new' pathogens in these patients.