Cell-wall-deficient bacteria and culture-negative febrile episodes in bone-marrow-transplant recipients

Background Although about 75-80% of neutropenic fevers are thought to be ca used by infections, a causal organism can be confirmed microbiologically or suspected clinically in only 30-50%, and even fewer of these cases (16%) h ave a documented bacteraemia. The cause of neutropenic fever in the remaini ng cases remains elusive. We investigate the role of cell-wall-deficient ba cteria in bone-marrow transplantation (BMT). Methods Blood cultures were obtained from bone-marrow-transplant recipients and were inoculated into an aerobic bottle with resin, an anaerobic bottle , and a bottle to isolate cell-wall deficient bacteria. When growth was det ected in the blood-culture bottle for cell-wall-deficient bacteria, 20 muL of the broth was subcultured and the isolate identified by standard biochem ical methods. The microbiological findings were correlated with the clinica l characteristics of the patients. Findings From the 86 BMT recipients enrolled into the study, 798 sets of bl ood cultures were sent for laboratory analysis. 55 blood cultures were posi tive in the aerobic bottle, and the same isolates were also detected in 52 blood-culture bottles for cell-wall-deficient forms. For 20 sets of blood c ultures, the isolates were detected only in the bottle for cell-wall-defici ent forms. Blood for 13 (65%) of these 20 sets were sampled in the pre-engr aftment neutropenic period, three (15%) during conditioning when the absolu te neutrophil count was above 0.5x10(9)/L, and four (20%) in the post-engra ftment period. 17 (85%) of the isolates were gram positive: four (20%) were Staphylococcus spp and ten (50%) were Bacillus spp. Antibiotic treatment w as successful in 19 (95%) of 20 episodes. Interpretation Bacteraemia due to cell-wall-deficient forms causes a signif icant proportion of so-called culture-negative febrile episodes in BMT reci pients.