Outbreak of pseudobacteremia with Bacillus species at a children's hospital traced to dust contamination of blood collection supplies on open shelving

BACKGROUND/OBJECTIVES: Numerous outbreaks of pseudobacteremia have been reported in hospitals, some of which were associated with Bacillus species. Between June and August 2004, an outbreak of positive blood cultures with Bacillus species was detected at a 255-bed tertiary children's hospital. The results of the epidemiologic investigation are reported. METHODS: Positive blood cultures were detected by routine daily microbiologic laboratory surveillance by infection control staff. The investigation included a clinical assessment of patients, evaluation of blood culture collection practices and supplies, an inspection of the environment where blood cultures were collected and phlebotomy supplies were stored, environmental bacterial cultures, and phenotyping of Bacillus isolates. RESULTS: Between June and August 2004, 12 patients had positive blood cultures with Bacillus species that were collected in the emergency room (ER). The cases represented a cluster compared to prior months, and none of the patients had “true sepsis.” Inspection of the ER environment found that supplies used to collect blood cultures were stored on an open shelving cart, that non-sterile blood-collection tube adaptors were stored in an uncovered bin on that cart, and that there was a very dusty air vent directly above the uncovered bin. ER staff in some cases would use a non-sterile blood-collection tube adaptor to collect blood samples for blood cultures, drawing blood directly into blood culture bottles. Bacterial cultures of the dusty air vent and the bin used to store the tube adaptors yielded two phenotypes of Bacillus species that matched six of the positive blood cultures ( B. sp. and B. cereus). Control measures implemented included cleaning of the dusty air vent, removal of the contaminated storage bin, storing of tube adaptors in plastic bags for dust protection, and implementation of sterile blood-collection tube adaptors for collecting blood cultures. CONCLUSIONS: • The probable source of the Bacillus pseudobacteremia outbreak was dust contamination of non-sterile blood-collection tube adaptors that occurred during unprotected storage on open shelving directly under a contaminated dusty air vent. • The probable mode of blood culture contamination was inoculation of blood culture bottles using a non-sterile blood-collection tube adaptor. • Storage of medical devices without dust protection on open shelving is potentially hazardous. • Air vents directly above open shelving storage of medical supplies should be kept clean.