Investigation of Increased Rates of Isolation of Bacillus Species

BACKGROUND. In 2007-2008, several US hospitals reported summertime increases in the number of clinical blood cultures positive for Bacillus species, which are common environmental bacteria. OBJECTIVE. To investigate increased rates of isolation of Bacillus species from blood cultures, identify risk factors, and recommend control strategies. DESIGN. Survey and case-control study. SETTING. Multiple hospitals, including a cancer center. METHODS. We surveyed 24 facilities that reported increases. We also conducted a field investigation at a hospital with a high rate, reviewing charts, collecting clinical and environmental isolates, and observing infection control procedures. A case-control study compared inpatient case patients who had any blood culture positive for Bacillus with unmatched control patients who had a blood culture with no growth during June-August 2008. RESULTS. Among surveyed facilities, mean monthly rates rose from 25 to a peak of 75 Bacillus-positive blood cultures per 10,000 blood cultures performed during the period June-August. At the hospital where the case-control investigation was conducted, for most case patients (75%), the Bacillus-positive blood cultures represented contamination or device colonization rather than infection. We enrolled 48 case patients and 48 control patients; in multivariate analysis, only central venous access device use was significantly associated with case status (odds ratio, 14.0; P < .01). Laboratory testing identified at least 12 different Bacillus species (non-anthracis) among the isolates. Observation of infection control procedures revealed variability in central line care and blood sample collection techniques. CONCLUSIONS. Periodic increases in the environmental load of Bacillus species may occur in hospitals. Our investigation indicated that at one facility, these increases likely represented a pseudo-outbreak of Bacillus species colonizing central venous lines or their accessories, such as needleless connector devices. Vigilant attention should be paid to infection control practices when collecting blood samples for culture, to minimize the risk of contamination by environmental microorganisms.