Abstract Topic: 30. Infections in hematology (incl. supportive care/therapy)
Background: Bacillus spp. are Gram-positive, rod-shaped bacteria that are widely distributed in the environment. Although most cases of Bacillus spp. detected in blood cultures are considered as contamination, sometimes these species can cause serious infections and be fatal. Therefore, an early and useful indicator that distinguishes from other Gram-positive rods and enables to initiate the appropriate antibiotics is an unmet medical need.
Aims: To evaluate the characteristics of Bacillus spp. bacteremia in patients with hematological malignancies and find out clinical indicators that distinguish Bacillus spp. from other Gram-positive rods.
Methods: We retrospectively analyzed 130 patients with hematological malignancies treated at our hospital whose blood cultures were positive for Gram-positive rods between April 2012 and June 2022. In this period, Corynebacterium spp. was the most frequently detected species in blood cultures (n=82) and Bacillus spp. was the second most frequently detected species (n=29). Therefore, we compared these species to clarify the characteristics of Bacillus spp. bacteremia. Bacillus bacteremia was defined as a patient who had two or more positive blood cultures for Bacillus spp. or who had one positive blood culture and complicated with abdominal or central nervous system (CNS) symptoms which are associated with Bacillus spp. infection. On the other hand, Corynebacterium bacteremia was defined as a patient with two or more sets of blood cultures positive for Corynebacterium spp. Other cases not meeting the above criteria were defined as contamination. Moreover, time to positivity in blood culture (TTP) was defined as the time from the start of blood culture to the first detection of bacteria.
Results: Ten of 29 patients had Bacillus bacteremia (Bacillus cereus: n=9, Bacillus subtilis: n=1). All patients had fever, two patients had abdominal symptoms, and other two patients had CNS symptoms preceded by abdominal symptoms. All patients received sensitive antibiotics against Bacillus spp., and all patients inserted with central venous catheters (CVCs) had their CVCs removed. One patient died 9 days after the onset of bacteremia. White blood cell count of lower than 100/μL was identified as a risk factor to develop severe complications such as septic shock and CNS lesions (p=0.033). On the other hand, 42 of 82 patients had Corynebacterium bacteremia. (Corynebacterium jeikeium: n=7, Corynebacterium striatum: n=17, other Corynebacterium spp.: n=18). None of them presented with abdominal or CNS symptoms. Corynebacterium bacteremia was more common in male than Bacillus bacteremia (76.2% vs 20.0%, p=0.002). Moreover, the median TTP of Bacillus bacteremia was shorter than that of Bacillus contamination (5.35h vs 11.6h, p=0.0167), whereas the median TTP between Corynebacterium bacteremia and Corynebacterium contamination was not significantly different (21.4h vs 24.5h, p=0.0728). Interestingly, the median TTP of Bacillus bacteremia is significantly shorter than that of Corynebacterium bacteremia (p<0.001). When the TTP cutoff was set at less than 8.8 hours, the sensitivity and specificity for the diagnosis of Bacillus bacteremia were 90% and 97.5%, respectively.
Summary/Conclusion: Bacillus bacteremia is rare but can be fatal. Early diagnosis and treatment are important for improving the prognosis. Since Bacillus is detected earlier than Corynebacterium in bacteremia, TTP may be helpful for the diagnosis of Bacillus bacteremia. The larger scale studies are warranted to confirm these findings.
Keywords: Infection