Non–C. difficile Clostridioides Bacteremia in Intensive Care Patients, France

Article Summary: This multicenter study focusing on critically ill patients showed a strong relationship between hemolysis and mortality.

O bligate anaerobic bacteremia is a rare event, accounting for ≈0.1%-10% of positive blood cultures; Clostridioides spp. bacteremia represents 8%-46% of the cases (1)(2)(3)(4). Clostridioides (formerly Clostridium) species are ubiquitous, gram-positive, spore-forming (most species), and toxin-producing bacteria (3). The most well-known toxins, C. perfringens α and θ toxins, induce platelet aggregation, diffuse formation of thrombi, cell lysis, and gas gangrene (5). Anaerobic bacteria are not only found in the soil or rotting vegetation but also are commensal constituents of the human microbiome, especially in the gastrointestinal tract or genital organs of women (3,6). Humans are usually infected by direct entry of the bacteria through a wound (C. tetani, C. perfringens) or by contaminated food (C. botulae). However, contamination of a wound by spores is not suffi cient to generate the infection because Clostridioides spp. need hypoxic and acidic conditions to proliferate. Conditions such as vascular trauma, atherosclerosis, or malignancies may induce tissue hypoxia. Moreover, the liberation of both α and θ toxin, which induce the formation of occlusive thrombi, may increase tissue hypoxia, sometimes leading to gas gangrene formation (3,(7)(8)(9).
Thus, Clostridioides infections are especially known to cause myonecrosis with rapid extension and gas gangrene formation, which, if not treated rapidly, may be fatal. This outcome has largely been described in the context of war wounds, trauma, and surgery (10)(11)(12). Although C. perfringens is mostly involved in gas gangrene, other Clostridioides subspecies can also be responsible for such infections (13).
Clostridioides bacteria can also cause primary bacteremia, with or without gas gangrene (2,6). Clostridioides bacteremia are usually fulminant and lifethreatening infections. Data focusing on Clostridioides bacteremia rely mainly on case reports (14)(15)(16), case series on selected populations (17,18), or larger epidemiologic series that contain microbiological data but few clinical descriptions (2,19,20). Although Clostridioides bacteremia often leads to sudden and massive organ failure requiring transfer to a hospital intensive care unit (ICU), no study has focused on Clostridioides bacteremia in the ICU . Therefore, we conducted a multicenter retrospective study of case-patients who were positive for all Clostridioides species except C. diffi cile to investigate Clostridioides bacteremia in the ICU; we described the clinical spectrum of critically ill patients, ICU admission conditions, microbiological characteristics, and outcomes. We aimed to identify risk factors associated with mortality.

Ethics
This study was approved by an Institutional Review Board (Comité d'Ethique de la Société de Réanimation de Langue Française no. CE-SRLF 18-38) in accordance with the French regulation on noninterventional studies, which waived the need for signed informed consent for patients included in this database. No data allowing identifi cation of the patients included in the study were recorded. The study was conducted in accordance with the Declaration of Helsinki principles.

Study Populatio n
We retrospectively recorded cases of Clostridioides bacteremia in the period July 2003-December 2018 in 15 ICUs in France. Patients were identifi ed by review of ICU medical records and hospital microbiological databases; we selected only cases with >1 positive blood culture for all Clostridioides species except C. diffi cile. Blood samples had been collected with specifi c anaerobic blood culture bottles and incubated in automated systems, in accordance with routine practice (21). Anaerobes were identifi ed using the API System (bioMérieux, https://www.biomerieux. com) until 2010; as of 2010, matrix-assisted laser desorption/ionization time-of-fl ight mass spectrometry methods were used in most of the centers to identify anaerobic bacteria (3,22). Antimicrobial susceptibility test results of Clostridioides species, evaluated by diffusion methods according to guidelines of the Comité Usually responsible for soft tissue infections, Clostridioides species can also cause bacteremia, life-threatening infections often requiring intensive care unit (ICU) admission. We conducted a multicenter retrospective study to investigate Clostridioides bacteremia in ICUs to describe the clinical and biologic characteristics and outcomes in critically ill patients. We identifi ed 135 patients with Clostridioides bacteremia, which occurred almost exclusively (96%) in patients with underlying conditions. Septic shock and digestive symptoms were the hallmarks of Clostridioides bacteremia in the ICU. We identifi ed 16 diff erent species of Clostridioides, among which C. perfringens accounted for 31% of cases. Despite the high sensitivity of Clostridioides to common antimicrobial drugs, mortality rates were high: 52% for ICU patients and 71% overall at 3 months. In multivariate analysis, the most important factor associated with increased risk for death was the presence of hemolysis. Clostridioides bacteremia often leads to multiple organ failures, which have high mortality rates.
de l'Antibiogramme de la Société Française de Microbiologie, were also collected for our study.
We reviewed ICU medical records of selected patients for age, sex, underlying diseases, clinical and biologic symptoms at ICU admission, the need for organ support, antimicrobial drug treatment, and outcome. We recorded Charlson index, simplified acute physiology score (SAPS2), and sequential organ failure assessment (SOFA) scores as previously defined (23)(24)(25). We defined septic shock according to the Sepsis-3 consensus definition (26) and hemolysis as low hemoglobin level associated with other hemolysis parameters, such as an increase of lactate dehydrogenase (LDH) or unconjugated bilirubin and reduced haptoglobin levels.

Statistical Analysis
We described categorical variables as counts and percentages and quantitative variables as median and interquartile range. We estimated mortality rate at 28 days and 90 days after the date of bacteremia, as a binary variable, and examined factors associated with overall survival as a time-to-event endpoint. We defined overall survival as the time between the date of Clostridioides bacteremia and the date of death or last follow-up, whichever occurred first. We performed survival analysis using a Cox regression model, estimating hazard ratios (HR) and 95% CIs. We checked the proportional hazards (PH) assumption and the log-linearity assumptions for the models; if the PH assumption was not valid, we used time-dependent coefficient for time-varying effect over time; we used a step function, with time-intervals defined based on the Schoenfeld's residuals. Factors which were associated to OS with a p<0.1 in univariate analysis were candidates for a multivariate adjusted model. We selected the adjusted model using a backward stepwise procedure, based on the Akaike criterion. All tests were 2-sided; p<0.05 was considered significant. We performed analyses by using the R statistical platform version 3.6.1 (https://www.r-project.org).

Documentation of Infectious Species
In total, 16 different Clostridioides species were identified by blood cultures, including C. perfringens in one third of the patients (Table 3; Figure 2). In univariate analysis, documented C. perfringens infection was not associated with a worse outcome than other Clostridioides species (HR 0.78, CI 95% 0.49-1.23; p = 0.285) (Appendix Figure 2). Blood cultures were mainly performed by peripheral venipuncture (58%), followed by central venous catheter puncture (23%) and arterial catheter puncture (17%). One blood culture revealed Clostridioides bacteremia in 87% of cases. Of note, 49 cases of Clostridioides bacteremia were polymicrobial bacteremia, yielding the presence of >1 type of bacteria in blood cultures, balanced between gramnegative, gram-positive, and other anaerobic bacteria. Nine patients had both gram-negative and gram-positive bacteria cultures. Hematogenous spread with gas-forming abscess was one particular complication, found in 9 patients and leading to death in 5 in the ICU (Figure 3, panels A-C). As suggested by clinical symptoms, cases of bacteremia were mostly from the gastrointestinal tract (74%), followed by myonecrosis (16%) (Figure 3, panels D-E). In total, 110 (91%) of the patients were treated with antimicrobial drugs in the ICU, and 64 (47%) patients underwent surgery that was mostly gastrointestinal surgery (67% of surgery interventions).
Most strains of Clostridioides were sensitive to β-lactam drugs. Clostridioides species were sensitive to clindamycin in 69% of the cases. Two species (C. tertium and C. septicum) were resistant to metronidazole. We did not find any association between specific antimicrobial agents used to treat Clostridioides bacteremia and mortality (HR 1.01, 95% CI 0.57-1.77; p = 0.977) (Appendix Table 2).

Outcomes and Mortality Risk Factors
Although Clostridioides spp. were for the most part efficiently treated by common antimicrobial drugs, Clostridioides bacteremia remained very aggressive and life-threatening; the overall mortality rate at 6 months was 71%. Of 135 patients, 84 died; 70 (52%) of all patients died in the ICU. The 28-day mortality rate was 55% (95% CI 45%-64%), and the 90-day mortality rate was 71% (95% CI 60%-79%). The rapid need for hospitalization after the occurrence of the first symptoms (median days 0, IQR 0-1) highlighted the aggressiveness of Clostridioides bacteremia; direct ICU transfer was necessary in most cases (median time between hospitalization and ICU transfer 0 days, IQR 0-2). Median length of stay in ICU was 2 days for patients who did not survive (IQR 1.25-5.75) and 11 days for survivors (IQR 5-23).
In multivariate analysis for overall survival, factors associated with increased risk for death were increasing age (in 5-year increments) ( On the other hand, male sex was associated with a reduced risk for death (HR 0.56, 95% CI 0.34-0.91; p = 0.02) (Figure 2).

Discussion
In our study, we found that Clostridioides bacteremia is an aggressive and rapidly life-threatening infec-  tion, occurring mainly in patients with underlying conditions. Septic shock with digestive symptoms is the usual manifestation. Despite rapid transfer to the ICU, large use of organ support, and active antimicrobial treatment, Clostridioides bacteremia remains highly lethal; 52% of ICU patients died. Massive intravascular hemolysis, associated with fatal complications, should alert clinicians to the possibility of sepsis. Data on Clostridioides bacteremia consist mainly of case reports (14)(15)(16)27) or case series that include a small number of patients (17,(28)(29)(30). Larger publications focusing on anaerobic bacteremia do not provide details on patients' characteristics and outcomes (2,19). Furthermore, we could find no previous publications on Clostridioides bacteremia in ICU patients, even though anaerobic bacteremia is frequent in this population (2,31). Our study provides a thorough description of the clinical and biologic characteristics as well as the outcomes of this serious condition.  Our results are consistent with earlier reports; most Clostridioides bacteremia cases occur in patients >65 years of age, and prevalence is higher in men (17,29,31). Diseases such as diabetes, chronic kidney disease, heart failure, and COPD, which maintain a baseline degree of organ ischemia and cause chronic organ failure, can lead to Clostridioides proliferation and consequently to bacteremia (1,19,29,31). Cancer patients or patients with hematological malignancies are also at high risk (18,32). Chemotherapy-induced cytopenia may result in neutropenic enterocolitis (33); this impairment of the natural digestive barrier favors the development of Clostridioides bacteremia. Digestive symptoms that have been described as hallmarks of this condition (1,17,29) were frequently associated with Clostridioides bacteremia in the ICU. Of note, although Clostridioides bacteremia is mostly from digestive origins, myonecrosis was identified as the origin of the bacteremia in 16% of the cases in our study, which is consistent with previous reports (17,18,29,31).
Among Clostridioides species, C. perfringens was more often identified as the source of bacteremia, as previously published (1,19,34). Fifteen other Clostridioides species have been identified; distribution is similar to the one described by Leal et al. (19). In this study, we chose to exclude C. difficile infections because this pathogen is mainly responsible for healthcare-associated digestive infections. C. difficile can still present as extradigestive infections; however, few cases of bacteremia have been reported (35,36).
Data on incidence of anaerobic and Clostridioides bacteremia are conflicting. Some authors report an increasing incidence of anaerobic bacteremia since the 1990s, whereas other report decreasing trends (2,6,20,37). The incidence of anaerobic bacteremia depend on patients' age and underlying conditions (especially cancer or cardiovascular illness), and antibiotic selection pressure driven by antimicrobial drug use and environmental conditions. In addition, as suggested by Morris et al. (38), blood cultures for anaerobic bacteria may be influenced by patients' background and clinical symptoms. Indeed, in a recent study evaluating anaerobic bacteremia, 39.7% of the positive blood cultures were considered to be bloodstream infections; the remaining 60.3% were attributed to contaminants (39). The evolution of microbiologic techniques, including growing use of automated techniques and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, might have also influenced the increasing isolation of anaerobic bacteremia. Although we cannot rule out that some infections may have been overestimated, the severity of clinical presentations in our cohort suggests that these cases resulted from true bloodstream infections.
Of note, Clostridioides bacteremia can present either as a single microbial bacteremia or as a polymicrobial bacteremia (2,28,30,31). Enterobacteriaceae were the most commonly associated bacteria, followed by Staphylococcus species. Cultures for multiple microbes were positive for Clostridioides spp. in 18 patients. Comparable results were also found by Fujita et al. (17). Clostridioides species are largely susceptible to common antimicrobial drugs, except for clindamycin; susceptibility for clindamycin has been reported as reduced by 73%-96% (1,3,5,19,31). High susceptibility to penicillin should alert clinicians to rapidly initiate treatment in identified cases of Clostridioides bacteremia.

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Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 27, No. 7, July 2021 Because 94% of the patients in our study received adequate antimicrobial drugs within 24 hours of ICU admission, we were not able to find any statistical association between early initiation of drugs and death. However, in a recent study published by Stabler et al. (34), adequate empiric antimicrobial therapy was associated with a better outcome. This result was also highlighted previously by Zahar et al. (18). Mortality rates for Clostridioides bacteremia reported in the literature were 15%-48% (17)(18)(19)(28)(29)(30)(31), which is lower than the mortality rates reported in our study. Indeed, Yang (31) and Fujita (17) revealed that patients who developed shock and required transfer to the ICU had worse outcomes than other patients. In those studies, shock was statistically associated with increased deaths. The prognosis for Clostridioides bacteremia patients is also related to underlying conditions that predispose to Clostridioides bacteremia and possibilities of therapeutic interventions in addition to prompt and appropriate antimicrobial drugs. As demonstrated by Rechner et al. (1), patients who required medical intervention to treat Clostridioides bacteremia had lower survival rates than patients who were managed by surgery. Conversely, the presence of massive intravascular hemolysis is a marker of extreme severity, despite appropriate management (16,40). Hemolysis is induced by Clostridioides toxin A (29), which hydrolyzes phospholipids in erythrocyte membranes, causing spherocytosis and subsequent intravascular hemolysis. Present in 17% of patients in our cohort, hemolysis is associated with a dramatic increase in mortality rate and remains a strong prognostic factor identified in our study. Finally, Clostridioides bacteremia in the ICU is associated with a higher mortality rate than that for classic septic shock in the ICU (41,42), which makes Clostridioides bacteremia a particularly difficult infection to deal with in the ICU.
The first limitation of our study is its retrospective nature and the inherently associated bias, such as missing data and unidentified confounding factors that may have been overlooked in the data collection. However, because of the rarity of Clostridioides bacteremia, prospective studies would hardly be feasible. Second, there are no standardized ICU admission policies for these patients, and patient recruitment patterns may have influenced the findings. Given the rapidity of the onset of symptoms and the severity Figure 3. Several examples of hematogenous spreads or myonecrosis related to Clostridioides bacteremia in patients in France. All these localizations were associated with air formation. A) Brain abscess (asterisk) associated with pneumocephalus (stars) and gas embolism in the superior sagittal sinus (arrow). B) Splenic abscess (asterisk) with gas formation. C) Hepatic abscess (arrow) with gas formation. D) Massive pelvic gangrene (asterisk) identified as the origin of the bacteremia in a patient. E) Cervical cellulitis (asterisks), identified as the origin of the bacteremia in a patient. of illness, rapid ICU management was the rule in the participating centers. However, we could not exclude that some patients, because of their advanced age or underlying conditions, were considered too sick for admission to the ICU and may have been denied intensive care.
In conclusion, Clostridioides bacteremia is an aggressive infection that often leads to failure of multiple organs, requiring prompt intensive care management. Particular attention should be paid to patients who have underlying conditions and are experiencing hemolysis. Early administration of antimicrobial agents active against Clostridioides bacteremia is essential, considering that most Clostridioides species are sensitive to β-lactams drugs. Even with prompt and appropriate management, however, Clostridioides bacteremia is associated with a high mortality rate in the ICU.

About the Author
Dr. Morel is a specialist in intensive care at the medical intensive care unit of Hautepierre Hospital-University Medical Center, Strasbourg, France. His primary expertise is in infectious diseases and immunocompromised patients.