Case–Control Study Of Clostridium Innocuum Infection, Taiwan Ⅱ
Jun 04, 2024
Results
Participants and Demographic Information
By the MALDI-TOF mass spectrometry system, 180 samples yielded the growth of C. innocuum. We excluded 22 of those from further analysis because of lack of access to clinical information and 6 because of concomitant isolation of C. inoculum and C. diffile from the same sample (CI group). We matched the control group with C. inoculum samples by the study criteria. From 1,134 C. difficile cases during the study period, we enrolled 304 cases as controls (CD group). All control cases were matched precisely on diagnostic year and age (+2 years); 25 controls were not matched on sex. The mean patient age for the 456 cases was 66.7 years, and 58.3% of patients were male (Table 1). Both groups were similar regarding age, sex, and Charlson Comorbidity Index score (5.7 + 3.2 for CI and 6.2 + 3.3 for CD). Subgroup analysis of each age group (<50, 50–60, 60–70, 70–80, and >80 years) also revealed no statistical difference. Overall, 8 pediatric patients were recruited, 3 in the CI group and 5 in the CD group. Regarding underlying systemic diseases, the CD group showed more patients with chronic kidney disease (18.4% vs. 30.9%; p = 0.005) (Table 1). Of note, more patients acquired the infection in the community in the CI group (33.6% vs. 16.8%; odds ratio [OR] 2.5, 95% CI 1.6–3.9; p<0.001) (Table 1).
Disease Characteristics and Severity
We observed notable differences in disease characteristics between the 2 groups. Those in the CI group had a 6.5 times higher risk of developing EICI, including bacteremia, intra-abdominal infection, biliary tract infection, skin and soft tissue infection, pyospermia, and bacterial vaginitis (36.8% for CI vs. 8.2% for CD; OR 6.5, 95% CI 3.9 –11.0; p<0.001) (Table 1). On the contrary, most disease manifestations in the CD group were confined to the intestine and colon, mainly C. difficile–associated diarrhea. Most patients had antibiotic exposure 30 days before the CI or CD infection event. CD group showed a higher 30-day antibiotic exposure rate (95.1%) than the CI group (79.6%; p<0.001) (Table 2) and longer duration (mean 15.6 days, SD 8.3) than the CI group (mean 13.7 days, SD 8.6; p<0.001). Patients in the CD group received more penicillins, cephalosporins, carbapenems, and fluoroquinolones (Table 2).
Regarding disease severity, most of the patients in both groups required hospitalization (93.4% in the CI group and 97.7% in the CD group; p = 0.03) (Table 1). Although most patients in the CD group had intestinal infections, gastrointestinal tract–related complications of ileus, bowel perforation, clinical sepsis, and shock occurred more frequently in the CI group (26.3%) than CD group (11.2%; OR 2.8, 95% CI 1.7–4.7; p<0.001). CI group also showed a higher rate of intensive care unit (ICU) admission (23.6% vs. 9.5%; OR 2.9, 95% CI 1.7–5.0; p<0.001) (Table 1). All the data indicated that the disease severity at the acute stage was more severe and invasive in the C. innocuum–infected patients. Furthermore, we saw no recurrence of infection in the CI group but a recurrence of infection in 4.9% of the CD group (p = 0.005).
We observed no statistically significant differences in clinical presentations, but patients with C. inoculum infection had fewer diarrheal symptoms and less fever. In the laboratory testing results, patients experienced anemia more commonly in the CD group than in the CI group; hemoglobin counts were 9.8 (2.0) g/dL in CD and 10.7 (2.4) g/dL in CI (p<0.001) (Table 3). We observed no difference in other systemic inflammatory markers. A limited number of patients received colonoscopy examination, and we found no pseudomembranous colitis in the CI group
Figure. Kaplan-Meier curve of 30-day (A), 90-day (B), and overall (C) survival rates of patients with Clostridioides difficile and Clostridium innocuum, Taiwan. In the C. inoculum group, the 30-day survival rate was 85.5%, the 90-day survival rate was 84.2%, and the overall survival rate was 77.0%. The 90-day survival rate was slightly higher than the C. difficile group (p-value of log-rank test = 0.05), whereas the 30-day and overall survival rates did not show a significant difference between the 2 groups.
Outcome and Risk Factors for Mortality Rate
The 30-day mortality rate in the CI group was 14.5%; the 90-day rate, was 15.8%, and the overall rate, was 23.0%. Although the 90-day mortality rate was slightly higher in the CD group with a significant difference (p-value of log-rank test = 0.05) in Kaplan-Meier survival analysis, the overall mortality rate did not show a statistically significant difference between the 2 groups (Figure). Using logistic regression, we identified chronic kidney disease (OR 8.6, 95% CI 2.6–28.4; p<0.001), solid tumor (OR 3.5, 95% CI 1.0–12.0; p = 0.051), ICU admission (OR 7.3, 95% CI 2.4–21.9; p<0.001), and shock status (odds ratio 8.0, 95% CI 2.4–27.2; p<0.001) as 4 independent risk factors for both 30-day and overall mortality rates in the patients with C. innocuous infection. We identified 7 bacteremias caused by C. innocuum in this study. Two of those patients experienced septic shock, and 1 needed ICU hospitalization. The 30-day mortality rate for the 7 patients was 42.9% (3/7) and the 90-day was 57.1% (4/7).
Microbiologic Result and Antimicrobial Susceptibility Among the 152 C. inoculum isolates, we recovered 96 (63.2%) isolates from stool specimens; the rest were from the blood (7), ascites (13), pus/abscess (16), wound/deep tissue (16), bile juice (2), endocervix (1), and semen (1). We detected 18 polymermicrobial infections in the CI group, most of which were from ascites and pus/abscess samples. More C. inoculum isolates (36.8%) than C. difficile isolates (8.2%) were from extraintestinal specimens (p<0.001) (Table 3), which is compatible with our clinical observation. We performed antimicrobial susceptibility testing on limited isolates. In the C. inoculum isolates, we observed the highest susceptibility rate for metronidazole (20/20, 100%) and ampicillin/sulbactam (21/21, 100%), followed by penicillin (35/44, 79.5%) and clindamycin 30/44 (68.2%).
Discussion
Genus Clostridium is large and heterogeneous; it includes <200 species. Accurate species identification has been difficult. In recent years, several new species have been recognized and others reclassified using newer molecular diagnostic methods, such as 16S rRNA gene sequencing (24). Among the medically important Clostridium spp., C. perfringens is the predominant species isolated from cases of bacteremia. The severity of EICI varies; for bacteremia, the mortality rate was found to be 48%–52% by different studies (25–27). The risk factors for disease acquisition and death were related to an underlying immunocompromised condition such as hemodialysis, malignancy, immunosuppressant use, and Crohn's disease (25). The main portal of entry is the hepatobiliary and gastrointestinal tract. We believe this is also the case in C. innocuum because stool was a common source for the C. innocuum isolates and gastrointestinal tract–related complications were not uncommon in C. innocuum–infected patients.
A recent study by Ha et al. (28) also found that C. inoculum is one of the most common bacteria that could translocate from the intestine to mesenteric tissue in patients with Crohn's disease and further induce adipogenesis and local fibrosis, known together as creeping fat. We found that among anaerobic clostridial species, C. inoculum has long been overlooked as a human pathogen. Our study is to date the most comprehensive observational study to depict the clinical manifestations and outcome of C. inoculum infection; not only it is more invasive than most Clostridium species, but it can cause more gastrointestinal tract complications following intestinal infection. Case reports of EICI related to C. inoculum infection have been published in the United States, Spain, Japan, and Taiwan (10,29–32) (Table 4). Bacteremia and intra-abdominal infection were the most common manifestations, which is compatible with our observations. All the infections occurred in patients with underlying conditions; prolonged antimicrobial therapy was required to treat these patients, whose mortality rate (20%) was similar to that observed in our study (23%). Compared to C. difficile, which is known to be a nosocomial pathogen, nearly one-third of the C. inoculum infections occurred in the community. This observation indicates that C. inoculum could be more virulent and competitive than C. difficile.
Among the EICI, bacteremia is the most severe form of infection. In a recent study by Morel et al. (33), non–C. difficile Clostridium bacteremia requiring ICU hospitalization showed an aggressive clinical course and was usually life-threatening. The 28-day mortality rate was 55% and the 90-day mortality rate was 71% (33). This report is compatible with our findings of 30-day (42.9%) and 90-day (57.1%) mortality rates in CI bacteremic patients. Identifying C. inoculum infection is important because the microorganism expresses intrinsic resistance to vancomycin, because of the synthesis of peptidoglycan precursors with low affinity for vanvancomycin (MIC 4–16 mg/L) (8,26). Moreover, highly vancomycin-resistant strains (MIC >16 mg/L) could develop if the bacteria were previously exposed to vancomycin (34). Because oral vancomycin has been recommended as the first-line therapy for C. difficile infection, distinguishing C. inoculum from other clostridial species becomes essential to avoid treatment failure caused by inappropriate antimicrobial use. Metronidazole and clindamycin appear to be appropriate choices for treating C. inoculum infection, according to our antimicrobial susceptibility testing results.
The main limitation of our study is the retrospective study design and the inevitable missing data. The lack of a standardized medical record format prevented us from precisely defining every case-patients diagnosis, especially antibiotic-associated diarrhea, and acute colitis, which have similar clinical descriptions in the medical records. Some objective data were not available, which may potentially compromise the accuracy of the estimated rates of presentations and diagnoses among the patients. However, the proportion of missing data appeared small and should not significantly affect the results of the study. Second, not all the C. inoculum isolates from the enrolled patients were tested for antimicrobial susceptibility, and that testing did not include vancoming. Third, the study does not advance our understanding of the virulence mechanism of C. invacuum. C. inoculum may possess a unique virulence mechanism to cause gastrointestinal as well as extraintestinal infections, such as the lipopolysaccharide-like structure we described in our previous study (9). C. difficile also contains surface lipo carbohydrate, which has a similar biologic activity to the lipopolysaccharide in gram-negative bacteria (35); this hypothesis needs further experimental verification. In conclusion, C. inoculum should be considered an important Clostridium species causing EICI and gastrointestinal infection that has a risk for severe complications and a high mortality rate in immunocompromised patients; physicians should recognize it as a pathogen to treat clinically. More studies are needed to understand the virulence mechanism of C. innocuum. Precise identification of C. inoculum will guide appropriate and timely antimicrobial therapy for patients because of its intrinsic vancomycin resistance.
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