In critically ill patients admitted to the ICU, diarrhea (defined as three or more watery loose stools within 24 hours) is a common problem. The etiologies of diarrhea are many, with infectious and noninfectious causes encountered.
Clostridium difficile infection (CDI) is the most common infectious cause of diarrhea in the hospital, including the ICU. The Centers for Disease Control and Prevention estimates the number of overall CDI cases to number about a half-million per year, of which 1 in 5 patients will have a recurrence, and 1 in 11 people aged ≥65 years will die within a month of CDI diagnosis. Age is a poor prognostic risk; greater than 80% of C difficile deaths occur in people 65 and older.
The increased use of electronic sepsis screening tools and aggressive antibiotic treatment, often done through protocols, has recently been identified as paradoxically increasing CDI occurrence (Hiensch R et al. Am J Infect Control. 2017;45:1091). However, similar rapid identification and management of CDI can result in improved patient outcomes.
Issues with diagnosing CDI
Episodes of CDI can be rapid and severe, especially if due to hyper-toxin producing–strains of C difficile, such as BI/NAP1/027, which produces significantly higher levels of Toxin A, Toxin B, and binary toxin CDT (Denève C, et al. Int J Antimicrob Agents. 2009;33:S24). Testing for CDI has been controversial; several methods have been employed to aid in the diagnosis of CDI. Currently, many institutions use either nucleic acid amplification tests (NAATs) for toxigenic C difficile or direct detection of the toxin produced by the bacteria. NAATs and past culture-based methods are more sensitive but less specific than toxin assays, whereas toxin assays are less sensitive but more specific than NAATs. However, detection of C difficile colonization due to high-sensitivity NAATs has caused a rise in the apparent rate of hospital-acquired CDI (Polage CR, et al. JAMA Intern Med. 2015;175:4114).
To counter this, multi-step algorithmic approaches to CDI diagnosis have been recommended, including the use of glutamate dehydrogenase (GDH) antigen, toxin detection, and NAATs for toxin-producing C difficile. These multistep pathways attempt to minimize false-positive test results while affirming the presence or absence of true CDI (Fang F, et al. J Clin Microbiol. 2017; 55:670).
However, controversy continues regarding which testing modalities are optimal, as some patients with positive toxin assays have asymptomatic colonization while some patients with negative toxin assays have CDI. The hope is that emerging, higher sensitivity toxin assays will decrease the number of CDI cases missed by negative toxin tests. Because C difficile toxins are labile at body temperature and susceptible to inactivation by digestive enzymes, stool samples must be expeditiously transported to the lab (time is of the essence), so as not to lose toxin or NAAT target detection. Repeat CDI testing for a “test for cure” is not recommended.
Management of CDI
The initial management of CDI has been discussed in many publications, including the current SHEA/IDSA Guidelines (Cohen SH, et al. Infect Control Hosp Epidemiol. 2010;31:431).
Briefly, this involves stratifying CDI patients by clinical severity (mild, moderate, severe) and objective data (leukocytosis >15,000, septic shock, serum creatinine level > 1.5 times premorbid level) to guide initial antibiotic therapy. For mild/moderate first episode of CDI, oral or IV metronidazole is generally recommended; more severe disease is generally treated with oral vancomycin.
Complicated CDI in patients (hypotension/shock, ileus, toxic megacolon) requires aggressive management with both IV metronidazole and oral vancomycin (if ileus is present, consider vancomycin enemas). Additionally, fidaxomicin is available for oral CDI treatment and has been associated with decreased first-episode CDI recurrence.
The management of CDI recurrence commonly involves using oral vancomycin as a taper (or taper/pulse regimen) or using fidaxomicin. A recent publication (Sirbu et al. Clin Infect Dis. 2017;65:1396) retrospectively compared vancomycin taper and pulse treatment strategies for 100 consecutive patients with CDI.
After taper, patents who received every other day (QOD) dosing had a cure rate of 61%, while those who received QOD dosing followed by every third day dosing achieved an 81% cure rate. A clinical trial comparing vancomycin standard therapy vs vancomycin taper with pulse vs fidaxomicin for first- and second-recurrence of CDI is underway.
Last year, the FDA approved bezlotoxumab, a monoclonal antibody that binds to C difficile toxin B. Bezlotoxumab treatment is indicated to reduce CDI recurrence in patients >18 years of age and is administered while CDI antibiotic therapy is ongoing.
When comparing 12-week efficacy using standard of care (SoC) CDI treatment vs SoC plus bezlotoxumab (SoC+Bmab), recurrence rates in SoC and SoC+Bmab were 27.6% vs1 7.4%, respectively, in one trial, and 25.7% vs 15.7% in another. While generally well-tolerated, bezlotoxumab is associated with increased risk for exacerbating heart failure. Data relating to the cost-effectiveness of bezlotoxumab are currently pending.
Fecal microbiota transplant (FMT)— duodenal or colonic instillation of donor fecal microbiota to “restore” normal flora— is an evolving CDI therapy with promising results but difficult administration. Although FMT has high published success rates, the FDA’s policy of “enforcement discretion” permits practitioners to proceed with FMT only as an Investigational New Drug. This requires signed, informed consent to FMT as an investigational therapy with unknown long-term risks.
The FDA deemed these protections necessary as ongoing studies of the human microbiome have yet to define what constitutes “normal flora,” and some investigators highlight the possibility of transmitting flora or gut factors associated with obesity, metabolic syndrome, or malignancy.
Experimental CDI preventive modalities include new antibiotics, monoclonal antibodies, probiotics, select other novel agents, and C. difficile vaccinations. These vaccines include recombinant fusion proteins and adjuvant toxoids, both of which have generally favorable tolerance profiles, as well as robust immune responses in clinical trial subjects. However, the efficacy of these vaccines at preventing clinical disease is still to be demonstrated.
Lastly, the ubiquitous use of proton pump inhibitors (PPI) in ICUs plays a role in promoting CDI incidence, severity, and recurrence. Accordingly, the pros and cons of PPI use must be weighed in each patient.
CDI prevention in the hospital environment
Hospital-acquired CDIs (HA-CDI) and nosocomial transmission clearly occur. A recent study of electronic health record data demonstrated that patients who passed through the hospital’s emergency department CT scanner within 24 hours after a patient with C difficile were twice as likely to become infected (Murray SG, et al. JAMA Internal Medicine. published online October 23, 2017. doi:10.1001). Receipt of antibiotics by prior bed occupants was associated with increased risk for CDI in subsequent patients, implying that antibiotics can directly affect the risk for CDI in patients who do not themselves receive antibiotics. As such, aggressive environmental cleaning in conjunction with hospital antimicrobial stewardship efforts, such as appropriate use of antibiotics known to increase CDI occurrence, are required to minimize HA-CDI.
Contact precautions should be strictly enforced; wearing gloves and gowns is necessary for every encounter when treating patients with C difficile, even during short visits. Hand sanitizer does not kill C difficile, and although soap-and-water hand washing works better, it may be insufficient alone, reinforcing the importance of using gloves with all patient encounters.
The strain placed on ICUs by CDI has been increasing over the past several years. Physicians and hospitals are at risk for lower performance scores and reduced reimbursement due to CDI relapses. As such, burgeoning areas of debate and research include efforts to quickly and accurately diagnose CDI along with reducing recurrence rates. Yet, with all the capital investment, the most significant and cost-effective method to reduce CDI rates remains proper and frequent hand washing with soap and water. Prevention of disease remains the cornerstone to treatment.