Changes in Testing
For example, new data published in The New England Journal of Medicine underscore the shortcomings of advances in testing technology, suggested Sahil Khanna, MBBS, an associate professor of medicine at Mayo Clinic College of Medicine and Science, in Rochester, Minn. (2020;382:1320-1330).
At first glance, the study, which used data from 10 sites nationwide to derive a national estimate of the incidence of CDI, reported a relatively unchanged rate of the disease over a six-year period: 476,400 cases in 2011 and 462,100 cases in 2017. However, Dr. Khanna noted that after adjusting for the increasing use of nucleic acid amplification testing (NAAT), the researchers concluded that the incidence of CDI had actually decreased by 24% during the study period, including a 36% drop in healthcare-acquired CDI cases.
The study highlights a problem with NAAT, according to Khanna.
“NAAT is approximately 95% sensitive in detecting the C. difficile gene, but it cannot determine if the gene is active and toxin-producing, so it has the potential for overdiagnosis and for producing clinical false positives,” he explained. “Because of this, it’s important that we interpret NAAT results in the context of patient symptoms.”
Clinicians must be selective when deciding which patients should be tested, he said, only using it in patients who have acute diarrhea with no obvious alternative explanation, and who have the risk factors for CDI. These include older age, longer hospitalization, immunosuppression, use of antibiotics, gastric acid-suppressing agents, gastrointestinal surgery, manipulation of the gastrointestinal tract, and tube feeding.
“Patients not experiencing an active infection can be colonized with C. difficile, in which case there is a risk of a clinical false positives and unnecessary treatment,” Khanna emphasized.
An alternative testing approach now recommended by the Infectious Diseases Society of America (IDSA) and the Society for Healthcare Epidemiology of America (SHEA) is the use of a multistep algorithm including glutamate dehydrogenase (GDH) to identify pathogenic bacteria and enzyme immunoassay (EIA) to detect C. difficile toxin (Clin Infect Dis 2018;66:e1-e48). NAAT should be reserved for instances in which results from GDH and EIA are inconclusive, the guidelines recommend.
“Unfortunately, NAAT remains the most commonly used test method,” Khanna said, adding that laboratories are increasingly adopting a two-step protocol of GDH and EIA.
Recurrent CDI mostly occurs in people:65 and older who take antibiotics and receive medical care
staying in hospitals and nursing homes for a long time with weakened immune systems
The treatment landscape for CDI also has changed over the past few years, noted Kim Ly, PharmD, a clinical pharmacy specialist in critical care and infectious diseases at Sunrise Hospital and Medical Center, in Las Vegas. Bezlotoxumab (Zinplava, Merck), a monoclonal antibody, is now approved for combination treatment of toxin B–producing CDI, along with an established antibiotic. Additionally, metronidazole, while still approved for the treatment of CDI, is no longer recommended by IDSA/SHEA as a first-line agent for primary CDI in adults.
“For severe initial episodes of CDI, oral vancomycin and fidaxomicin [Dificid, Merck] are now the preferred agents, and metronidazole is only recommended for nonsevere initial episodes when patients are unable to be treated with oral vancomycin or fidaxomicin,” Kim explained.
For a first recurrence of CDI, the IDSA/SHEA guidelines recommend administering oral vancomycin as a tapered and pulsed regimen or fidaxomicin, rather than a standard 10-day course of vancomycin. For subsequent recurrences, clinicians can use the same regimen, with the addition of a standard course of oral vancomycin followed by rifaximin or fecal microbiota transplantation (FMT).
Metronidazole comes into play again in the management of fulminant CDI, Ly noted.
“The IDSA/SHEA guidelines recommend treating this with oral or rectal vancomycin 500 mg four times daily along with intravenous metronidazole,” she explained.
Given that antibiotic-induced microbiota disruption “is far and away the number one precipitant for getting recurrent CDI,” selecting the CDI treatment with the least impact on the microbiota is important, said former IDSA president Cynthia Sears, MD, a professor in the Department of Medicine, Division of Infectious Diseases, at the Johns Hopkins University School of Medicine, in Baltimore.
“Vancomycin is the most commonly used therapy for CDI and its recurrences, but it decreases intestinal diversity and so impedes the recovery of the normal microbiota after CDI, setting the stage for CDI recurrence,” Sears said. “We have learned that vancomycin hits the colon with full force when taken orally because it is not absorbed, and it has off-target effects on lots of anaerobic bacteria that are essential to intestinal resistance of CDI.”
Fidaxomicin has less of an effect on the microbiota and has been shown to sometimes decrease the risk for CDI recurrence when compared with vancomycin (N Engl J Med 2011;364:422-431), but it can be expensive, she said.
Fecal Microbiota Transplantation
FMT is a less expensive, highly effective treatment that has received increasingly widespread attention, specifically for the management of recurrent CDI. Despite the enthusiasm surrounding the treatment, Sears expressed significant reservations about employing it.
“While there’s no question that FMT benefits patients with recurrent CDI, I feel we don’t yet have a quality-controlled product that we know is safe as well as being effective,” she said.
Sears pointed to two recent FDA safety alerts that warned of the harm that FMT can cause. The first, from 2019, reported that stool from a single donor had not been thoroughly screened before FMT and contained extended-spectrum ss-lactamase–producing Escherichia coli. The specimen had been used in separate FMTs for two immunocompromised patients, leading to infection with the pathogen and death in one case.
In another FDA safety alert from earlier this year, the organization said a stool bank specimen that had undergone comprehensive screening nevertheless contained enteropathogenic E. coli and Shiga toxin-producing E. coli. Transfer of the stool for the treatment of recurrent CDI resulted in one nonfatal infection and one death.
“Stool banks try very hard to be sure their specimens are free of disease-causing microbes, but if you have very low-level colonization, molecular diagnostics can miss this,” Sears said. More recently, she noted, the FDA has also raised concerns about the possibility of transferring SARS-CoV-2 through FMT, given that the virus can be present in the stool of infected individuals.
What would a safer and equally effective microbiota-based treatment look like? According to Sears, while microbial diversity seems to be protective against recurrent CDI, there are suggestions that the administration of specific strains may be able to treat CDI and can be produced under the same strict quality control manufacturing processes as other FDA-approved drugs. One study published in 2015 using human and mouse samples found that colonization with Clostridium scindens, a strain of Firmicutes, increased resistance to CDI (Nature 2015;517:205-208). Many microbiota-based therapeutics are in the research pipeline as well.
“I am optimistic that we will see something emerge that’s safer and still as effective as FMT for patients, whether it’s an orally or rectally administered product,” Sears said.