under the microscope
By Rodney E. Rohde, PhD, MS, SM(ASCP)CM SVCM, MBCM, FACSc
Exactly What is Clostridioides difficile (C. diff)?
C
lostridioides difficile (C. diff) is a bacterium that can cause
symptoms ranging from diarrhea to life-threatening
inflammation of the colon. It is a spore forming, Gram-positive
anaerobic (does not prefer oxygen rich environments) bacillus
that produces two exotoxins: toxin A and toxin B. Illness from
C. diff. commonly affects the elderly in hospitals or long-term
care facilities and typically occurs after use of antibiotics.
However, studies show increasing rates of C. diff. infection
among people traditionally not considered to be at high risk,
such as young and healthy individuals who haven’t used
antibiotics or been in a healthcare facility. Generally, C. diff.
considered a healthcare-associated infection (HAI).
Annually in the U.S., about a half million people get
sick from C. diff., and in recent years, these infections have
become more frequent, severe and difficult to treat. Recurrent
C. diff. infections also are on the rise. It is a common cause of
antibiotic-associated diarrhea (AAD). It accounts for 15 percent
to 25 percent of all episodes of AAD. The range of diseases
caused by this bacterium is known as C. diff. Infection (CDI).
In my personal experience of discussing HAIs, antibiotic-re-
sistant pathogens, and other microbes that are transmitted in
the healthcare or community setting, I try to put myself in the
place of an individual who has little understanding of these
pathogens. Effective science communication, and ultimately
raising the health literacy of the public, is everyone’s job in
healthcare. Here, I will offer C. diff. information aimed at a
general understanding of the characteristics of this pathogen
in the environment. Primarily, I will utilize information obtained
from the CDC, along with professional experience.
Which patients are at increased risk for CDI? The risk
for disease increases in patients with:
exposure (e.g., fluoroquinolones, third/fourth generation
cephalosporins, clindamycin, carbapenems)
gastrointestinal surgery/manipulation
long length of stay in healthcare settings
a serious underlying illness
immunocompromising conditions
advanced age
other possible causes include Proton pump inhibitors,
H2-blockers
Where is C. diff. found and what are the causes of CDI?
C. diff. bacteria are ubiquitous in the environment — in
soil, air, water, human and animal feces, and food products,
such as processed meats. A small number of healthy people
naturally carry the bacteria (colonized) in their large intestines
and do not have ill effects from the infection.
Spores from C. diff. are passed in feces and spread all over
the environment (food, surfaces and objects) when people
who are infected do not wash their hands thoroughly. Spores
are primarily a way for bacteria to survive in harsh times or
conditions. They persist for weeks or months. If you touch
a surface contaminated with C. diff. spores, you may not
10
realize you’ve swallowed the spore which can then become
a viable bacteria.
Once established, C. difficile can produce toxins that attack
the lining of the intestine. The toxins destroy cells, produce
patches (plaques) of inflammatory cells and decaying cellular
debris inside the colon, and cause watery diarrhea.
What are the differences between colonization and
infection?
Colonization is more common than CDI. The patient exhibits
no clinical symptoms (asymptomatic) but does test positive for
the C. diff. organism or its toxin. With infection, the patient
exhibits clinical symptoms and tests positive for the C. diff.
organism or its toxin. The difference is critical with respect
to understanding when an individual should be considered
positive for CDI (confirmatory medical laboratory test AND
clinical symptoms).
Which laboratory tests are commonly used
for diagnosis?
Most people are not experts in the world (or language) of
medical laboratory tests. The following is a list of common
tests that are often utilized in a medical or public health
laboratory to identify C. diff. and many pathogens. If you do
not understand a test, ALWAYS ask for clarification. This will
increase your health literacy.
Molecular tests: FDA-approved PCR assays, which test for
the gene encoding toxin B, are same-day tests that are highly
sensitive and specific for presence toxin-producing C. diff.
Antigen detection for C. diff: Rapid tests (<1 hour) that
detect the presence of C. diff. antigen. Nonspecific and
often used in combination with other tests.
Toxin testing for C. diff:
¢
Tissue culture cytotoxicity assay detects toxin B only.
¢
Enzyme immunoassay detects toxin A, toxin B, or
both A and B. Due to concerns over toxin A-negative,
B-positive strains causing disease, most laboratories
employ a toxin B-only or A and B assay.
¢ C. diff. toxin is unstable. The toxin degrades at room
temperature and might be undetectable within two
hours after collection of a stool specimen. False-negative
results occur when specimens are not promptly tested
or kept refrigerated.
Stool culture for C. diff: Most sensitive test available, but it is
often associated with false-positive results due to the presence
of nontoxigenic C. diff. strains.
Rodney E. Rohde, PhD, MS, SM(ASCP)CM SVCM, MBCM,
FACSc, serves as chair and professor of the Clinical Laboratory
Science Program at Texas State; associate director for the
Translational Health Research Initiative; as well as associate
dean for research in the College of Health Professions. Follow
him on Twitter @RodneyRohde / @TXST_CLS, or on his website:
http://rodneyerohde.wp.txstate.edu/
april 2020 • www.healthcarehygienemagazine.com