dangerous strain of C. diff has been making people sick in 38 U.S.
C. diff sickens about a half million Americans every year, and every
year the epidemic gets about 10% bigger, CDC medical epidemiologist L. Clifford
McDonald, MD, tells WebMD.
Bigger -- and more deadly. The death rate is soaring by 35% a year.
From 1999 to 2004, the bug became four times more lethal, with death rates
increasing from 5.7 per million Americans to 23.7 per million Americans in
2004. During one hospital outbreak in Quebec, Canada, the one-year death rate
What's going on? WebMD has answers to these important questions:
- How bad is C. diff?
- Is C. diff a superbug?
- Why are C. diff cases rising so rapidly?
- Can you get C. diff from food?
- How do you get C. diff?
- Who is at risk?
- What are the symptoms?
- How is C. diff treated?
- How is C. diff prevented?
How bad is C. diff?
C. diff disease can range from mild diarrhea to life-threatening
colitis. The bug produces toxins that destroy the mucosal lining of the
There are many different C. diff strains circulating in the U.S. But
since 2000, one of these strains has gone from a minor player to become the
most frequently isolated C. diff strain. The strain has several names.
Referring to its genetic fingerprint, the CDC calls it NAP1. In Europe and
Canada, it's often called the 027 or BI strain.
The NAP1 strain of C. diff took off shortly after it acquired
resistance to fluoroquinolone antibiotics. There's some evidence it may also
have acquired some resistance to Flagyl, one of the two antimicrobial agents
used to treat it (the other is vancomycin).
Antibiotic resistance isn't the only worrisome thing about NAP1. C.
diff normally makes two toxins. The NAP1 strain makes 16 times more toxin A
and 23 times more toxin B. And it also makes another toxin, called binary
toxin, although it's not yet clear how this toxin affects humans.
To date, the NAP1 strain has been reported in 37 U.S. states and in the
District of Columbia.
A recent report shows that adult C. diff hospitalizations doubled
between 2000 and 2005 to about 300,000 hospitalizations a year. That's more
hospitalizations than are seen with MRSA, which sends about 126,000 Americans
to the hospital each year.
The CDC's C. diff expert, L. Clifford McDonald, MD, tells WebMD that
if you count pediatric C. diff cases and cases in the community that do
not enter the hospital, there are probably half a million U.S. cases of C.
diff infection each year.
And yes, it is an epidemic: The infection rate is going up by about 10% a
year. But the death rate is going up even faster, says Marya Zilberberg, MD,
adjunct professor at the University of Massachusetts, Amherst, and president of
the EviMed Research Group.
"The disease appears to be more likely to be fatal ¿ nearly doubling
from a 1.2% to a 2.2% case fatality rate," Zilberberg tells WebMD.
During a hospital outbreak in Canada, the one-year mortality rate for C.
diff infection was 17%.
"We're seeing increases both regionally and nationally in death
certificates listing C. diff infection," McDonald says. "And
hospitals are saying the same thing."
There are actually three ongoing C. diff epidemics. One is in
hospitals. Another is in the community. And a third is in livestock.
Is C. diff a superbug?
"Superbug" is not a scientific term. The CDC's McDonald prefers to
avoid it. The media originally coined the term to refer to germs that, like
Superman, became bulletproof: That is, they became impervious todrugs that
kill other germs. Dictionaries reserve the "superbug" designation for
germs resistant to drugs that used to kill them.
"Superbug" has also been used to describe germs that, like many
superheroes, once were normal but become super strong: That is, they became
much more virulent than they used to be.
"I think if I were to use the word "superbug" I might use it to
connote a particular strain or strains of a pathogen in which there has been a
convergence of increased resistance to antibiotics ¿ and increased
virulence," McDonald says.
All C. diff strains are resistant to many of the antibiotics normally
used to treat other infections. In fact, that's the problem. C. diff
most often strikes people whose intestinal flora have been disrupted by
antibiotic treatment. But most C. diff strains remain sensitive to
Flagyl and vancomycin, the drugs normally used to treat this infection.
The NAP1 strain of C. diff, however, is even more resistant to
fluoroquinolone antibiotics than other C. diff strains. It makes 20
times more toxin than normal strains. And most importantly, there's evidence it
causes more severe disease than other strains.
For these reasons, C. diff NAP1 is now being called a superbug,
although you won't see the term in scientific reports.
Why are C. diff cases rising so rapidly?
The number of hospital patients with C. diff infection went up and
down a bit from 1996 until 2000. But from 2000 to 2001 there was a steep
increase -- and that increase continued at least through 2006. Preliminary data
suggest the epidemic may have slowed a bit in 2007, but McDonald says it's too
soon to say it's leveled off.
What happened in 2000? McDonald says that's when the NAP1 strain -- which
has been around for at least 30 years -- developed fluoroquinolone resistance.
This resistance, plus what McDonald calls the strain's "hypertoxin
production," may explain why this strain has taken off.
Another reason for the epidemic is the rise of community-acquired C.
diff infection. C. diff usually is thought of as a hospital
infection, and community cases were thought to come from people who got C.
diff during a hospital stay but who didn't develop symptoms until they got
A 2006 study in Connecticut showed that community-acquired C. diff
disease struck seven people out of 100,000. One in four cases did not have the
risk factors normally associated with C. diff. Moreover, a third of
these cases had no exposure to antimicrobial drugs.
Where is the C. diff coming from? The vast majority of cases come
from person-to-person transmission (see below).
Can you get C. diff from food?
There's troubling evidence that at least a few cases come from food. There
are two reasons to think this might happen:
- In 2005, Canadian researchers bought 53 packages of beef and seven packages
of veal from five grocery stores in Ontario and in Quebec. One out of five
packages carried C. diff. Two-thirds of the C. diff isolates were
similar to the NAP1 strain.
C. diff isolates from human patients are quite similar to isolates
found in pigs and cattle. Some of the pig isolates are almost indistinguishable
from human isolates.
The CDC's McDonald says there is "at least the appearance" of
"migration" of strains epidemic in food-producing animals to humans.
That's because the animal epidemics occurred before the human epidemic.
"We think that direct transmission from animals to humans via the food
supply, IF it occurs at all -- no one has proven this -- would account for a
very small proportion of overall human C. diff infection," McDonald
writes in an email to WebMD.
The CDC, together with academic researchers, is culturing samples of retail
meats; result of these studies are expected soon. Eventually the CDC will look
at dietary risk factors associated with community-acquired C. diff
Even if you can get C. diff from food, the vast majority of
infections come from person-to-person transmission (see below).
How do you get C. diff?
Even many health care professionals wrongly think everyone carries C.
diff in their intestines and that the bug only overgrows when antibiotic
therapy or illness disrupts the normal gut ecology and gives it room to
That's not the case. Only 5% of the population is "colonized" by
C. diff. And because population studies have only looked at one point in
time, even most of these people may only be having a temporary infection.
Even so, more than half of Americans show evidence of a previous C.
diff infection some time in their lives. This often happens soon after
birth. But infants only rarely get C. diff disease. The reason for this
isn't clear, but there's evidence from animal models that C. diff toxins
have trouble binding to the immature gut.
C. diff bacteria are very sensitive to oxygen. But C. diff
spores are another matter. They are nearly indestructible and can survive for
months on dry surfaces. The CDC recommends disinfecting surfaces with bleach,
because the usual hospital disinfectants don't affect it.
People with C. diff infection have millions of C. diff spores
in their feces. These spores carry the infection to others via what experts
indelicately call fecal-oral contact. Careful hand washing rinses the spores
from contaminated hands, but alcohol gels won't do the trick.
Two things have to happen for you to get C. diff disease:
- You have to ingest C. diff spores.
- Something has to disturb the ecological balance of the normal bacteria
living in your colon.
Who is at risk?
More than nine out of 10 hospital infections with C. diff occur in
people who have received antibiotic treatment.
But community-acquired C. diff does not depend on antibiotics. The
CDC's McDonald says there's evidence that 30% to 40% of community-acquired
cases are in people not suffering a current or recent medical problem.
Fluoroquinolone antibiotics are most strongly linked to C. diff
disease. Risk is also higher for patients who receive multiple antibiotics and
for patients who receive longer courses of antibiotic treatment.
Other risk factors include:
- Age over 65
- Severe illness
- Nasogastric intubation
- Anti-ulcer medications. There is conflicting evidence on this.
- Long hospital stays, particularly in long-term-care facilities
It's not at all clear how long it takes to get C. diff disease after
you've ingested the spores. One study that performed a series of cultures in
hospital patients showed that patients who had C. diff disease were not
infected the week before.
This suggests incubation can occur in less than seven days. But another
study found an increased risk of C. diff disease throughout the first
four weeks after leaving the hospital.
What are the symptoms of C. diff disease?
Mild C. diff disease starts with mild to moderate diarrhea with no
blood in the stool. Sometimes there's cramping in the lower abdomen, too. Other
than mild abdominal tenderness, there aren't any other symptoms.
Severe C. diff disease is another matter. It starts with profuse
watery diarrhea and abdominal pain. Patients often have fever, nausea, and
dehydration. There may be a little blood in the stool, but very bloody stool is
These symptoms usually signal colitis, a serious bowel infection. If the
diarrhea stops afer severe colitis, it does not necessarily mean you're
getting better. It could be a sign of bowl paralysis and a life-threatening
condition called toxic megacolon. Most patients with toxic megacolon need
surgery -- and 32% to 50% of patients who undergo surgery for C. diff
Patients with symptoms of C. diff infection should seek immediate
medical attention. Mild C. diff disease can progress quickly to severe
Relapse is common after C. diff infection. There's an ongoing debate
over whether this is a true relapse or reinfection.
Whatever the cause, 12% to 24% of patients develop a second episode of C.
diff disease within two months. Patients who have two or more relapses have
a 50% to 65% chance of yet another recurrence.
How is C. diff treated?
Several different stool tests detect C. diff.
Before starting treatment, stopping treatment with whatever antibiotic
you've been taking could be enough. Before effective treatments were developed,
one study of 20 patients with C. diff colitis eventually recovered after
stopping their antibiotic treatment.
However, doctors will almost always treat C. diff infection with
antibiotics. Flagyl is the first-line treatment of choice for mild disease,
although patients must be followed closely to be sure this treatment works.
Vancomycin is an option for treatment for moderate or severe disease.
There is evidence that treatment with probiotics -- good bacteria that
repopulate the gut -- makes antibiotic treatment more effective and prevents
relapse. Saccharomyces boulardii appears to be particularly effective,
although good results have been seen with Lactobacillus species as
How is C. diff prevented?
C. diff is a preventable disease. There are two main means of
- Wash your hands. Frequent and careful hand washing keeps you from getting
C. diff spores on your hands and carrying them to your mouth.
- Use antibiotics only when absolutely necessary. Most respiratory infections
are caused by viruses, so don't demand antibiotics from your doctor every time
you get the sniffles or a cough.
By Daniel DeNoon
Reviewed by Louise Chang
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