Published Date: 2004-10-04 23:50:00
Subject: PRO/EDR> Clostridium difficile, increased virulence - USA
Archive Number: 20041004.2735
CLOSTRIDIUM DIFFICILE, INCREASED VIRULENCE - USA
A ProMED-mail post
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International Society for Infectious Diseases
Date: Sun 3 Oct 2004
From: ProMED-mail <firstname.lastname@example.org>
Source: Canada.com [edited]
Researchers report emergence of epidemic strain of C. difficile
A strain of _Clostridium difficile_, with properties linked to increased
virulence, has become predominant in several American hospitals, prompting
researchers to suggest that the bacterial strain may be responsible for the
sharp increase in cases and severity of disease in parts of the USA.
It may also explain the exploding problem some hospitals in Canada are
experiencing with _C. difficile_, said lead author Dr Clifford McDonald of
the Centers for Disease Control and Prevention (CDC). "We have concerns
that Quebec may be dealing with the same strain," McDonald, a medical
epidemiologist who specializes in hospital acquired infections, said in an
It is too soon to say whether the strain afflicting Quebec hospitals is the
one the team has documented. "We do know that in Montreal, and in
Sherbrooke, there is predominantly a single strain. We don't know that it's
this strain," said Dr Allison McGeer, head of infection control at
Toronto's Mount Sinai Hospital.
McDonald agreed, noting CDC laboratories are testing isolates -- bacterial
samples -- from Quebec hospitals plagued by the problem to determine
whether they match what he and his co-authors are calling an "epidemic
strain." McDonald presented the findings over the weekend at the annual
meeting of the Infectious Disease Society of America in Boston. _C.
difficile_ has been blamed for nearly 100 deaths in Canada since 2001, with
the vast majority of the cases in Quebec hospitals.
McDonald's team looked at 169 isolates collected from 7 hospitals in 6
states that experienced _C. difficile_ outbreaks between 2001 and 2004.
They compared them to a database of more than 6000 isolates from prior to
2001. Senior author Dr Dale Gerding, an expert in _C. difficile_ based at
Loyola University in Chicago, compiled and maintains the database.
Historically, one would have seen a wide variety of strains of the bacteria
in isolates from each hospital, but the team found that a single strain
made up 50 per cent or more of the samples from 5 of the 7 hospitals, and
43 per cent in the 6th. In a New Jersey outbreak in June 2003, the strain
represented 75 per cent of the isolates. The strain is not new. Variations
of it were found in Gerding's database. But it appears to have acquired
additional resistance to antimicrobials, which may be allowing it to flourish.
Testing of the strain showed that it was fully resistant to antimicrobials
called fluoroquinolones, a class of broad-spectrum antibiotics suspected of
contributing to the rise of _C. difficile_ cases. Isolates of this strain
from before 2001 were not resistant to fluoroquinolones.
Some antimicrobial agents trigger _C. difficile_ disease by disrupting the
normal bacterial balance in the colon. If _C. difficile_ spores are
present, they can proliferate and take over, producing symptoms ranging
from persistent diarrhea to inflammation of the colon and, in severe cases,
The researchers found the epidemic strain contained an additional toxin,
which is believed to be a marker of increased virulence. The toxin was
previously rare: earlier studies found it in only 5 to 6 per cent of
isolates. The epidemic strain was also missing a gene that regulates
production of the A and B toxins normally made by the bacterium. The
researchers believe the deletion could result in increased toxin
production. The combination of factors may explain why disease severity has
increased sharply in the past few years.
"Here we've not proven ... increased virulence, but it's suggestive of it,"
McDonald said. The findings help to explain frequent anecdotal reports from
the health care front line of increasing _C. difficile_ case rates and
disease severity. But simply knowing what's going on won't solve the
problem, McDonald said. Better surveillance and infection control measures
are needed to contain _C. difficile_, otherwise, this strain will continue
its geographic spread, he warned.
[byline: Helen Branswell]
[Many of my colleagues and I have observed, albeit anecdotally, both an
increased severity of pseudomembranous enterocolitis due to _C. difficile_
and poorer responses to metronidazole therapy. The strain described above
could account for these observations. - Mod.LL]