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Though the findings are very preliminary, there is some evidence to suggest that Clostridium difficile may be arising independently as a community pathogen a la methicillin-resistant Staphylococcus aureus.

C. diff takes on troubling new guise in community

C. diff takes on troubling new guise in community

Cases in absence of antibiotics unheard of’

Though the findings are very preliminary, there is some evidence to suggest that Clostridium difficile may be arising independently as a community pathogen a la methicillin-resistant Staphylococcus aureus.

"I think that is very possible," says L. Clifford McDonald, MD, medical epidemiologist in the division of health care quality promotion at the Centers for Disease Control and Prevention. "A lot of people always think this is stuff leaking out of the hospital. That is actually not what happened with MRSA. They were actually two parallel events and that may be what is happening here."

Particularly disturbing are new reports in four states of infections in patients previously thought to be at low risk for C. diff. Considered in the context of recent high-morbidity, hospital-associated outbreaks in North America, Great Britain, and the Netherlands, the cases of severe C. diff appear to reflect a "changing epidemiology," the Centers for Disease Control and Prevention reports.1

Clinical features that have been less common in the past include close-contact transmission, high recurrence rate, young patient age, bloody diarrhea, and lack of antimicrobial exposure. In Pennsylvania and three other states, severe C. diff infections have occurred in two groups traditionally considered at low risk: healthy people living in the community and peripartum women (those in the last month of gestation or the first few months after delivery), the CDC reported.

The cases rose sufficient concern that the CDC decided to publish the data it had even as the investigation continued, McDonald says. "It was alarming what proportion of them had to go into the hospital, what proportion were seen in the ER and what proportion had recurrence," he says. "Seven of the 23 community associated cases did not have [prior exposure to] antibiotics."

An alarming development

Onset of C. diff in the absence of antibiotic exposure is "virtually unheard of," says C. diff researcher Dale Gerding, MD, associate chief of staff for research at the Hines VA Hospital and professor of medicine at Loyola University of Chicago. "You can’t get this disease — as best we can tell — unless you have some disruption of your normal bacteria. Your normal bacteria are protective and keep it out. If you take antibiotics then you are susceptible and the organism is in the community. There have always been community cases so it isn’t as though this is something new. It’s just that the risk is much lower in the community then it is in the hospital setting."

In addition to less antibiotic pressure, the risk is lower in the community because environmental contamination is not the issue it is within hospitals. But four of the community onset cases had contact with a close family member or friend with suspected C. diff, McDonald adds.

"There is this issue of family clusters of transmission, which is also very unusual," he says. "You usually think about C. diff in the hospitalized older person with antibiotics. You tell the family it is not likely to transmit to you unless you are on antibiotics. That is still a true statement. I don’t think this turns everything on its head yet, but it does make us start to at least think about the fact that C. diff may be changing in some way — [becoming] more like other kinds of diarrhea that you can get without antibiotic [exposure]."

Still, it’s too early to attach much public health significance to the report given the limitations of the data, Gerding adds. "It’s pretty anecdotal right now," he says. "They were just voluntarily reported cases. It is not clear that there is really an unusual or high rate of disease. If it is more frequent, is this due to a new strain that is circulating in the community? They only had two isolates and neither of those were of the [new virulent] strain that is circulating in hospitals."

While not an exact match with the strain that is causing major problems in hospitals, the two community isolates did have a possibly significant genetic mutation, McDonald adds. "It is interesting that the two strains that we did get both shared some characteristics of the epidemic [hospital] strain," he says. "They both had an extra toxin known as binary toxin, which seems to be a new arrival in the C. diff organism."

That raises the question of whether C. diff is evolving in the community independently of hospital strains in much the same way as MRSA did. "We have to realize that these bacteria are frequently exchanged between people, the environment, maybe other animal hosts, and meanwhile they are also exchanging genetic information all of the time," McDonald says. "So we don’t know. Maybe there is a new gene cassette that has come into C. diff and has gone into several different strains. There has been an exchange of genetic information and certain factors that we don’t even know yet have occurred underneath the radar screen. Some of that is what is going on with MRSA."

Reference

  1. Centers for Disease Control and Prevention. Severe Clostridium difficile-associated disease in populations previously at low risk — Four states, 2005. MMWR 2005; 54(47); 1,201-1,205.