Clostridium Marys

Clostridium difficile is an emergent bacterium. A close relative of the bacteria that cause tetanus and botulilsm (Clostridium tetani and Clostridium botulinum, respectively), C. difficile is an intestinal bacterium that can cause colitis. C. difficile has until recently been a fairly rare cause of disease, and then only typically within a hospital setting. However, the emergence of a new, highly virulent strain of the bacterium a few years ago, coinciding with an increase in the rate of serious infections it caused, put this pathogen on the map. And like methicillin-resistant Staphylococcus aureus, Clostridium difficile is no longer only found in hospitals: it's spreading among the community as well.

While this is a concern, the bulk of cases still occur in medical settings, where the bacterium is the most common cause of health care-associated diarrhea. Why is this such an issue in these settings? Like its cousins, C. difficile can form hard, resistant spores--making it difficult to eliminate when contamination occurs. Therefore, infection control measures have been able to reduce C. difficile contamination, but not completely eliminate it. A recen study looks at another reason for the difficulty in eliminating the organism from hospitals and other care facilities: undiagnosed healthy carriers shedding the bacterium.

Previous research had suggested that asymptomatic carriers didn't play much of a role in the transmission of the bacterium, but those were carried out prior to the emergence of the new strain, so researchers wanted to re-examine this hypothesis. The study examined 73 patients at a long-term care facility, looking for carriage of C. difficile (either the "epidemic" strain described above, or more run-of-the-mill isolates) as well as C. difficile-associated disease. To do this, they took samples from stool or rectum, and also swabbed skin and the environment (doorknobs, rails, etc.) They found a high rate of carriage in their sample population. In addition to 5 individuals who had C. difficile disease at enrollment, they found that:

Thirty-five (51%) of the 68 patients were asymptomatic carriers of toxigenic C. difficile strains...Twelve asymptomatic carriers had follow-up stool cultures performed 1-3 months after the initial culture survey, and 10 (83%) had persistent positive culture results.

They also examined risk factor for carriage, and found they were somewhat similar to those for developing C. difficile disease (with the addition that previous C. difficile disease itself was a risk for becoming a carrier of the bacterium--though you have a chicken-egg problem there, of course). In addition, carriers were more likely to have been exposed to any antibiotic in the prior 3 months, especially fluoroquinolones.

They then looked at their carriers to see which among them developed C. difficile disease. They found that, during their 6-month follow-up period, "16 (46%) of the asymptomatic carriers, including 5 of those with persistent positive culture results, were admitted to the acute care facility, and 7 (20%) of these patients developed C. difficile-associated disease (CDAD). Only 2 of the 7 asymptomatic carriers who developed CDAD had had a previous C. difficile infection."

The strains isolated from carriers were then examined, and it was found that 13 of the 35 carriers were colonized with the epidemic strain. The environment was also highly contaminated in both CDAD cases and asymptomatic carriers, with more than 20% of samples from bed rails, call buttons, phones, and tables yielding C. difficile. What's even more worrisome, though, is that over a third of the environmental samples were different than the ones carried in the patient's stool--meaning they could have come from other individuals. It's hard to say how long they could have been there as well--further emphasizing the difficulty of reducing transmission of this organism in a health care setting.

Finally, in this study only patients were tested--not the workers that care for them. How many of them are colonized? Are they spreading the bacteria? Is simple hand-washing enough to reduce transmission amongst carriers? These are issues infection control officers are already grappling with--now we just need the science to better inform them.

Reference

Riggs et al 2007. Asymptomatic Carriers Are a Potential Source for Transmission of Epidemic and Nonepidemic Clostridium difficile Strains among Long-Term Care Facility Residents. Clinical Infectious Diseases.