A dangerous hospital-related infection is now becoming common outside of them

Named from Greek kloster, for brooch, a class of bacteria called Clostridia abounds in nature.

Dark purple staining under a microscope, they come in the form of thin stems with a bulge at one end, resembling a seed of tadpole or maple. They thrive in the soil, marine sediments and humans. They live on our skin and in our intestines.

And sometimes they can kill you.

Most strains are harmless, but tetanus, botulism and gangrene are caused by Clostridium species. Vaccination, sanitation and improved medical care have made these infections less common, but a variety has been difficult to contain.

Clostridium difficile, or C. Diffcan cause life-threatening diarrhea and infection of the intestines. The virus was associated with nearly 30,000 deaths in 2011.

First considered a problem mainly limited to hospitals and nursing homes, research suggests C. diff rates in the community are on the rise and traditional risk factors may no longer tell the whole story.

C. diff was discovered in 1935 by scientists in Denver in the intestinal flora of healthy infants. The bacterium was safe for infants but proved deadly when it was injected into rabbits, providing an early indication of its danger.

At the same time, British scientists were at the forefront of the use of penicillin in the treatment of bacterial infections. The effectiveness of the drug was almost miraculous, but some patients developed severe diarrhea as a side effect. Since antibiotics became widely available in the 1950s, this side effect became more common.

Early researchers speculated that Staphylococcus aureus, a common pathogen, was the cause. The usual treatment for staphylococcus is the antibiotic vancomycin and many patients have improved. But the real cause was C. diff – it's a simple stroke of luck that vancomycin is effective against both.

In 1974, scientists in Cincinnati discovered a toxin in the stool of affected patients and determined C. diff.

A renewed interest for C. diff followed and the investigators quickly determined the risk factors for the disease. The use of antibiotics was already known, but hospitalization emerged as another dominant factor – to the extent that C. diff became almost exclusively an infection contracted at the hospital.

Clostridium species can become resistant spores that are resistant to disinfectants, resulting in many infections in hospitals and retirement homes. Health workers unknowingly spread spores and inoculated patients.

Scientists have also begun to wonder why antibiotics have triggered the infection. The answer seemed to be a simple ecology. In healthy intestines, the diversity of bacteria means that C. diff could not get a foothold for growth out of control. But once a series of antibiotics had flushed normal flora, C. diff could take over.

Improving infection control in hospitals has begun to reduce infection rates, but some studies have suggested that the problem may be more serious than everyone else thought.

In 1991, Australian scientists discovered that C. diff was responsible for 5.5% of ambulatory diarrheal infections, and researchers in Boston published additional evidence of C. diff in 1994. Subsequent work confirmed the existence of C. diff in the community, but suggested that the prevalence was low.

Things changed in 2006, when a hospital in North Carolina announced that 35% of C. diff infections occurred outside the hospital and only half could have been exposed to antibiotics. A survey conducted by the Centers for Disease Control and Prevention, using different methods, found that 20% of infections had no recent exposure to health care and only half had been exposed to antibiotics.

The work published in 2011 revealed that 40% of all C. diff infections in southern Minnesota were associated with the community. Even more worrying, investigators have seen a clear increase over time in the number of C. diff.

The CDC estimated that around 350,000 C. diff Infections occurred outside hospitals in 2011 and revealed that 46% of them had been acquired in the community and 36% had no exposure to antibiotics. Last year, California researchers found that 1 in 10 patients with diarrhea in emergency rooms had a positive test C. diffand that 40% had no risk factor.

Traditional risk factors – antibiotics and hospitalization – can no longer explain many infections. Scientists have long suspected that antibiotics trigger C. diff infections by disrupting the intestinal microbiome.

Could it be that other factors have a similar effect? Is our microbiome more and more sensitive to these dangerous infections?

Dr. Alice Guh, a researcher at the CDC, thinks so. "There is definitely something going on," she says, "but we do not really understand what."

The diet strongly influences the microbiome and could be an element, she says. A recent study has shown that trehalose, a common food additive, significantly improves the virulence of C. diffalthough Guh warns that it has been difficult to replicate the results.

Guh thinks that some common medications might also be involved. The popular medicines against heartburn that remove acid in the stomach are associated with C. diff infections, and have been shown to disrupt the microbiome.

And in March a study to Nature evaluated the effects of a thousand non-antibiotic drugs on friendly human colon bacteria and found that 25% had antimicrobial activity.

Rising rates C. diff infection in the community is a major public health concern. But could they be a sign of an even bigger problem, namely that our guts are becoming more and more fragile? Scientists have already discovered links between changes in the microbiome and a multitude of other human diseases.

Perhaps C. diff is just a canary in the mine.

Clayton Dalton is a resident physician at Massachusetts General Hospital in Boston.

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