Evolution of a Superbug
According to Becky A. Miller, MD, who presented study results at an oral session at the Fifth Decennial International Conference on Healthcare-Associated Infections 2010, hospital-onset, healthcare-associated Clostridium difficile infections (CDI) have increased in frequency. Now, C. difficile has passed methicillin-resistant Staphylococcus aureus (MRSA) infections in the race to be the most prevalent healthcare-acquired infection (HAI) in hospitals.
Since 2007, MRSA infection rates have steadily decreased, whereas rates of CDI have increased. The Duke University study noted the rate of nosocomial CDI as 0.28 cases per 1,000 patient days and the rate of nosocomial MRSA was 0.23 cases per 1,000 patient days. This means nosocomial CDI occurred 25 percent more frequently than nosocomial MRSA.
Since C. difficile spores are shed in stool, these spores can live in the environment for months. The infections are not being prevented by the same methods that are working for MRSA, and the fear is that the above study may only point to the tip of the iceberg since the surveillance did not include CDI cases occurring after discharge.
Changing the Picture
Compounding C. difficile issues in hospitals is the fact that new variants and strains of CDI have increased in virulence, decreased in their response to metronidazole therapy. This is not only happening in hospital settings, but in the community where cases are showing up in nonelderly populations. Even more significant, a number of these cases occurred in patients with no recent hospitalization or antibiotic use, according to a study based on the Rochester Epidemiological Project, released in a presentation for the American College of Gastroenterology 2009 annual scientific meeting. Probable causes for this change may include an older population, broader use of antibiotics and a new, more virulent strain of CDI, according to Darrell S. Pardi at the Mayo Clinic in Rochester, Minn., senior author on the study.
Some cases are proving more difficult to treat with the resistant strains that are emerging and where they’re coming from is not always clear-cut, as it could be overuse of antibiotics or under treatment, where patients aren’t taking their full course of antibiotics or even a novel change of the bacteria that is occurring.
Another study presented at the Decennial described the Mayo Clinic’s targeted strategy to eliminate C. difficile using ultra-germicidal bleach wipes. Before the intervention, the incidence of CDI was 18.4 per 10,000 patient days. After the intervention the incidence decreased to3.76 per 10,000 patient days.
Carlene A. Muto MD, medical director for infection control at the University of Pittsburgh School of Medicine, noted that there is a large undetected reservoir in patients who asymptomatically carry CDI. Many studies have cited non-compliance with patient room cleaning but one key to controlling CDI may lie in the practice of cleaning all surfaces this way rather than only the ones in rooms of patients known to be infected.
Compounding this difficult picture is the fact that common hand-hygiene products are often ineffective at killing CDI as the bacteria is sticky, similar to anthrax. The C.difficile spores have an exosporium that confers a particulate adherence-sticky chains of protein containing substances that stick on hands says Dale Gerding, MD, associate chief of staff, research and development coordinator for Edward Hines Jr. VA Hospital. These results reinforce the need for contact precautions, complete with gloves, for the care of these patients.