Study: Most cases of CDI aren't being spread by patients in same ward

A recent study challenges the conventional assumption about how Clostridium difficile infection (CDI) spreads in hospitals, finding that almost three-quarters of the new cases aren’t transmitted by patients in the same ward.

CDI is a leading cause of hospital-acquired, antibiotic-associated diarrhea.  The study was published online in PLoS Medicine.

“At the start of this study, and in common with the wider clinical community, we had expected that the majority of CDI cases would be attributable to in-hospital transmission from other known symptomatic cases,” stated lead investigator A. Sarah Walker, PhD, from the National Institute for Health Research Oxford Biomedical Research Centre, John Radcliffe Hospital, Oxford, and the Medical Research Council Clinical Trials Unit, London, and colleagues.

Current infection-control policies and practices target in-hospital, known symptomatic cases, according to the researchers. The nearly 75% of unexplained transmissions raises concern about other routes not captured by the study, they noted. Therefore, these findings suggest that a better understanding of additional methods of transmission is needed to develop alternative interventions to control for infection and reduce the spread of the bacteria.

To investigate ward-based transmission of the bacteria, the researchers tested 29,299 stool samples from 14,858 patients with persistent diarrhea at Oxford Radcliffe Hospitals using both enzyme immunoassay and culture. Testing was conducted between September 1, 2007, and March 31, 2010. They then subdivided outbreaks using multi-locus sequencing typing and finally traced all contacts for up to 26 weeks to construct networks of cases and potential transmissions for each genotype.

In their findings, 1,282 (4.4%) of the samples tested positive for the bacteria in both enzyme immunoassay and culture, and they identified 69 different strains of C. difficile. However, only 23% of patients could be linked to another infected patient in the same ward. Most of the transmissions identified occurred less than 1 week after the onset of symptoms (141/218, 65%); some occurred more than 8 weeks following the onset of symptoms (21/218, 10%). Most incubation periods lasted a few days to 4 weeks (132/218, 61%), with some extending up to 12 weeks (28/218, 13%).

“[Ward-based transmissions] are the only cases currently visible to infection-control teams, and, therefore, are the only cases directly targeted by current infection-control policies and practice,” the authors said. “Improved tests, such as those based on nucleic acid/PCR-based methods, might improve detection rates, and it should be noted that even infections arising from an unknown source are to a certain extent preventable by measures such as good antimicrobial stewardship.”