September 25, 2013
Larry M. Baddour, MD reviewing Eyre DW et al. N Engl J Med 2013 Sep 26.
In a longitudinal study conducted in the U.K., CDI was often acquired from sources other than symptomatic patients.
Most cases of Clostridium difficile infection (CDI) are believed to result from healthcare exposure — particularly exposure to symptomatic patients with CDI. But is this belief correct?
To better define the epidemiology of CDI, researchers in the U.K. conducted a longitudinal study at four hospitals. From September 2007 through March 2011, all inpatients with diarrhea (defined as ≥3 stools within a 24-hour period that took the shape of a container) underwent testing for CDI. Enzyme immunoassay was used to screen all stool samples, and those that tested positive were cultured; culture-positive isolates were subjected to whole-genome sequencing. Sequences for samples obtained from April 2008 through March 2011 were compared with those for samples obtained from September 2007 onward, with genetic relationship defined as ≤2 single-nucleotide variants (SNVs) between samples.
Among single isolates from 1250 confirmed CDI, 1223 (98%) were successfully sequenced. The median age of patients with CDI was 78 years. Of the 333 patients whose isolates were genetically related to at least one previously obtained isolate, 126 (38%) had nosocomial exposure to the earlier patient. In contrast, 120 patients (36%) had no hospital or community contact with such a patient. Forty-five percent of strains isolated differed from all previous isolates by >10 SNVs and were deemed genetically distinct.
Even though enzyme immunoassay — an insensitive screening tool — was used in this investigation, the findings are important: Patients with symptomatic C. difficile infection are not the only source of transmission. Because whole-genome sequencing provides almost real-time results, it will likely be used with increasing frequency in epidemiologic investigations and infection-prevention efforts.
Eyre DW et al. Diverse sources of C. difficile infection identified on whole-genome sequencing. N Engl J Med 2013 Sep 26; 369:1195. (http://dx.doi.org/10.1056/NEJMoa1216064)