Posted: July 13th, 2010 - 3:22pm

Abstract
The National Institute for Public Health Surveillance and the French National Reference Laboratory for Yersinia launched a postal survey among a sample of medical laboratories covering the French territory to: (i) define the proportion of stools samples in which the presence of Yersinia was looked for, (ii) evaluate the frequency of Yersinia isolation from stool cultures, (iii) make an inventory of the methods used for Yersinia isolation and identification, and (iv) determine the level of strain characterization.
Among 953 contacted laboratories, 483 (51%) completed the questionnaire. Most laboratories searched for Yersinia in stool cultures, but not in a systematic manner. In 2003, these laboratories performed 256,871 stool cultures and a search for Yersinia strains was carried out in only 53% of them. A Yersinia strain was isolated in 333 cases (isolation rate of 0.25%). The methods used for the recovery of Yersinia strains from stools were most often appropriate and relied on the isolation on CIN medium incubated at 28/30°C for 24 to 48 hours, occasionally preceded by an enrichment step. In most cases, the laboratories used appropriate isolation procedures. Genus and species identification were mainly performed with the API20E identification strip. However, without associated tests, this method does not allow a completely reliable species identification. Other characterization tests (biotyping, serotyping) were seldom performed, although they are necessary to differentiate pathogenic from non-pathogenic strains. Antibiotic susceptibility tests were most often performed, with appropriate procedures (Mueller-Hinton medium incubated at 37°C), and on antibiotics potentially usable for yersiniosis therapy.
Globally, this survey shows that the search for Yersinia in patients' stools was far from being systematic in medical laboratories in 2003 and that there was a striking disparity in isolation capacities among French laboratories. The number of Yersinia infections is likely to be largely underestimated, in the absence of tests differentiating pathogenic and non-pathogenic isolates, unnecessary treatments are probably prescribed to patients in whom a nonpathogenic Yersinia has been isolated.