Effect of excluding duplicate isolates of Escherichia coli and Staphylococcus aureus in a 14 year consecutive database
2007 (English)In: Journal of Antimicrobial Chemotherapy, ISSN 0305-7453, E-ISSN 1460-2091, Vol. 59, no 5, 913-918 p.Article in journal (Refereed) Published
OBJECTIVES: It is recommended that duplicate isolates are excluded when reporting resistance rates. The rationale for this is that failing to do so will yield falsely high resistance rates. We analysed a 14 year consecutive database of Escherichia coli (n=62,380) and Staphylococcus aureus (n=28,178) using various cut-off algorithms to determine the importance of excluding duplicates and principal differences between the bacteria. METHODS: Susceptibility testing was performed according to the Swedish Reference Group for Antibiotics guidelines. Duplicates were excluded on the basis of species, individual and time (exclusion cut-offs of 7, 14, 30, 45, 90, 180, 270 and 365 days) from the first isolate. RESULTS: Although 30% of the isolates were excluded using a 365 day exclusion algorithm, the effects on resistance rates of excluding duplicates were small. Irrespective of cut-off, resistance in S. aureus decreased when duplicates were excluded. Using 7-30 days cut-offs, resistance in E. coli decreased or was not affected, whereas higher resistance rates were obtained when exclusion was based on a 365 day cut-off. Fluoroquinolone resistance was a clear exception to this rule. CONCLUSIONS: Although the effect of exclusion of duplicates was minor, we suggest that exclusion cut-offs should match the study timeline. The data presented on E. coli, from urinary tract infections, and S. aureus, from skin and soft tissue infections, suggest that E. coli infection, >90 days after the first culture, is mainly caused by new less-resistant strains. Patients with S. aureus continue to be colonized with the same strain.
Place, publisher, year, edition, pages
2007. Vol. 59, no 5, 913-918 p.
antimicrobial resistance, surveillance, urinary tract infections, skin and soft tissue infections
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:uu:diva-112600DOI: 10.1093/jac/dkm040ISI: 000247006200015PubMedID: 17332004OAI: oai:DiVA.org:uu-112600DiVA: diva2:286930