Matching criteria in case-control studies in the field of antimicrobial resistance

Abstract number: 1733_1312

Falagas M.E., Mourtzoukou E.G., Giannopoulou K., Alexiou V.G., Rafailidis P.I.

Objectives: Although the effect of confounding factors on the studied outcome may be taken under consideration in stratified or multivariable analysis of the data, another approach is to adjust for the effect of such factors in the design of the study. We evaluated the available evidence from case-control studies in the field of antimicrobial resistance to identify the degree that matching was performed and the criteria used to do so.

Methods: We performed a systematic search of the PubMed database (articles archived by 08/2006) to identify relevant studies. Studies that used the individual matching technique were further analysed.

Results: 115 case-control studies with a focus on antimicrobial resistance were identified; 28 regarding A. baumannii, 25 regarding P. aeruginosa, and 62 for other bacteria. Individual matching was performed in 32 (27.8%) out of the 115 studies. Age was the most frequently used matching criterion in 22 of 32 (69%) evaluated matched case-control studies, while gender was used in 11 (34%), presence of underlying illness in 8 (25%), site of infection in 5 (16%), and area of residence in 4 studies (12.5%). Other criteria were used in less than 10% of the studies.

Conclusion: The available evidence from the analysed data from case-control studies in the field of antimicrobial resistance shows that individual matching is employed only in a proportion of such studies and only for a few characteristics, when it was used. The practical difficulties in finding appropriately matched control patients may contribute to this finding. Although there is a discussion regarding the risks of adjustment, we believe that methodological advances and more utilisation of the individual matching technique in case-control studies will help in answering important specific research questions in the field of antimicrobial resistance.