title: The effect of control group selection in the analysis of risk factors for extended spectrum beta-lactamase-producing Klebsiella pneumoniae infections. A prospective controlled study.
abstract: The aim was to evaluate the effect of control selection on risk factor analysis for extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) infections. Four contemporaneous case-control studies were conducted prospectively with 372 patients: Study 1 (ESBL-KP-infected vs non-infected); Study 2 (ESBL-KP-infected vs non-ESBL-KP-infected); Study 3 (all KP-infected vs non-infected); Study 4 (non-ESBL-KP-infected vs non-infected). Time at risk (TAR, i.e. duration of hospital stay) was the most significant risk factor [Study 1: odds ratio (OR): 5.74 (95% CI: 2.26-14.59; P<0.001); Study 2: 3.52 (1.47-8.43; P=0.005); Study 3: 2.68 (1.57-4.58; P<0.001)]; central venous catheterisation (CVC) was a risk factor in Study 1: 5.31 (1.67-16.82; P=0.005) and Study 3: 2.10 (1.04-4.27; P=0.04). Prior use of cephalosporins (PUC) was a risk factor only in studies with non-infected patients as controls [Study 1: 5.64 (1.90-16.72; P=0.002) and Study 3: 4.60 (2.09-10.13; P<0.001)]. The ORs were uniformly lower with 'non-ESBL-KP-infected' (TAR: 3.52; CVC: 2.07; PUC: 1.97) compared with 'non-infected' patients (TAR: 5.74; CVC: 5.31; PUC: 5.64) as control groups. Selection of control patients has a crucial role in the evaluation of risk factors for ESBL-KP infections. A consistent underestimation of the magnitude of the risk factors is observed when the control group is defined by the non-ESBL-KP-infected patients.
authors.affiliation: Department of Internal Medicine, Section of Infectious Diseases, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre (FFFCMPA), Porto Alegre, RS, Brazil. behar@fffcmpa.edu.br
authors.forename: P R P
authors.initials: PR
authors.lastname: Behar
authors.forename: P J Z
authors.initials: PJ
authors.lastname: Teixeira
authors.forename: J M G
authors.initials: JM
authors.lastname: Fachel
authors.forename: A C
authors.initials: AC
authors.lastname: Kalil
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D015982:Bias; D001938:Brazil / Q000453:epidemiology; D016022:Case-Control Studies; D035061:Control Groups; D003428:Cross Infection / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D004866:Equipment Contamination; D006801:Humans; D007710:Klebsiella Infections / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000201:enzymology* / Q000302:isolation & purification; D007902:Length of Stay; D016015:Logistic Models; D018579:Patient Selection; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D001618:beta-Lactamases / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D001618:beta-Lactamases