JAC Advance Access originally published online on March 8, 2008
Journal of Antimicrobial Chemotherapy 2008 61(5):1154-1161; doi:10.1093/jac/dkn086
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Original research |
Profound effect of study design factors on ventilator-associated pneumonia incidence of prevention studies: benchmarking the literature experience
1 School of Rural Health, University of Melbourne, Australia 2 Infection Control Units, Ballarat Health Services and St John of God Hospital, Ballarat, Australia 3 Division of Internal Medicine, Ballarat Health Services, PO Box 577, Ballarat, Victoria 3353, Australia
Received 30 December 2007; returned 23 January 2008; revised 6 February 2008; accepted 11 February 2008
* Correspondence address. Internal Medicine Service, Ballarat Health Services, PO Box 577, Ballarat, Victoria 3353, Australia. Tel: +61-3-53-204322; Fax: +61-3-53-204472; E-mail: jamesh{at}bhs.org.au
Background: The ventilator-associated pneumonia incident proportion (VAP-IP) is highly variable among control groups of studies of methods for its prevention. The objective here is to develop and validate a literature-derived benchmark against which these groups can be profiled.
Methods: A literature search yielded 95 cohort groups and control and intervention groups of 150 studies of either non-antimicrobial or antimicrobial methods of VAP prevention. The 95 cohort groups comprise a benchmark set (30 groups), from which the reference funnel plot (RFP) was derived, and a search set (65 groups), against which the benchmark was validated. The VAP-IP data of the benchmark set were found in five published systematic reviews, whereas the VAP-IP data of the search set were abstracted directly from the literature.
Findings: Among the 95 cohort groups, the VAP-IP of groups with size >399 was significantly lower than the VAP-IP of smaller groups. Compared with the RFP, 15 of 51 (29%) control groups from studies of antimicrobial methods of VAP prevention with concurrent design were high outlier versus 2 of 110 (2%) control groups from other types of study design (P < 0.001). There were only 22 (14%) outlier groups, all low outlier, among the 162 intervention groups.
Conclusions: Study design factors such as concurrency and study size have potentially greater influence on the VAP-IP than do the VAP prevention methods under study. The outlier status of control groups were inapparent in the individual studies and the meta-analyses and yet would have confounded the estimates of treatment effect.
Keywords: antimicrobial prophylaxis , cross-infection , funnel plots