This opinion piece fails to note three observations that remain unexplained among the broad range of interventions other than SDD that have been studied to prevent VAP.

Firstly, the VAP incidence within the SDD evidence base is unusual in two respects versus the evidence base for other methods of VAP prevention and versus observational studies; the mean VAP incidence in the control groups of SDD studies is >13 percentage points higher and the dispersion is greater than among control groups from studies of non-antibiotic methods of VAP prevention [1, 2]. Most strikingly, these disparities are most apparent among groups of VAP prevention studies rated with higher study quality due for example to study blinding achieved through the use of topical placebo [2]. Why?

Second, how does SDD work? It appears not to be through reductions in rates of Pseudomonas aeruginosa VAP [3].

Third, is it possible that the use of topical placebo is itself a vehicle for cross infection which is compounded by ecological effect associated with the use of SDD? If, as you report, colonization with antibiotic resistant Gram negative bacteria increases after cessation of SOD and SDD [4], would not this ecological effect carry over into periods of standard care and complicated the interpretation of even a cross over study [5]?

Until the fundamental question why the rates of VAP in control groups are generally higher than expected and yet this is not the case for non-antibiotic methods of VAP prevention then SDD has not been proven to be safe let alone effective.

1. Hurley JC. Profound effect of study design factors on ventilator-associated pneumonia incidence of prevention studies: benchmarking the literature experience. J Antimicrob Chemother 2008;61:1154–61.
2. Hurley JC. Paradoxical ventilator associated pneumonia incidences among Selective Digestive Decontamination studies versus other studies of mechanically ventilated patients. Benchmarking systematic review data. Crit Care 2011;15:R7.
3. Hurley JC. Lack of impact of Selective Digestive Decontamination on Pseudomonas aeruginosa ventilator associated pneumonia: benchmarking the evidence base. J Antimicrob Chemother 2011;66:1365-73
4. Oostdjik EAN, de Smet AMGA, Blok HEM, et al. Ecological effects of selective decontamination on resistant gram negative colonization. Am J Respir Crit Care Med 2010;181:452–7.
5. Raoofi M, Hurley JC. Selective Decontamination crossover study. Lancet Infectious Diseases 2012;12:179-80

Competing interests: None declared