The innovative microbiology of selective digestive decontamination requires a new mindset – Letter to the editor

Dear Editor, After 30 years of selective digestive decontamination (SDD) research, the lack of generally accepted definitions and concepts on infection and infection control still hinders a constructive discussion. The recent review by Muskiet et al.1 and the related editorial2 suggest a disturbing lack of understanding of the essentials of the classical SDD strategy. More specifically, both authors fail to discuss the classification of infections, crucial for any infection surveillance program and the classification of microorganisms according to their pathogenicity. Furthermore, important concepts such as carrier state, overgrowth and the distinction between carriership, colonisation and infection are lacking. Finally, neither Muskiet nor Van Essen gave an indication of knowledge of the four components of the SDD strategy, thereby reducing this life-saving strategy to administration of antibiotics in throat and gut. As with all ICU interventions, a thorough knowledge and appreciation of at least the basics behind an intervention is required. Armed with the insights a sound judgment on the available literature on resistance during SDD is possible. Important concepts3 in the SDD strategy include ‘normal’ versus ‘abnormal’ potentially pathogenic microorganisms (PPM) and the carrier state classification of infection. ‘Normal’ PPM include S. pneumoniae, H. influenzae, M. catarrhalis in the throat, E. coli in the gut, and S. aureus and C. albicans in throat and gut. They are carried by healthy individuals. In contrast, only diseased individuals carry abnormal PPM consisting of eight aerobic Gram-negative bacilli (Klebsiella, Enterobacter, Citrobacter, Proteus, Morganella, Serratia, Acinetobacter, and Pseudomonas spp) and methicillin-resistant S. aureus (MRSA). The carrier state concept allows the distinction between three types of infection (table 1): Primary endogenous infection is defined as an infection caused by potential pathogens present in overgrowth concentrations in the admission flora. It is the most common intensive care unit (ICU) infection (55%) and develops within one week of admission. The innovative microbiology of selective digestive decontamination requires a new mindset – Letter to the editor