Overgrowth is defined as ≥105 potential pathogens per ml of saliva and/or per g of faeces. There are six ‘normal’ potential pathogens carried by healthy individuals and nine ‘abnormal’ potential pathogens carried by individuals with underlying disease both chronic and acute. Surveillance cultures of throat and/or rectum are required to identify overgrowth of ‘normal’ and/or ‘abnormal’ potential pathogens. There is a qualitative and quantitative relationship between surveillance samples and diagnostic samples of tracheal aspirate and blood, i.e., as soon as potential pathogens reach overgrowth concentrations in the surveillance samples, the diagnostic samples become positive for identical potential pathogens. Digestive tract decontamination aims at the eradication of overgrowth in order to prevent severe infections of lower airways and blood. Parenteral cefotaxime controls overgrowth of ‘normal’ bacteria, and enteral polyenes control overgrowth of ‘normal’ Candida species. Enteral polymyxin and tobramycin (with or without) vancomycin control ‘abnormal’ overgrowth.
Key words: overgrowth, ‘normal’ potential pathogens, ‘abnormal’ potential pathogens, surveillance samples, diagnostic samples, selective digestive decontamination (SDD)