Clostridium difficile is responsible for 15-25% of cases of antibiotic-associated diarrhea (AAD) and for virtually all cases of antibiotic-associated pseudomembranous colitis (PMC). This anaerobic bacterium has been identified as the leading cause of nosocomial infectious diarrhea in adults and can be responsible for large outbreaks. Nosocomial C. difficile infection results in an increased length of stay in hospital ranging from 8 to 21 days. Risk factors for C. difficile-associated diarrhea include antimicrobial therapy, older age (>65 years), antineoplastic chemotherapy and length of hospital stay. Other interventions with high risk associations are enemas, nasogastric tubes, gastrointestinal surgery and antiperistaltic drugs. Prospective studies have shown that nosocomial transmission of C. difficile is frequent but often remains asymptomatic. Patients can be contaminated from environmental surfaces, shared instrumentation, hospital personnel hands and infected roommates. Once an outbreak starts, C. difficile may be spread rapidly throughout the hospital environment where spores may persist for months. Measures that are effective in reducing incidence of C. difficile infections and cross-infection include: (i) an accurate and rapid diagnosis, (ii) appropriate treatment, (iii) implementation of enteric precautions for symptomatic patients, (iv) reinforcement of hand-washing, (v) daily environmental disinfection, and (vi) a restrictive antibiotic policy. C. difficile is a common cause of infectious diarrhea and should be therefore systematically investigated in patients with nosocomial diarrhea.

27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR) spectroscopy at different magnetic fields was used to characterize the aluminum incorporation in the tetrahedral−octahedral−tetrahedral (Te−Oc−Te) structure of calcium silicate hydrates (C−S−H), which are the main constituents of the hydrated cement-based materials. C−S−H of different calcium/silicon ratio (0.66 < Ca/Si < 1.7) were synthesized in the presence of aluminum. Two different aluminum/silicon ratios (0.1 and 0.3) were tested. The maximum Al(IV)/[(Al(IV) + Si] ratio in the C−S−H that could be detected in these series of experiments was 0.17. Results show in this case that, when the tetrahedral sheet is formed by linear silicate chains, Al3+ preferentially substitutes a nonbridging Si4+. The rupture of the chains, caused by an increase of the Ca/Si ratio, makes such a position unstable and a redistribution of the aluminum in the tetrahedral sites occurs. Results also indicate that the substitution of Si4+ cannot take place when the tetrahedral sheet is composed of dimers (i.e., for high Ca/Si ratios). In these cases, Al3+ substitutes Ca2+ in the interlayer space (5-fold coordinated) and in the octahedral sheet (6-fold coordinated). However, this kind of substitution remains limited. The amount of aluminum incorporated in the C−S−H structure increases with the length of chains. Results confirm that C2AH8 is not a time-stable phase.