• Clostridium difficile infection
• statins
• observational studies
• infectious diarrhoea

Statins are a class of lipid-lowering drugs which decrease cholesterol synthesis and have beneficial effects on cardiovascular disease. Observational studies have ascribed many other beneficial effects of statins, including reduced risk of infections, cancer and Alzheimer's.1 The authors argue that these myriad beneficial observations are plausible as ‘pleiotropic’ or multiple effects of statins including anti-inflammatory, antioxidant, immunomodulatory, antiapoptotic, antiproliferative, antithrombotic, antimicrobial and endothelium-protecting properties2 have been demonstrated in the laboratory. However, are these beneficial effects too good to be true?

It has been suggested that many of the apparent observed beneficial effects of statins can be explained by a ‘healthy user effect’. Statin users, especially compliant users, have been shown to be more likely to be insured, live at home, to have stopped smoking and to be more likely to engage in other positive health behaviours such as undergoing cancer screening and being vaccinated.3 ,4 Studies using administrative databases often are unable to adjust for these variables, and three studies on patients with pneumonia4–6 which adjusted for some of these variables found no decreased risk of pneumonia associated with current use of statins, and even reported a tendency towards increased risk.

Motzkus-Feagans and colleagues …