R. VANFURTH Infection is an inseparable part of communal life, and infections are more common and more severe in hospital communi- ties because the sick are more easily infected than the healthy. However, even though progress in the medical sciences has meant that many more patients suftering from relatively severe diseases can be helped at present, the use of more sophisticated and complex treatment leads to impairment of the defence mechanisms in more patients than was the case ten to twenty years ago, and these patients are also more prone to develop an infection. Two questions are...