Traditionally only those physicians with many years of experience in a particular speciality chose to commit their accumulated knowledge to print for general consumption. Although of relatively tender years I can remember and sympathize with the problems of learning the 'Infectious Disease Trade' as a medical student and later as a junior hospital doctor. This book is an attempt to journey through and remedy my ignorance-in­ retrospect. I have thus attempted to provide an unashamedly clinical intro­ duction to Infectious Diseases which is of particular interest and use to medical students and junior hospital staff, especially those about to enter General Practice. I hope I have succeeded. Suggested further reading Christie, A. B. (1974). Infectious Diseases: Epidemiology and Clinical Practice. (Edinburgh: Churchill Livingstone) Hoeprich, P. D. (1977). Infectious Diseases. (London: Harper and Row) Ramsay, A. M. and Emond, R. T. D. (1978). Infectious Diseases. (London: Heinemann Medical Books) Youmans, G. P. , Paterson, P. Y. and Sommers, H. M. (1975). The Biologic and Clinical Basis of Infectious Disease. (W. B. Saunders Company) 1 1 Infection and infectious diseases: basic principles INTRODUCTION Infection may be defined as an abnormal state caused by multiplication of pathogenic microorganisms in or on the body of a host: this may cause disease, have no observable effect, or may even be of benefit to an infected host.