INFECTIOUS DISEASES have always played a major role in defining our daily lives. Empires have risen and fallen from events related to contagious diseases. Human and animal populations have been devastated—and controlled—by the outbreak of epidemic infectious diseases. The last century and a half has brought great understanding of the biology of microbial agents affecting man and his environment. With this knowledge, we have had periods of extreme optimism regarding man's ability to control and even conquer the pestilences affecting our health. However, this euphoria about man's ability to positively influence our interaction with our microbiological environment is often followed by periods where we doubt the long-term effect of our interactions.
During the last century, we have seen a marked reduction in the prevalence of many infectious diseases that used to carry a high morbidity and mortality. Severe disease related to infection with group A streptococci such as erysipelas, rheumatic