Infections play a major role in daily medicine and are the leading cause of death in global statistics. They continually present us with difficult problems: resistance development, new pathogens, new diseases from known pathogens, new pathogenic strains of symbiotic pathogens, an increase in opportunistic infections, new infection spaces (tampons, air conditioning systems, implant surfaces, aquaculture systems, etc.), new technical vectors, new hosts.

Despite the efforts of some authors in recent years to emphasize the indisputably vital role of symbiosis with bacteria, the fact remains that symbiotic pathogens can "terminate the symbiosis" on occasion and cause endogenous infections, which in turn account for 70% of nosocomial infections.

From the perspective of biological evolution, it is incomprehensible. Infection: an accident of evolution, a misunderstanding between pathogen and host, or a degeneration of symbiosis?