Infectious Diseases

Infectious diseases are illnesses that are caused by infection with a disease-causing organism, and can often be passed from one person to another. Infectious diseases vary greatly in severity, with symptoms that are mild and inconvenient, like the common cold, or those that are life-threatening, such as HIV/AIDS. Other familiar infectious diseases include chicken pox, meningitis, and streptococcal infection. Food poisoning, or foodborne illness, caused by salmonella, E. coli, and others, fall into this class of diseases. Symptoms of infectious diseases can be acute (short in duration) or chronic (long-lasting).

Persons with infectious diseases usually appear to be sick, although it is possible to harbor certain infectious diseases without having symptoms. The pathogens, or disease-causing agents, responsible for most infectious...