Infectious Diseases - Most Frequently Reported Diseases, Resistant Strains Of Bacteria, Prevention Through Immunization, Influenza, Tuberculosis

Pursue him to his house, and pluck him thence; Lest his infection, being of a catching nature, Spread further.

—William Shakespeare, Coriolanus, 1608

Infectious (contagious) diseases are caused by microorganisms—viruses, bacteria, parasites, or fungi—transmitted from one person to another through casual contact, such as influenza; through bodily fluids, such as HIV (human immunodeficiency virus); or via contaminated food, air, or water supplies. Infectious diseases also may spread by vectors of disease such as insects or arthropods that carry the infectious agent.

Infectious diseases are a leading cause of death worldwide, according to the World Health Organization (WHO). Not long ago, the U.S. government and medical experts believed that widespread use of vaccines, antibiotics, and public health measures had effectively eliminated the public health threat of infectious diseases. Throughout the world, however, new and rare diseases are emerging, and old diseases are resurfacing. Some of these infections reflect changes associated with increasing population, growing poverty, urban migration, drug-resistant microbes, and expanding international travel.

The mistaken belief that infectious diseases were problems of the past prompted the governments of many countries, including the United States, to neglect public health programs aimed at preventing and treating infectious disease. By 1994, however, enough troubling new diseases had arisen and old ones recurred that a federal commission recommended that the United States spend $125 million to implement a plan to respond to and contain infections.

The Centers for Disease Control and Prevention (CDC) tracks certain infectious diseases ("notifiable diseases") for the U.S. Public Health Service (PHS). The CDC defines a notifiable disease: "A notifiable disease is one for which regular, frequent, and timely information regarding individual cases is considered necessary for the prevention and control of the disease." The list of nationally notifiable diseases is revised periodically. For example, a disease might be added to the list as a new pathogen (an organism that causes disease) emerges, or a disease might be deleted as its incidence declines. Physicians, clinics, and hospitals must report any occurrences of these diseases to the CDC each week. Table 7.1 shows the nationally notifiable infectious diseases tracked in 2006.