If you ask the average person how microbes (or germs) impact their lives, they would immediately think of disease. Figure 1-16 shows a number of important pathogens. This is not a silly view, as pathogenic microorganisms have greatly affected human populations throughout our existence. In 1900 in the United States the infant mortality rate was near 50%, mostly due to childhood infectious disease and until about 1930, microbes were the major cause of death in humans. From today???s perspective this is a horrendous statistic, over half of all infants did not make it to adulthood! With the advent of antibiotics, vaccines and better water sanitation, humanity has reduced the impact of pathogenic microbes in developed countries, but they will always remain an important social concern. The discipline of microbiology emerged from the study of these diseases, and most advances in treating various ailments had their roots in this relatively young science.

While death from infectious disease in the U. S. has been greatly diminished, infection rates in developing nations remain unacceptably high. "Ancient" diseases continue to be a problem where nutrition and sanitation are poor, and emerging diseases such as Acquired Immunodeficiency Syndrome (AIDS) are even more dangerous for such populations. The Centers for Disease Control and Prevention (the U.S. government agency charged with protecting the health and safety of people) estimates that about 9% of adults between the ages of 18-49 in Sub-Saharan Africa are infected with HIV, AIDS is only one of a number of new diseases that have emerged. Many of these diseases have no known cure. Influenza and pneumonia are leading killers of the elderly even in the U. S. and other developed nations. Even the common cold causes illness and misery for almost everyone and drains the productivity of all nations. Many of the new diseases are viral in nature, making them notoriously difficult to treat.

Disease due to food-borne pathogens also remains a problem, largely because of consumption of improperly processed or stored foods. Understanding the sources of contamination and developing ways to limit the growth of pathogens in food is the job of food microbiologists.