SECTION I
Outbreaks of Diseases of the Respiratory Tract
For full indeed is earth of woes, and full the sea; and in the day as well as night diseases unbidden haunt mankind, silently bearing ills to men.
Hesiod,Works and Days, ca. line 101(Trans., J. Banks, 1856)
Among those who require a visit to a physician, infections of the respiratory system are the most common reason for the visit. These respiratory infections account for an average of ~80 physician visits per 100 persons each year. Infections of the lower respiratory tract, such as pneumonia and influenza, are also the leading cause of death by infectious disease worldwide. Pneumonia, influenza, and tuberculosis result in about 4.3 million deaths per year.
Containment of a respiratory outbreak can be complicated by a pathogen’s ability to survive outside the body. For example, some cold‐causing viruses can remain infective on an environmental surface for several hours. This makes classroom desks and doorknobs potential fomites for the spread of disease. Pathogens on the hands can be inoculated into the eyes and drain into the nose. There they can attack and initiate a respiratory tract infection. Consequently, one important way to decrease spread of respiratory pathogens is to wash hands frequently and to avoid touching the eyes.
The primary method of spread for respiratory tract pathogens is via airborne particles and mucus droplets. Airborne particles can travel over 1 meter through the air and still remain infectious, while mucus droplets travel less than 1 meter through the air. As a result, respiratory pathogens are highly contagious and spread rapidly through a community. Outbreaks of respiratory pathogens are common in colleges. Students who occupy college residence halls usually share rooms with one or more students and are in contact with hundreds of students at sporting events, in recreational facilities, and in classrooms. As a result, the number of opportunities for transmission of respiratory pathogens is greatly increased relative to others who live at home. The frequency of transmission of respiratory pathogens is significantly higher during cold‐weather periods, when students are restricted to indoor activities. Therefore, annual winter outbreaks of colds, influenza, strep throat, and bronchitis in this setting are common.
Although several thousand microbes are inhaled each day, the defenses of the respiratory system are very efficient and regularly prevent infection and disease. Mucus is secreted by goblet cells within the respiratory epithelium. This mucus traps most microbes before they travel deep into the respiratory tract. It helps to inhibit attachment of microbes to host cell receptors. Microbes that are trapped in the mucus are swept out of the respiratory system by cilia on the surface of the pseudostratified epithelium. The mucus is swallowed, and the microbes are destroyed in the digestive system. In addition, the mucus has a high concentration of dissolved solutes. The hypertonic environment thus created inhibits the growth of most cellular microbes—bacteria, fungi, and protozoa. In the alveoli of the lungs, macrophages are present to phagocyt