Section I. EPIDEMIOLOGY OF RESPIRATORY DISEASES
Causative agents for respiratory diseases of military importance include certain viruses,
bacteria, fungi, and rickettsiae. On the basis of symptoms and mode of transmission,
the respiratory diseases may be classified into three categories: respiratory tract
symptoms/ transmission by discharges from nose and mouth; transmission from
infectious materials from the air; transmission by discharges from nose and throat with
symptoms not localized in the respiratory tract.
a. Diseases with Symptoms Localized in the Respiratory Tract. For some
diseases, the symptoms are localized in the respiratory tract, and the diseases are
transmitted by discharges from the nose and mouth. Such diseases include the
common cold, diphtheria, influenza, bacterial pneumonia, streptococcal sore throat,
tuberculosis, and others.
b. Diseases Transmitted Through Inhalation of Infectious Material from the
Air. These are diseases transmitted through inhalation of infectious material from the
air but not necessarily coming from discharges of the respiratory tract. Included are
smallpox, coccidioidomycosis, Q fever, and others.
c. Transmission by Discharges from Nose and Throat/Symptoms not
localized in the Respiratory Tract. These are diseases spread by discharges from
the nose and throat but symptoms of which are not localized in the respiratory tract.
Included are measles, mumps, meningococcal meningitis, scarlet fever, and, again,
FACTORS IN TRANSMISSION: GENERAL FACTORS
Respiratory disease agents carried in respiratory discharges apparently are transmitted
by one of two means: droplets and droplet nuclei.
a. Droplet Transmission
(1) Distance droplets travel. In the normal course of respiration, a person
exhales droplets of moisture that are on the order of 50 microns in size. These droplets
usually travel about 4 to 5 feet horizontally from their point of release in air before
rapidly falling out because of their weight. If forcibly expelled, as in sneezing or
coughing, they may travel much farther.