Upper Respiratory System Infections
ADVANCE ORGANIZER
We take into our lungs great quantities of air each day and some of that air contains infectious agents. Some of the time we get sick. Many different kinds of infections can produce the same symptoms and signs of disease.
Untreated skin or throat infections by Streptococcus pyogenes can occasionally result in serious kidney or heart damage, since these organs are not infected the damage is generally caused by the immune system.
In other infections, the disease can be the result of an exotoxin absorbed from a localized infection. The toxin then circulates causing damage at a distant site. Some toxins have specific target organs because they have receptors for specific cells in a specific organ.
ANATOMY AND PHYSIOLOGY
The functions of the upper respiratory tract include temperature and humidity regulation of inhaled air and removal of microorganisms. Included in the upper respiratory tract are the moist linings of the eyes, the nasolacrimal duct, the middle ears, sinuses, mastoid air cells, nose and throat. The first line of defense here is movement of mucus. This is accomplished by ciliated cells. Smoking and narcotics compromise the upper respiratory system.
NORMAL BIOTA
Nose and throat are colonized by alpha-hemolytic streptococci, nonhemolytic streptococci, Moraxell (Branhamella) catarrhalis, diphtheriods, and Bacteroides (an anaerobe!). The very exterior secretions of the nose are colonized by diphtheriods, micrococci and Staphylococcus aureus.
BACTERIAL INFECTIONS
Streptococcus pyogenes causes strep throat (also known as Streptococcal pharyngitis). This infection may lead to scarlet fever [see tongue], rheumatic fever or glomerulonephritis. Immunity is strain specific and there are many strains. About 80 different strains are identified by different M proteins.
Diphtheria is a toxin mediated disease caused by Corynebacterium diphtheriae. This is a non-motile, club shaped, non-sporing Gram positive rod which shows metachromatic granules. The potent toxin is produced as a result of lysogenic conversion. The toxin is then taken up by tissues such as the heart and nerves. The toxin irreversibly halts protein synthesis. It can be prevented by immunization.
Otitis media [middle ear infection] and sinusitis develop when infection with Streptococcus pneumoniae [a bile-soluble alpha hemolytic Gram-positive diplococci] or Haemphilus influenza [a small Gram negative rod requiring s and v factors to be virulent] extends beyond the nasopharynx. An upper respiratory viral infection usually precedes the bacterial infection. Sinusitis can also be caused by Bacteriodes species [these are small anaerobic Gram negative rods]. Meningitis is a possible complication of sinusitis.
Conjunctivitis (pink eye) is most usually caused by Haemophilus influenzae or by S. pnemoniae. However milder illnesses [that is, ones with less pus] often have viral causes (adenoviruses and rhinoviruses).
VIRAL INFECTIONS
Rhinoviruses are the most common cause of the common cold. [This is also known as acute afebrile infectious coryza]. Colds can pave the way for more serious infections.
Adenoviruses cause illnesses of varying severity some of which resemble strep throat [but do not, of course, respond to antibiotics].