This week we discussed upper and lower respiratory tract infections. When diagnosing infections of the respiratory tract, normal flora in the throat must be considered. Coagulase negative Staphylococcus, diphtheroids, Viridans streptococcus, and Neisseria spp are the most common normal flora found in the throat. The main cause of pharyngitis and tonsillitis is viruses however the when the cause is bacterial the etiologic agent is usually Streptococcus pyogenes. If S. pyogenes is suspected there is a rapid direct antigen test that can be done. The first step is extraction of the antigen with enzymes. The antigen in solution if present then reacts with the antibody to give a positive result. If positive the report should say “positive for Group A Streptococcus antigen” and the patient should be treated. If negative the report should say “negative for Group A Streptococcus antigen” and the specimen should be cultured. Most of these rapid tests are chromatographic immunoassays.
Lower respiratory tract infections include bronchitis, bronchiolitis, and pneumonia. Possible pathogens include S. pneumonia, S. aureus, Klebsiella pneumonia, p. aeruginosa, and H. influenza. Definite pathogens are M. tuberculosis, M. pneumonia, and Legionella. Legionella is primarily found in water and is transmitted by inhalation of infectious aerosols. It was first isolated after an America Legion Convention in which a large number of people began to show nonspecific symptoms including fever, shills, cough, myalgia, headache, chest pain, and diarrhea. Pneumonia and other organ involvement can also be seen. Infection with Legionella was given the name Legionairre’s Disease. Pontiac fever is similar to Legionairre’s disease however there is no pneumonia and no organ involvement.
Here is a picture that shows how Legionella pneumophila replicates inside a host phagocyte.
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