Indications The main reason to culture a throat specimen when you suspect streptococcal pharyngitis is to avoid needless therapy and expense: Viruses have traditionally been blamed in most cases of acute pharyngitis, and one recent study suggests that Chlamydia trachomatis and Mycoplasma pneumoniae may be responsible for 20% and 10%, respectively, of pharyngitis in adults. Group A [beta]-hemolytic streptococci cause about 20% of childhood pharyngitis and only 5% of adult pharyngitis. Although there has been a great deal of controversy about the role of penicillin in reducing symptoms of group A [beta]-hemolytic strep pharyngitis, a recent study suggests that early therapy with penicillin does decrease persistence of symptoms.
While current evicence is insufficient to ermit adequate evaluation of the rapid strep tests, a developing practice today is to treat when the quick test is positive and culture when the quick test is negative (see "Some quick strep tests in profile," page 97). If early treatment does reduce the duration of pharyngitis, the rapid tests may have an important role in the office lab. Indications for culture are:
* Sore throat with high fever (particularly in children), tonsillar exudate, tenderness and swelling of the lymph nodes in the neck, or scarlatiniform rash
* Contact with persons who have proved streptococcal pharyngitis.
* Pharyngitis and a history of rheumatic fever
Collection As a rule, if the patient doesn't gag and isn't uncomfortable while the sample is collected, the specimen is probably inadequate. Advise whoever takes the throat specimen to try this procedure:
1. Ask the patient to open wide and "pant like a dog." You can get kids to do this by panting along to show them how.
2. Depress the tongue with a tongue blade.
3. As quickly as possible, place the swab in the area of one of the tonsils (tonsillar pillar), then streak the swab briskly across the back of the throat and across the other tonsillar pillar. Although texts often describe a slow, well-visualized process that includes evaluation for exudate, you usually have no more than a few seconds to collect your sample--especially in children. You should suspect inadequate sample collection if your plate shows very little growth.
If the samples are taken with a sterile cotton swab, plate the specimen within two hours of collection. Collecting the specimen with a special sampling device (Culturette) is more expensive, but such devices contain a medium that will preserve group A strep. They allow plating of the day's cultures at a single sitting with...
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