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Genital Gram Stains Unreliable As STI Detectors


 

WASHINGTON — Genital Gram stains alone lack the diagnostic ability to detect Chlamydia trachomatis and Neisseria gonorrhoeae infections, based on data from 1,511 emergency department visits, reported Dr. Shanda Riley in a poster at the annual meeting of the American College of Emergency Physicians.

In 502 visits (33%), physicians used a DNA probe without a Gram stain, 68 visits (5%) included a Gram stain without a DNA probe, and 941 visits (62%) included both a Gram stain and a DNA probe to detect sexually transmitted infections.

Dr. Riley of the University of Illinois, Peoria, and her colleagues reviewed all DNA probes for C. trachomatis and N. gonorrhoeae, along with Trichomonas vaginalis wet preps and genital Gram stains performed on patients seen in an emergency department between January 2004 and December 2004. The sensitivity and the specificity of the Gram stains were 71.1% and 41%, respectively, for N. gonorrhoeae, and 75.6% and 43%, respectively, for C. trachomatis. In addition, the average positive predictive value of the Gram stains for both organisms was 15%. Gram stains were considered positive if they demonstrated more than 10 white blood cells per high-power field or if clue cells, Gram-negative intracellular/extracellular diplococci, or T. vaginalis organisms were found.

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