Corneal scrapings are useful for the diagnosis of infection caused by

Corneal scrapings are useful for the diagnosis of infection caused by

• A. Chlamydia trachomatis
• B. Ehrlichia chaffeensis
• C. Mycoplasma hominis
• D. Rickettsia prowazekii

Answer: (A)

Corneal scrapings are most informative when the infection is caused by an organism that lives in ocular surface epithelial cells and can be detected directly or in cultured cells from the eye. Chlamydia trachomatis fits this scenario because it causes conjunctivitis and keratitis and is an obligate intracellular bacterium that does not grow on standard media. Diagnosis from eye scrapings relies on seeing intracellular inclusions in epithelial cells, or on culture in specialized cell lines (like McCoy cells), or on nucleic acid–based tests. The other organisms listed do not typically involve the eye in this way and are diagnosed by methods using blood or genitourinary specimens rather than corneal tissue. Thus, corneal scrapings are most useful for diagnosing Chlamydia trachomatis infections.

Corneal scrapings are most informative when the infection is caused by an organism that lives in ocular surface epithelial cells and can be detected directly or in cultured cells from the eye. Chlamydia trachomatis fits this scenario because it causes conjunctivitis and keratitis and is an obligate intracellular bacterium that does not grow on standard media. Diagnosis from eye scrapings relies on seeing intracellular inclusions in epithelial cells, or on culture in specialized cell lines (like McCoy cells), or on nucleic acid–based tests. The other organisms listed do not typically involve the eye in this way and are diagnosed by methods using blood or genitourinary specimens rather than corneal tissue. Thus, corneal scrapings are most useful for diagnosing Chlamydia trachomatis infections.