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M Bird, C Dawson, Y Miao, J Schachter, T Lietman; Does the Clinical Exam Adequately Identify Ocular Chlamydial Infection in Trachoma? . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3061.
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Purpose: Trachoma is a blinding eye disease caused by Chlamydia trachomatis. Current trachoma control programs utilize the prevalence of clinically active trachoma as a guide for antibiotic treatment of the chlamydial infection. We evaluated the validity of clinically determined active trachoma as a surrogate for chlamydial eye infection using the ligase chain reaction (LCR) to identify C. trachomatis. Methods: The sample population consisted of 1,059 subjects age 1-15 years from a clinical trial which compared mass treatment with oral azithromycin to topical tetracycline in a hyperendemic area of Egypt (the Azithromycin in the Control of Trachoma study, ACT). Using the WHO's simplified grading system for trachoma, participants were clinically active if they had 5 or more follicles (TF) or intense inflammatory infiltration (TI) on the central upper tarsal conjunctiva. At each exam conjunctival swabs were tested by LCR to detect C. trachomatis DNA. Results: The peak prevalence of both clinical activity, 120 of 190 (63%; 95% CI 56-70%), and infection, 110 of 186 (59%; CI 52-66%), occurred in 3 to 4 year olds and then decreased with age. Pretreatment, 110 of 355 (31%; CI 26-36%) clinically active children age 1-10 did not have infection by LCR. However, 108 of the 353 infected children (31%; CI 26-36%) were not clinically active. Only a single infection would have been missed using TF alone, thus using the TI grade in addition to TF added little benefit. The validity of the exam as a marker of infection decreased with age: among 1 to 5 year olds, 155 of 200 clinically active cases (78%; CI 71-83%) were infected, whereas among 11 to 15 year olds, only 15 of 85 clinically active cases (17%; CI 10-27%) were infected (Χ2 test, p<0.001). After treatment the clinical exam greatly overestimated the prevalence of infection; that is, the proportion of those clinically active who were infected declined from 244 of 355 (69%; CI 64-74%) pretreatment to 9 of 92 (10%; CI 5-18%) 14 months after treatment (Χ2 test, p<0.001). Conclusion: The clinical diagnosis of active trachoma is not always a reliable marker of infection; it is less reliable in teenagers and after treatment. Because trachoma control programs base the decision to treat on the prevalence of C. trachomatis infection, an alternate strategy could be to sample populations by one of the DNA amplification tests to detect infection. When laboratory testing is not available, clinical examination may be more useful if it is limited to a sentinel group of either 1-10 year olds or preferably 1-5 year olds.
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