Direct fluorescent antibody assay and polymerase chain reaction for the detection of Chlamydia trachomatis in patients with vernal keratoconjunctivitis

OBJECTIVES To identify Chlamydia trachomatis via polymerase chain reaction and a direct fluorescent antibody assay in patients with vernal keratoconjunctivitis while comparing the efficacies of both tests for detecting Chlamydia trachomatis in these conditions. METHODS Conjunctival scraping samples were obtained from 177 patients who were divided into two groups: a vernal keratoconjunctivitis group (group A) and a control group (group B). The polymerase chain reaction and a direct fluorescent antibody assay were performed. Sensitivity, specificity, receiver operating characteristic curves, and areas under the curve were calculated for both tests in groups A and B. Receiver operating characteristic curves were plotted using a categorical variable with only two possible outcomes (positive and negative). RESULTS Statistical analysis revealed a significant association between vernal keratoconjunctivitis and Chlamydia trachomatis infection detected by a direct fluorescent antibody assay with high sensitivity and specificity. All patients in group A with positive polymerase chain reactions also presented with positive direct fluorescent antibody assays. CONCLUSION The association between vernal keratoconjunctivitis and Chlamydia trachomatis infection was confirmed by positive direct fluorescent antibody assays in 49.4% of vernal keratoconjunctivitis patients and by positive polymerase chain reactions in 20% of these patients. The direct fluorescent antibody assay detected Chlamydia trachomatis in a higher number of patients than did the polymerase chain reaction. Although the diagnosis of trachoma is essentially clinical, the disease may not be detected in vernal keratoconjunctivitis patients. Due to the high frequency of chlamydial infection detected in patients with vernal keratoconjunctivitis, we suggest considering routine laboratory tests to detect Chlamydia trachomatis in patients with severe and refractory allergic disease.