Value of tuberculin test in screening tuberculosis infection in HIV infected/AIDS patients in Butuo County,Sichuan Province

Objective To analyze the application value of tuberculin (PPD) test in screening tuberculosis infection in HIV infected/AIDS patients in Butuo, Liangshan Yi Autonomous Prefecture. Methods A total of 688 patients who were followed up and had taken immunosuppressant therapy >1 month were enrolled, among 2159 HIV/AIDS patients managed in the “Thirteenth Five-Year Plan” National Science and Technology Major Project in Jiudu, Mu’er and Te Muli Town in Butuo between December 2018 and August 2019. Questionnaire, PPD test, X-ray chest and CD4⁺ T lymphocyte count were conducted. MTB etiology test was performed on eligible subjects. Of the 688 cases, 175 were without verification of PPD test results, 40 were not examed by X-ray and had no etiology basis, 7 were infected by nontuberculous mycobacteria, and 466 cases were included finally. SPSS 21.0 software was used to analyze the PPD test results (the average diameter of skin scleroma ≥5 mm was positive) and the status of active pulmonary tuberculosis or latent tuberculosis infection (LTBI) judged by the expert group, to detect the efficiency of PPD test for active pulmonary tuberculosis (including sensitivity, specificity, positive predictive value, negative predictive value, agreement rate) based on diagnosed active pulmonary tuberculosis cases. The relationship between positive rate of PPD test and whether complicated with active pulmonary tuberculosis or not, as well as comparison of different CD4⁺ T lymphocyte counts and prevalence, were detected by χ² test. P<0.05 was statistically significant. Results Among the 466 patients, 377 (80.90%) were negative in PPD test, 14 (3.00%) were generally positive, 29 (6.23%) were moderately positive, 46 (9.87%) were strongly positive and the positive rate was 19.10% (89/466), all of them were consistent with tuberculosis infection. By tuberculosis screening and diagnosis from expert group, 89 cases (19.10%) were active pulmonary tuberculosis, including 57 LTBI cases (12.23% (57/466)). Based on diagnosis from expert group, the sensitivity, specificity and consistent rate of PPD test for active tuberculosis were 35.96% (32/89), 84.88% (320/377), and 75.54% (352/466), respectively. The positive rate of PPD test in HIV/AIDS patients complicated with active pulmonary tuberculosis was significantly higher than that in patients without active pulmonary tuberculosis (35.96% (32/89) vs. 15.12% (57/377);χ²=20.827, P=0.000). Furthermore, only when CD4⁺ T lymphocyte count was more than 500 count/μl, the complicated rate was significantly higher (52.00% (13/25) vs. 16.67% (19/114); χ²=14.444, P=0.000). Conclusion As the sensitivity of PPD test to detect active tuberculosis was not high, other examinations should be combined.But the positive rates of PPD test was positively correlated with the count of CD4⁺T lymphocytes,and the specificity was high, negative results may also indicate non-tuberculosis infection. Therefore, it may still be used as an effective method in areas with high HIV prevalence and limited health resources.