Clinical diagnostic performance of the simultaneous amplification and testing methods for detection of the Mycobacterium tuberculosis complex for smear-negative or sputum-scarce pulmonary tuberculosis in China

Background Early detection of pulmonary tuberculosis （PTB） is a big challenge in smear negative and sputum scarce patients in China.Simultaneous amplification and testing methods for detection of the Mycobactedum tuberculosis （MTB） complex （SAT-TB assay） is a novel molecular technique established in our hospital.This method has a high sensitivity and specificity in the lab.In this study,the clinical diagnostic performance of this method in smear-negative or sputum-scarce PTB suspects was investigated and evaluated.Methods Two hundred smear negative and 80 sputum-scarce patients were recruited in this study.Samples that included sputum or bronchial washing fluid were collected and sent for both bacteria culture and SAT-TB assay.Diagnosis for these patients was based on the comprehensive evaluation of chestX-ray/CT study,histology examination,lab results,and treatment response.Sensitivity,specificity,positive predictive value （PPV） and negative predictive value （NPV） for each diagnostic test were investigated and calculated using confirmed tuberculosis （TB） and non-TB cases.The time required for detection of MTB was also measured for each method.Results Ninety-two patients （33％） were diagnosed as definitive TB,112 patients （40％） were probable PTB,and 76 （27％） were non-TB.The sensitivity,specificity,PPV,and NPV of SAT-TB in smear-negative PTB suspects were 93％ （95％ CI,84％-98％）,98％ （95％ CI,90％-100％）,98％ （95％ Cl,91％-100％）,and 93％ （95％ CI,83％-98％）.In sputum scarce PTB suspects,the sensitivity,specificity,PPV,and NPV of the SAT-TB assay on bronchial washing fiuids were 90％ （95％Cl,74％-98％）,100％ （95％ Cl,85％-100％）,100％ （95％ Cl,88％-100％）,and 88％ （95％ CI,69％-97％）.The accuracy of the SAT-TB assay is consistent with the bacteria culture assay.The median time required for detecting MTB in the SAT-TB assay was 0.5 day,which was much faster than bacteria culture （28 days）.Conclusions The SAT-TB assay is a fast and accurate method for the detection of MTB.It can be widely applied in the clinic and be an asset in early detection and management of PTB suspects,especially in those patients who are smear negative or sputum scarce.

Computed tomography in predicting smear-negative pulmonary tuberculosis in AIDS patients

Background The correct diagnosis of sputum smear-negative pulmonary tuberculosis in AIDS patients is very important to their therapy. We aimed to assess the value of the computed tomography （CT） and clinical findings in predicting smear- negative pulmonary tuberculosis in AIDS patients. Methods A total of 121 AIDS patients suspected of smear-negative pulmonary tuberculosis by clinical and radiographic findings were recruited. Pulmonary tuberculosis was diagnosed in 57 （47.1%） patients. The CT and clinical predictors were selected to diagnose AIDS-related pulmonary tuberculosis through univariate and multivariate Logistic analysis. Results Multivariate analysis showed that five variables, including weight loss, presence of miliary nodules, necrotic lymph node, Iobular consolidation, tree-in-bud sign, were independent predictors of pulmonary tuberculosis in AIDS patients. Predicted scores based on the five variables were used to identify pulmonary tuberculosis. If the predicted score of 3 was taken as the ideal cut-off point in the diagnosis of AIDS-related smear-negative pulmonary tuberculosis, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 84.2%, 81.2%, 80.0%, 85.2%, and 82.6%, respectively. Conclusion The prediction method based on five key factors of clinical and CT findings are useful in guiding the diagnosis of smear-negative pulmonary tuberculosis in AIDS patients.

Usefulness of interferon-γrelease assay for the diagnosis of sputum smear-negative pulmonary and extra-pulmonary TB in Zhejiang Province,China

Background:Quick diagnosis of smear-negative pulmonary tuberculosis(TB)and extra-pulmonary TB are urgently needed in clinical diagnosis.Our research aims to investigate the usefulness of the interferon-γrelease assay(IGRA)for the diagnosis of smear-negative pulmonary and extra-pulmonary TB.Methods:We performed TB antibody and TB-IGRA tests on 389 pulmonary TB patients(including 120 smear-positive pulmonary TB patients and 269 smear-negative pulmonary TB patients),113 extra-pulmonary TB patients,81 patients with other pulmonary diseases and 100 healthy controls.Blood samples for the TB-Ab test and the TB-IGRA were collected,processed,and interpreted according to the manufacturer’s protocol.Results:The detection ratio of smear-positive pulmonary TB patients and smear-negative pulmonary TB patients were 90.8%(109 of 120)and 89.6%(241 of 269),respectively.There was no statistically significant difference of its performance between these two sample sets(P>0.05).The detection ratio of positive TB patients and extra-pulmonary TB patients were 90.0%(350 of 389)and 87.6%(99 of 113),respectively,which was not significantly different(P>0.05).Conclusions:In this work,the total detection ratio using TB-IGRA was 89.4%,therefore TB-IGRA has diagnostic values in smear-negative pulmonary TB and extra-pulmonary TB diagnosis.

Improved ZiehI-Neelsen Microscopy： Bleach Sputum Smear Negative Specimens after Centrifugation

Background： Direct ZN （Ziehl-Neelsen） sputum smear microscopy for diagnosis of TB （tuberculosis） has low sensitivity, especially in TB/HIV co-infected patients. Sputum concentration by bleach （NaOCI） with sedimentation has been used to increase the sensitivity of sputum smear microscopy in many settings but with varying results. Objective： To determine whether bleach plus centrifugation significantly improves the detection of AFB （acid-fast bacilli） in ZN smear-negative sputum specimens. Methods： Three hundred and seventy sputum specimens were collected from new TB suspects attending a Nairobi referral district hospital and processed for direct microscopy using ZN technique and culture on Lowenstein Jensen Media. All smear-negative specimens were treated with 3.5% bleach and left to stand for 30 min before centrifugation. The bleach treated smears were processed and examined using ZN technique. Results： Of the 370 specimens, 200 （54%） were positive culture. The number of sputum samples that were smear-positive by direct ZN was 138 （37.2%）, with a sensitivity of 66%. After treatment of direct ZN smear-negative specimens with 3.5% bleach and centrifugation, the total number of AFB smear-positive samples increased to 171 with an increase in sensitivity of 66% to 81.1% （15.1%）. Conclusion： In this study, bleach with centrifugation significantly increased the yield of sputum smear microscopy. Further evaluation of these techniques in routine programmes is required especially in settings where the burden of TB/HIV is high.