BMC Public Health 2007, 7:356 http://www.biomedcentral.com/1471-2458/7/356 Table 1: Patient symptoms and medical history, associated with physicians' clinical suspicion of tuberculosis among smear-negative PTB suspects Clinical Suspicion of Tuberculosis Group Smear-Negative PTB suspects Symptoms and Medical History N = 151 (%) Low (N = 80) Intermediate (N = 25) High (N = 46) Suggestive chest radiographya Weight loss Cough Chest pain Dyspnea Tuberculosis exposure at home Hospital admission in the last 24 months Hepatitis Immune suppression b 42 (27.8%) 81 (53.6%) 135 (89.4%) 89 (58.9%) 105 (69.5%) 74 (49.0%) 53 (35.1%) 31 (20.5%) 51 (33.8%) 0 37 73 48 57 37 24 12 17 6 12 23 15 17 14 10 5 13 36 32 39 26 31 23 19 14 21 a: intake chest radiograph was suggestive of classical tuberculosis (upper-lobe fibrocavitary) disease. b: includes patients positive for the human immunodeficiency virus (27.2%) and those with a history of steroid use or cancer chemotherapy (3.6%) Analysis of pretest probability (clinical suspicion) for PTB Clinical features of SNPTB suspects are shown in Table 1. In 151 SNPTB suspects, according to risk categories, the prevalence of PTB in high, intermediate and low clinical pretest probabilities was 67.4% (31/46), 24% (6/25) and 7.5% (6/80), respectively (p < 0.05). The proportion of patients with a suggestive chest radiograph increased steadily in those with a clinical suspicion of TB groups; 0% of low probability patients had suggestive radio- graphs, 24% in the intermediate group, and 78% of the high level group (p < 0.001). Comparative performance analysis of tests The performance of tests for detection of MTB and diagno- sis of PTB are shown in Table 2. The PCR sensitivity was 65% (CI 95%, 50%–78%) and specificity was 83% (CI 95%, 75%–89%). When the pretest probability (Clinical Suspicion) is used as a diagnostic test, the high pretest probability sensitivity was 72% and specificity was 86%. The Intermediary pre- test probability sensitivity was 14% and specificity was 82%. The Low pretest probability sensitivity was 14% and specificity was 31%. PCR had a similar sensitivity to the culture results (65% vs 70%, p = 0.65) and to the high pretest probability (65% vs 72%; p = 0.66). The PCR dot-blot demonstrated 18 false-positive results (9 had TB in the past, 1 presented a scar image in the chest X-ray that resembled inactive TB, 4 were HIV+, 4 referred proximity with smear positive PTB cases in the last 6 months). The PCR dot-blot demon- strated 15 false-negative results. The value of the Kappa score obtained between the duplicates of PCRs was 100%. PCR dot-blot inhibition was found in one SNPTB suspect (2.3%). In a parallel evaluation, the sensitivity of PCR used in par- allel with the high pretest probability was higher than the sensitivity of the high pretest probability when used alone (90% vs 72%), and of culture sensitivity (90% vs 70%) (Table 2B). PCR colorimetric dot-blot assay, used in par- allel with the high pretest probability, had a PPV and NPV of 75% and 88%, respectively. The NPV was similar to that observed with culture alone (88% vs 89%). Compar- ing the SE and NPV of PCR used in parallel with the high pretest probability among those individuals not previ- ously treated and those treated for TB in the past, the fig- ures were respectively 91%, 90% vs 83%, 79%, p > 0.05. In HIV seropositive subjects, the sensitivity of PCR was 63% (CI 95%, 40%–82%), and specificity was 85% (CI 95%, 66%–94%). The PCR sensitivity was similar to that of culture (74%) and to the high pretest probability method (74%). The PCR colorimetric dot-blot assay, used in parallel with the high pretest probability, had a SE, SP, PPV and NPV of 90%, 65%, 72%, and 88%, respectively. In HIV seronegative subjects the sensitivity of PCR was 66%, and specificity was 83%. PCR sensitivity was similar to that of culture (67%) and to the high Pretest Probabil- ity method (71%). The PCR colorimetric dot-blot assay used in parallel with the high pretest probability had a SE, SP, PPV and NPV of 90%, 74%, 77%, and 89%, respec- tively. Considering the HIV status and comparing the SE and NPV of PCR with high pretest probability among those individuals not previously treated and those treated for TB in the past, the figures were respectively: 91%, 90%, and 89%, 88% for HIV seropositive subjects and 93%, 92% and 83%, 80% for HIV seronegative group. Page 4 of 10 (page number not for citation purposes)