Sopa Srisungngam

LightCycler real-time PCR for rapid detection and quantitation of Mycobacterium leprae in skin specimens.

Diagnosis of leprosy is usually based on clinical features and skin smear results including the number of skin lesions. Mycobacterium leprae is not cultivable and bacterial enumeration by microscopic examination is required for leprosy classification, choice in choosing and monitoring chemotherapy regimens, and diagnosis of relapse. However, detection and quantification using standard microscopy yields results of limited specificity and sensitivity. We describe an extremely sensitive and specific assay for the detection and quantification of M. leprae in skin biopsy specimens. Primers that amplified a specific 171-bp fragment of M. leprae 16S rRNA gene were chosen and specificity was verified by amplicon melting temperature. The method is sensitive enough to detect as low as 20 fg of M. leprae DNA, equivalent to four bacilli. The assay showed 100% concordance with clinical diagnosis in cases of multibacillary patients, and 50% of paucibacillary leprosy. The entire procedure of DNA extraction and PCR could be performed in c. 3 h. According to normalized quantitative real-time PCR, the patients in this study had bacilli numbers in the range of 1.07 x 10(2) -1.65 x 10(8) per 6-mm3 skin biopsy specimen. This simple real-time PCR assay is a facile tool with possible applications for rapid detection and simultaneous quantification of leprosy bacilli in clinical samples.

Tuberculin skin test and QuantiFERON-TB Gold In-tube Test for latent tuberculosis in Thai HIV-infected adults

Limited data exist for the performance of QuantiFERON‐TB Gold In‐tube Test (QFT‐IT) in comparison to tuberculin skin test (TST) for detecting latent tuberculosis (LTB) in patients with human immunodeficiency virus (HIV) infection from tuberculosis (TB)‐endemic Asia‐Pacific countries.

QuantiFERON®-TB Gold In-tube Test for tuberculosis prevention in HIV-infected patients

Optimal testing strategies for diagnosing latent tuberculosis infection and the administration of isoniazid preventive therapy (IPT) remain uncertain among human immunodeficiency virus (HIV)-infected patients. A 4-year prospective study was conducted among Thai HIV-infected patients who underwent simultaneous tuberculin skin test (TST) and QuantiFERON-TB Gold In-Tube Test (QFT-IT) at care entry. Based on baseline test results, patients were categorized into the following 4 groups: i) QFT-IT-positive, TST-reactive; ii) QFT-IT-positive, TST-non-reactive; iii) QFT-IT-negative, TST-reactive; and iv) QFT-IT-negative, TST-non-reactive. The QFT-IT-positive patients were offered 9-month IPT and were QFT-IT tested annually. Of the 150 enrolled patients, 8, 12, 16, and 114 patients were assigned to groups 1, 2, 3, and 4, respectively. Sixteen of 19 QFT-IT-positive patients (84%) completed IPT. The incidence of tuberculosis was significantly higher in patients who declined IPT than in those underwent treatment (11.11 vs. 0 case/100 patient-year; P ＜ 0.001). Among the 16 patients completing IPT, 11 (69%) and 2 (12%) had QFT-IT reversion at 1 and 2 years after IPT, respectively. The remaining 3 (19%) did not demonstrate any reversion, and their baseline interferon-γ (IFN-γ) levels were above 1.2 IU/mL. Initial QFT-IT-guided IPT was effective in preventing tuberculosis. Serial QFT-IT for evaluating IPT effectiveness had limitations because of delayed or lack of reversion, especially for patients with high baseline IFN-γ levels.

Tuberculin skin test and QuantiFERON®-TB Gold In-tube Test for diagnosing latent tuberculosis infection among Thai healthcare workers

A cross-sectional study was conducted on the performance of the tuberculin skin test (TST) and QuantiFERON(®)-TB Gold In-Tube test (QFT-IT) for detecting latent tuberculosis infection among Thai healthcare workers (HCWs). Each HCW underwent both the TST and QFT-IT during the annual health screening. Among the 260 HCWs enrolled, the median age was 30 years (range 19-60 years), 92% were women, 64% were nurses and nurse assistants, 78% were Bacillus Calmette Guérin vaccinated, and 37% had previously taken the TST. Correlation between TST reaction size and the interferon-γ level was weak (r = 0.29; P < 0.001). Of the HCWs, 38% and 20% had a reactive TST and a positive QFT-IT, respectively. Using QFT-IT positivity as a standard for latent tuberculosis diagnosis, the cut-off for TST reactivity with the best performance was ≥13 mm with a sensitivity, specificity, false positivity, and false negativity of 71%, 70%, 30%, and 29%, respectively (area under the curve 0.73; P < 0.001). The independent factor associated with a false reactive TST was a previous TST (adjusted odds ratio 1.83; P = 0.04). Our findings suggest that the QFT-IT may be the preferred test among HCWs with previous TST. In settings where the QFT-IT is not available, appropriate cut-offs for TST reactivity should be evaluated for use among HCWs.