MYCOBACTERIUM TUBERCULOSIS KOMPLEKSİNİN VARLIĞININ SAPTANMASINDA VE RİFAMPİSİNE DİRENCİNİN BELİRLENMESİNDE XPERT MTB/RIF TESTİNİN DEĞERLENDİRİLMESİ

Tüberküloz hala tüm dünyada önemli bir sağlık sorundur. Mycobacterium tuberculosis’in varlığının ve ilaç direncinin hızlı bir şekilde belirlenmesinde günümüzde moleküler yöntemler artan sıklıkta kullanılmaktadır. Bu çalışmada M.tuberculosis kompleksinin (MTBC) doğrudan klinik örnekten tanısında ve rifampisine (RIF) direncinin belirlenmesinde Xpert MTB/RIF testi değerlendirilmiş, sonuçlar referans yöntem olarak Löwenstein-Jensen (L-J) ve Bactec MGIT 960 sistemi ile karşılaştırılmıştır. Bu amaçla 1022’si solunum yolu ve 700’ü solunum yolu dışı olmak üzere toplam 1722 örnek incelenmiştir. İncelenen solunum yolu örneklerinin 119’u (% 11.6) hem kültür hem de Xpert MTB/ RIF testi ile pozitif olarak bulunmuştur. Bu örneklerin 76’sının (% 7.4) preparatı aside dirençli bakteri (ARB) negatif, 43’ünün (% 4.2) pozitif sonuç vermiştir. Çalışmaya dahil edilen solunum yolu dışı örneklerinin ise 24’ünün (% 3.4) hem kültür, hem de Xpert MTB/RIF testi sonucu pozitiftir. Ehrlich Ziehl Neelsen (EZN) boyama yöntemiyle bu örneklerin 18’i (% 2.6) ARB negatif, altısı (% 0.9) pozitif bulunmuştur. Xpert MTB/RIF testinin solunum yolu örneklerinde duyarlılık, özgüllük, pozitif ve negatif prediktif değerleri sırasıyla % 97.5, % 99.8, % 98.3 ve % 99.7 olarak, solunum yolu dışı örneklerinde ise % 82.8, % 99.6, % 88.9 ve % 99.3 olarak belirlenmiştir. ARB pozitif solunum yolu örneklerinde duyarlılık % 100 iken, özgüllük değeri hesaplanamamıştır. ARB negatif solunum yolu örneklerinde ise duyarlılık ve özgüllük % 96.2 ve % 99.8 olarak belirlenmiştir. ARB pozitif solunum yolu dışı örneklerde duyarlılık % 100 olarak belirlenmiş, özgüllük ise hesaplanamamıştır. ARB negatif solunum yolu dışı örneklerde ise duyarlılık ve özgüllük % 78.3 ve % 99.6 olarak saptanmıştır. Tüm örnekler birlikte değerlendirildiğinde ARB pozitif örneklerde duyarlılık % 100 olarak belirlenmiş, özgüllük ise hesaplanamamıştır. ARB negatif örneklerde ise duyarlılık ve özgüllük % 92.2 ve % 99.7 olarak belirlenmiştir. Örneklerin toplam olarak 143’ünde (% 8.3) hem kültür, hem de Xpert MTB/RIF testi ile pozitif sonuç elde edilmiştir. Xpert MTB/RIF testi ile bu suşların 128’inin (% 89.5) RIF’e duyarlı, 15’inin (% 10.5) dirençli olduğu belirlenmiştir. Xpert MTB/RIF testi, MGIT 960 yöntemiyle yapılan ilaç duyarlılık testi (İDT) ile % 100 uyumlu sonuç vermiştir. Sonuç olarak, Xpert MTB/RIF testi hem solunum yolu, hem de solunum yolu dışı örneklerde MTBC varlığının belirlenmesinde duyarlılığı ve özgüllüğü yüksek, hızlı ve kolay uygulanabilir bir yöntem olarak belirlenmiştir. Ancak bu test ile RIF’e dirençli olduğu belirlenen M. tuberculosis suşlarının sonuçlarının konvansiyonel İDT ile tekrarlanmasının doğru olacağı düşünülmüştür.

Evaluation of Xpert MTB/RIF Assay for Direct Detection of Mycobacterium tuberculosis Complex and Rifampicin Resistance

Tuberculosis is still a major health problem all over the world. Nowadays molecular methods are increasingly being used for rapid detection of M.tuberculosis and the drug resistance. In this study, the Xpert MTB/RIF test was evaluated for direct detection of M.tuberculosis complex (MTBC) and rifampicin (RIF) resistance, and the results were compared with Löwenstein Jensen (L-J) and Bactec MGIT 960 system as reference methods. For this purpose, totally 1722 specimens were examined, including 1022 respiratory and 700 non-respiratory. Among respiratory specimens, 119 (11.6%) were positive both by culture and by the Xpert MTB/RIF test. Of these specimens, 76 (7.4%) smears were acid fast bacilli (AFB) negative and 43 (4.2%) were positive. Of the non-respiratory specimens included in the study, 24 (3.4%) were positive both by culture and the Xpert MTB/RIF test. The smear of 18 of these specimens (2.6%) were AFB negative while six (0.9%) were positive. The sensitivity, specificity, positive and negative predictive values of the Xpert MTB/RIF test in respiratory specimens were 97.5%, 99.8%, 98.3% and 99.7%, respectively, and in non-respiratory specimens were 82.8%, 99.6 %, 88.9 % and 99.3%. Sensitivity was detected as 100% in AFB positive respiratory specimens, but specificity could not be calculated. Sensitivity and specificity were calculated as 96.2% and 99.8% in AFB negative respiratory specimens. Sensitivity was determined as 100 % for AFB positive non-respiratory specimens while specificity could not be calculated. Sensitivity and specificity were determined as 78.3% and 99.6% for AFB negative non-respiratory specimens. When all specimens were evaluated together, the sensitivity was determined as 100 % for AFB positive ones and the specificity could not be calculated. Sensitivity and specificity were 92.2 % and 99.7% for AFB negative specimens. Totally 143 specimens (8.3%) were positive both by culture and the Xpert MTB/RIF test. It was determined that 128 (89.5%) of these strains were sensitive and 15 (10.5%) were resistant to RIF by the Xpert MTB/RIF test. The Xpert MTB/RIF test was 100% compatible with the MGIT 960 drug sensitivity test (DST). In conclusion, the Xpert MTB/RIF test has been identified as a rapid, easily applicable method with high sensitivity and specificity for direct detection of MTBC in both respiratory and non-respiratory specimens. However, it was concluded that it would be right to confirm RIF resistant M.tuberculosis strains by conventional DST.

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