[Experimental study of GeneXpert(®) system in the diagnosis of extra-pulmonary tuberculosis].

OBJECTIVE

To explore the application value of GeneXpert MTB/RIF for detection of extra-pulmonary tuberculosis and resistance to rifampin.

METHODS

A total of 150 samples were collected, including 33 needle aspirates from lymphoid tuberculosis, 23 needle aspirates from spinal tuberculosis, 49 from tuberculous pleural effusions, 24 from cerebrospinal fluid of tuberculous cephalomeningitis, and 21 urinary sediment samples from renal tuberculosis. Smear microscopy, mycobacterium tuberculosis culture and the MTB/RIF method were used to examine these samples and their positive rates were compared. Rifampin susceptibility tests was performed for culture-positive strains using proportion method, which was compared with the result from GeneXpert MTB/RIF method.

RESULTS

Of the 150 cases of extra-pulmonary tuberculosis, 17 samples were smear-positive, with a sensitivity of 11.3% (17/150); 30 were culture-positive with a sensitivity of 20.0% (30/150); and 96 were positive by MTB/RIF method with a sensitivity of 64.0% (96/150). There was a significant difference between MTB/RIF method and the culture method (χ(2)=59.61, P<0.01). The differences were also significant when the MTB/RIF method was compared with the smear method (χ(2)=88.60, P<0.01) or compared with culture plus smear methods (χ(2)=4.26, P<0.05). Separately, the differences were statistically significant between GeneXpert MTB/RIF method and other 2 methods for diagnosis of lymphoid tuberculosis (n=33, χ(2)=20.56, P<0.01 vs. culture method; χ(2)=27.13, P<0.01 vs. smear results) while no difference was found between culture and smear method (χ(2)=0.67, P>0.05), spinal tuberculosis (n=23, χ(2)=12.74, P<0.01 vs. culture method; χ(2)=14.81, P< 0.01 vs. smear method), tuberculous pleurisy (n=49, χ(2)=32.34, P<0.01 vs.culture method; χ(2)=49.69, P<0.01 vs. smear method) and renal tuberculosis (n=21, χ(2)=4.20, P<0.05 vs. culture method; χ(2) =8.40, P<0.01 vs. smear results). The sensitivity for tuberculous meningitis had no difference among these 3 methods (n=24, P>0.05). Rifampicin-resistance of the strains from the 30 culture-positive cases of extra-pulmonary tuberculosis (20.0%, 6/30) exhibited agreement with GeneXpert MTB/RIF test.

CONCLUSION

The simplicity and high sensitivity of GeneXpert MTB/RIF technology make it a good diagnostic test for rapid detection of extra-pulmonary tuberculosis and resistance to rifampin.