Effect of Xpert MTB/RIF on detection of rifampicin resistance under different bacterial loads
10.11816/cn.ni.2025-246913
- VernacularTitle:不同菌量负荷下Xpert MTB/RIF检测利福平耐药的效果评价
- Author:
Yuehong HU
1
;
Qingmei YANG
;
Bingxu HUANG
Author Information
1. 厦门大学附属第一医院肺科,福建厦门 361022
- Publication Type:Journal Article
- Keywords:
Mycobacterium tuberculosis;
Xpert MTB/RIF;
Rifampicin resistance;
Bacterial load
- From:
Chinese Journal of Nosocomiology
2025;35(12):1775-1780
- CountryChina
- Language:Chinese
-
Abstract:
OBJECTIVE To analyze the reliability of Xpert MTB/RIF(referred to as Xpert)in detecting rifampicin resistance under varying bacterial loads of Mycobacterium tuberculosis(MTB)so as to reference for clinical diag-nosis and treatment.METHODS A total of 3 050 mycobacterial culture-positive test results from Jan.2016 to Dec.2023 at the First Affiliated Hospital of Xiamen University were selected.After excluding 220 non-tubercu-lous mycobacteria cases,2 830 culture-positive specimens underwent Xpert testing,with 2 412 positive and 418 negative cases.Based on MTB bacterial load,specimens were divided into four treatment groups-high,medi-um,low and very low-with 552,916,656 and 288 cases,respectively.Solid phenotypic drug susceptibility testing(DST)was performed on 1 801 MTB strains that were both culture-positive and Xpert-positive.RESULTS The positive rates of rifampicin in the high,medium,low and very-low treatment groups were 10.33％(57/552),11.14％(102/916),8.54％(56/656)and 8.68％(25/288),respectively.Using the solid phenotypic drug sus-ceptibility testing results as the reference standard,the specificity and negative predictive value of Xpert for detec-ting rifampicin resistance in all four bacterial load groups exceeded 96％,with no statistically significant differ-ences observed.No significant difference in sensitivity was noted among the groups(P=0.053),though the high bacterial load group exhibited relatively lower sensitivity at 84.62％(44/52),while the very-low bacterial load group showed the lowest sensitivity at 76.00％(19/25),which was lower than the medium bacterial load group's 94.05％(79/84).The positive predictive values(PPV)across all groups were generally low but without statisti-cally significant differences(P=0.239),with the high and very-low bacterial load groups registering PPVs of 77.19％(44/57)and 76.00％(19/25),respectively.The concordance rates of Xpert and solid phenotypic drug susceptibility testing were consistently high among all four bacterial load groups,including 94.95％(395/416),97.51％(666/683),96.75％(477/493)and 94.26％(197/209),respectively,with no significant difference(P=0.052).The Kappa values from high to very-low bacterial load groups were 0.778,0.889,0.831 and 0.727,re-spectively.Among the strains with discordant results between Xpert and phenotypic drug susceptibility testing,the rifampicin result consistency rates between Xpert and gene chip were 81.82％(9/11),100.00％(9/9),100.00％(2/2)and 25.00％(1/4),respectively for the high to very-low bacterial load groups.CONCLUSIONS When the bacterial load of MTB is very low,the Xpert assay demonstrates a higher probability of both false-posi-tive and false-negative results for rifampicin resistance,followed by high bacterial loads.The most reliable detec-tion of rifampicin resistance occurs with medium bacterial loads.
