|Year : 2020 | Volume
| Issue : 3 | Page : 327-331
The use of GeneXpert Mycobacterium tuberculosis/rifampicin assay in diagnosis of pulmonary tuberculosis in children
Mohammed S Abdelwahab, Fardous H Abdel-Aal, Shereen M Galal
Department of Pediatrics, Faculty of Medicine, Assiut University, Assiut, Egypt
|Date of Submission||25-Feb-2020|
|Date of Decision||30-Mar-2020|
|Date of Acceptance||04-May-2020|
|Date of Web Publication||10-Aug-2020|
Mohammed S Abdelwahab
Department of Pediatrics, Faculty of Medicine, Assiut University, Assiut
Source of Support: None, Conflict of Interest: None
Rapid diagno sis of tuberculosis (TB) is essential for early disease management. GeneXpert (GX) test is a novel rapid diagnostic modality. In this study, we aimed to evaluate the diagnostic role of GX test in diagnosing pulmonary tuberculosis (PTB) in children as well as detection of rifampicin (RIF) resistance.
Patients and methods
This was a cross-sectional study that included 80 patients suspected to have PTB based on clinical data together with at least one of the followings: a positive tuberculin skin test or QuantiFERON-TB Gold In-Tube test result, a positive blood TB PCR result, or a positive Ziehl–Neelsen staining result.
PTB was more common in older females. Extrapulmonary manifestations and hilar lymphadenopathy were more frequent in younger age. Both positive tuberculin skin test and positive GX were more frequent in older age. Positive GX was found in 30 (37.5%) cases, and RIF resistance was detected in two (6.6%) of them. Positive GX results were more frequent in sputum than gastric aspirate samples. Positive GX results were more frequent with absent Bacillus Calmette–Guérin scar, and with hemoptysis, failure to thrive, cavitary lung lesions, and lower mean hemoglobin.
GX detects many more cases than blood PCR and Ziehl–Neelsen stain. GX had 70% sensitivity and 95% specificity in diagnosing PTB, with overall diagnostic accuracy of 86.67%, with better performance in older children who could expectorate. RIF resistance was ∼6.6%.
Keywords: blood PCR, GeneXpert, pediatric, pulmonary tuberculosis
|How to cite this article:|
Abdelwahab MS, Abdel-Aal FH, Galal SM. The use of GeneXpert Mycobacterium tuberculosis/rifampicin assay in diagnosis of pulmonary tuberculosis in children. J Curr Med Res Pract 2020;5:327-31
|How to cite this URL:|
Abdelwahab MS, Abdel-Aal FH, Galal SM. The use of GeneXpert Mycobacterium tuberculosis/rifampicin assay in diagnosis of pulmonary tuberculosis in children. J Curr Med Res Pract [serial online] 2020 [cited 2020 Sep 25];5:327-31. Available from: http://www.jcmrp.eg.net/text.asp?2020/5/3/327/291767
| Introduction|| |
Incidence of tuberculosis (TB) in Egypt was estimated to be 13 cases (per 100 000 population), which is the lowest in Africa and among the lowest in WHO Eastern Mediterranean region. However, the rising incidence of drug-resistant TB complicates the battle against TB .
Children younger than 5 years represent a special population regarding risk, presentation, and diagnosis of TB. Despite being the oldest among TB investigations, chest radiograph and tuberculin skin test (TST) still have a valuable role beside microbiologic confirmation, which was rarely attempted in children mainly owing to the incorrect perception that respiratory specimens are difficult or impossible to obtain in children. Moreover, even when samples were obtained, the yield of the organism was very low . The GeneXpert (GX) Mycobacterium tuberculosis (MTB)/rifampicin (RIF) assay represents a candidate solution for this problem. GX uses a real-time reverse transcription PCR technology using unprocessed clinical specimens, regardless of their smear status. GX probes for the rpoB gene of MTB, which encodes for most cases with RIF resistance. Thus, it can simultaneously identify the organism and RIF resistance, which is a strong indicator of concurrent multidrug resistant TB, within 2 h. GX uses molecular beacon technology to detect DNA sequences using five different nucleic acid hybridization probes in the same multiplex reaction. The assay is conducted within a simple, almost fully automated cartridge-based system .
| Aim|| |
The aim was to evaluate the diagnostic role of GX MTB/RIF assay in pulmonary tuberculosis (PTB) in children as well as detection of RIF resistance.
| Patients and Methods|| |
The study included 80 patients suspected to have PTB who attended to Assiut University Children Hospital from April 2017 to March 2019. Their ages ranged from 1 to 18 years. They comprised 35 males and 45 females. Patients were divided in our study into two groups:
Group 1: infants and children up to 5 years old (N = 23).
Group 2: children and adolescents up to 18 years old (N = 57).
All studied patients were subjected to thorough clinical evaluation, besides complete blood count, TST, and blood PCR assay for MTB. Respiratory samples [sputum/gastric aspirate (GA)] were obtained in the morning after overnight fasting and subjected to the following: (a) Ziehl–Neelsen (ZN) staining, following WHO guidelines ; (b) culture on Lowenstein–Jensen media was done for 30 (37.5%) cases only, following WHO guidelines ; and (c) GX assay, following WHO guidelines .
Patients suspected to have PTB based on clinical data, such as prolonged cough (>1 month) not responding to nonspecific treatment and TB toxemia (night fever, night sweating, anorexia, or weight loss), together with at least one of the followings were included:
- Positive TST or QuantiFERON-TB Gold In-Tube test.
- Positive blood TB PCR.
- Positive ZN smear for acid-fast bacilli.
The following were the inclusion criteria:
- Neonates and infants (<1 year).
- Children with chronic cough owing to other causes, such as bronchial asthma, interstitial pulmonary fibrosis, or cystic fibrosis.
- Patients suspected to have extrapulmonary TB (EPTB) only.
- Patients who have started anti-TB treatment.
- Human immunodeficiency virus-positive cases.
Continuous data were expressed in the form of mean ± SD (range), whereas categorical variables were described by frequencies [n (%)]. X2 test was used to compare between categorical variables, whereas Student t test was used to compare the means of groups. A two-tailed P value less than 0.05 was considered statistically significant. All analyses were performed with the IBM SPSS 20.0 software (IBM Corp., Armonk, New York, USA).
The study was approved and monitored by the Medical Ethics Committee, Assiut Faculty of Medicine, IRB No. 17100059. The investigators explained the steps and value of the research to the parents/guardians of all eligible participants. Those who agreed to participate signed a fully informed consent form.
The parameters to be assessed were as follows:
- Frequency of positive GX versus results of ZN stain, blood PCR, TST, and culture.
- Sensitivity and specificity of GX (with culture as reference standard).
- Frequency of RIF resistance as detected by GX.
| Results|| |
The number of patients older than 5 years was significantly higher than younger children. The number of female cases was higher in older age group, but no significant difference was noted regarding frequencies of symptoms or clinical diagnoses. Frequency of extrapulmonary manifestations was higher in younger age, and the commonest was cervical lymphadenopathy.
Radiologic and laboratory findings of our patients are detailed in [Table 1].
In cases with positive GX, RIF resistance was detected in two (6.6%) cases.
Regarding sample type in GX and ZN stain, in GX assay, 24 (48%) sputum samples were positive and six (20%) GA samples were positive, whereas in ZN stain, 15 (30%) sputum samples were positive and three (10%) GA samples were positive. The frequencies of positive GX and positive ZN stain were both higher in sputum than GA samples.
Frequency of positive GX was higher with older age, with absent Bacillus Calmette–Guérin (BCG) scar and with positive contact history. Frequency of positive GX results was higher with hemoptysis and with failure to thrive.
[Table 2] demonstrates the frequency of GX positivity versus different radiologic and laboratory findings.
|Table 2: Frequency of GeneXpert positivity in contrast with different radiologic and laboratory findings|
Click here to view
The most common radiologic finding in both positive and negative cases was hilar lymphadenopathy followed by consolidation. Frequency of positive GX was higher with cavitary lesions.
Regarding hematological parameters, patients with positive GX had lower hemoglobin levels.
In patients with negative culture, ZN examination was positive in one (5%) and negative in 19 (95%), but in those with positive cultures, ZN examination was positive in six (60%) and negative in four (40%). Based on culture results, GX had 70% sensitivity and 95% specificity in diagnosing PTB with overall diagnostic accuracy of 86.67%. On the contrary, ZN examination had 60% sensitivity and 95% specificity in diagnosing PTB, with overall diagnostic accuracy of 83.33%.
| Discussion|| |
TB was significantly higher in older group owing to increased exposure to infection and waned protection from BCG vaccine, which declines with time and can last for up to 10 years . Adolescents have many contacts and are at high-risk for contracting TB .
Moreover, the number of females was significantly higher in older group (63.3%) than younger group (39%). This agrees with Margarit et al. . Women nowadays socialize as men do, but their gatherings are often in confined spaces, unlike males.
We found that the associating extrapulmonary manifestations were more frequent in younger age. Feja and Saiman attributed this observation to immunologic host factors. However, Cano et al. reported that age did not influence disease presentation as PTB or EPTB.
We found hilar lymphadenopathy as the most common radiographic finding (82.5%). Hilar lymphadenopathy was more frequent in young age. This agrees with Boloursaz et al. . This can be explained by the nature of disease process of TB.
TST was positive in most patients (73.75%), and TST positivity was more frequent in older group. This agrees with Beshir et al. . Cano et al. reported similar frequency of TST positive cases (72.3%); however, such frequency was slightly higher in younger age.
PCR was positive in 18.75% of our patients, with no significant difference with age. This is consistent with Lima et al. . There is scarcity of studies about blood PCR in pediatric PTB.
ZN stain was positive in our 18 (22.5%) patients. This can be explained by the paucibacillary nature of TB in children. However, other studies reported variable results ,. Jain et al. reported that microbiological positivity was associated with higher mean age.
Regarding GX results, 30 (37.5%) patients were positive, with significantly higher frequency in older children. This is comparable to Kasa et al. . Several studies showed variation in frequency of positive cases above or below our figures, mainly owing to variation in inclusion and exclusion criteria.
Our study showed that GX positivity was more frequent in older group. This agrees with Sekadde et al. and Detjen et al. . However, Yin et al. reported contradicting results.
In positive GX cases, we found RIF resistance in two (6.6%) patients: one (3.7%) among new TB cases and one (33.3%) among previously treated cases. This agrees with the latest Egyptian Drug Resistance Survey in 2010 .
Regarding sample type, both GX and ZN stain had better performance in sputum samples. There is evidence that supports that GA has inferior yield compared with other respiratory samples in diagnosing PTB, such as Hepple et al. and Singh and Tiwari .
A much larger bulk of evidence, however, supports the reliability of GA in diagnosing PTB, such as Pang et al. and Detjen et al. . The latter reported that the pooled sensitivity and specificity of GX for TB detection were 62 and 98%, respectively, with the use of sputum, and 66 and 98%, respectively, with the use of GA. GX sensitivity was 40% higher than microscopy .
GX was significantly more frequently positive in those with absent BCG scar. This agrees with Yin et al. and Jain et al. . This can be explained by BCG-induced immunity enhances containment of TB organisms, preventing their appearance in respiratory samples.
GX was significantly more frequently positive in those with contact history of TB. This agrees with Sekadde et al. and Yin et al. . However, contact history is a risk factor for TB in both microbiologically positive and negative patients .
Positive GX was more frequent in those with hemoptysis. Campos et al. reported that hemoptysis was less frequent in smear-negative patients as hemoptysis is associated with cavitation, which is associated with more bacillary yield.
Positive GX was more frequent in those with failure to thrive, as weight loss is a consequence of severity and/or long duration of TB illness. Both of which were found to predict high bacteriologic yield . Jain et al. reported that low BMI was associated with microbiological confirmation in children with PTB.
Cavitary lesions were significantly more common in those with positive GX results. Palaci et al. reported that patients with cavitary disease had higher colony forming unit levels.
Patients with positive GX had significantly lower hemoglobin levels. This agrees with Kerkhoff et al. and Jain et al. . Lower hemoglobin may reflect severity and/or duration of TB illness.
TST was much more frequently positive than GX without significant association between them. This agrees with Hanrahan et al. . However, Sekadde et al. reported that a positive TST was associated with a positive GX test.
Positive GX was more frequent in those with positive blood PCR. As we address PTB, it is expected that respiratory samples to be of more yield than blood samples. Lima et al. reported that the sensitivity of blood PCR was higher for EPTB (55.56%) than PTB (18.18%).
GX could confirm much more cases than ZN smear. This agrees with Dzodanu et al. and others. GX requires smaller number of organisms for detection than acid-fast bacilli staining .
| Conclusion|| |
In conclusion, GX detected much more cases than blood PCR and ZN stain. GX had 70% sensitivity and 95% specificity in diagnosing PTB with overall diagnostic accuracy of 86.67% (with culture as gold standard), with better performance in older children who could expectorate. RIF resistance rate was 6.6%.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]