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Prospective study to find out the role of gastric aspirate examination by Ziehl-Neelsen staining (ZN staining) and cartridge based nucleic acid amplification test (CB-NAAT) as a diagnostic method in childhood tuberculosis

World Health Organization (WHO) estimated the global burden of tuberculosis (TB) at 9 million new cases and 1.5 million deaths in 2013. This included upto 15% burden of paediatric cases. About 74000 children die of TB every year and there are around half a million new cases annually. Tuberculosis in children has been relatively neglected, mainly due to challenges in the availability of effective diagnostic tools. India is 17 among 22 high burden countries in terms of overall TB incidence rate. In most settings the diagnosis in children is traditionally based on the basis of contact tracing and very few attempts have been made for active case detection. This is mainly due to lack of pathognomic clinical presentation in paediatric Tuberculosis and lack of sensitive diagnostic tools. Microbiological confirmation with identification of drug resistance is ABSTRACT


INTRODUCTION
World Health Organization (WHO) estimated the global burden of tuberculosis (TB) at 9 million new cases and 1.5 million deaths in 2013. 1 This included upto 15% burden of paediatric cases. About 74000 children die of TB every year and there are around half a million new cases annually. 2 Tuberculosis in children has been relatively neglected, mainly due to challenges in the availability of effective diagnostic tools. 3 India is 17 th among 22 high burden countries in terms of overall TB incidence rate. 4 In most settings the diagnosis in children is traditionally based on the basis of contact tracing and very few attempts have been made for active case detection. This is mainly due to lack of pathognomic clinical presentation in paediatric Tuberculosis and lack of sensitive diagnostic tools. [3][4][5][6] Microbiological confirmation with identification of drug resistance is increasingly important in the context of an emerging drug resistant tuberculosis epidemic. Infants and young children do not expectorate but instead swallow their sputum. Aspiration or lavage of gastric content is best procedure in them for obtaining specimen from which to culture Mycobacterium tuberculosis. Cartridge based nucleic acid amplification test is a nucleic acid amplification test which simultaneously detects DNA of Mycobacterium tuberculosis complex (MTBC) and resistance to rifampicin (RIF) in less than 2 hours. This system integrates and automates sample processing, nucleic acid amplification and detection of the target sequences.
Therefore, authors have conducted a study on role of gastric aspirate in detection of acid fast bacilli by Ziehl-Neelsen stain and Cartridge based nucleic acid amplification test in the diagnosis of childhood Tuberculosis.

METHODS
The study was a prospective hospital-based study conducted from November 2016 to November 2017 in the Department of Paediatrics, JLN Medical College and Associated group of Hospitals, Ajmer. Study group comprised of 100 randomly selected patients <=12 years of age of either sex who met the following criteria.

Patient with clinical/investigational suspicion of tuberculosis who met any of the following
• Fever and or cough for > 2 weeks • History of weight loss or no weight gain in past 3 months (loss of weight defined as loss of more than 5% body weight as compared to highest weight recorded in last 3 months) • Hilar lymphadenopathy on chest skiagram • Tuberculin skin test positivity • Coexistence of precipitating illness • Abdominal USG suggestive of tuberculosis • ADA positivity in pleural fluid • CSF findings consistent with tubercular meningitis • Cranial CT suggestive of tuberculoma.

Patient who has not taken anti tuberculosis drugs.
All the selected patients were subjected to detailed history, general physical examination, systemic examination, haematological investigations, tuberculin sensitivity test and gastric aspiration for Ziehl-Neelsen staining and cartridge based nucleic acid amplification test. Other relevant Investigations were done where ever necessary to support the diagnosis.
The sensitivity, specificity, positive predictive value and negative predictive value were calculated for both cartridge based nucleic acid amplification test and Ziehl-Neelsen staining using culture as the gold standard. Chi square test was used to correlate the various findings with the test results.

RESULTS
Majority of the cases included in present study were in the age group of 0-5 years (57%) followed by age group of 5-12 years and least were 10-12 years (16%). 55% males and 45% females were included in this study. Maximum no. of cases was of lower middle class (class III) with 42% and upper lower (class IV) with 23% according to kuppuswamy scale for socioeconomic status. Progressive pulmonary tuberculosis was the most common type of tuberculosis included in this study. Fever, cough of more than 2 weeks, weight loss/no weight gain and anorexia were the most common presenting complaints.
The sensitivity, specificity, positive predictive value and negative predictive value of Ziehl-Neelsen staining for acid fast bacilli were 47.6%, 98.7%, 90.9% and 87.6% respectively as compared to culture as gold standard. The sensitivity, specificity, positive predictive value and negative predictive value of Cartridge based nucleic acid amplification test were 76.1%, 98.7%, 94.1% and 93.9% respectively. There was no association for absence of BCG scar and positivity of Cartridge based nucleic acid amplification test. Statistical significance was recorded for positive Cartridge based nucleic acid amplification test and presence of history of contact with tuberculosis.
There was a positive association found between reactivity of Mantoux test and positive Cartridge based nucleic acid amplification test result. Cartridge based nucleic acid amplification test was found positive maximum in class III and class IV socioeconomic groups according to kuppuswamy classification. Statistical significance was recorded for positive Ziehl-Neelsen staining and presence of history of contact with tuberculosis There was a positive association found between reactivity of Mantoux test and positive Ziehl-Neelsen stain for acid fast bacilli.    Table 3 shows percentage of children in present study with positive history of contact were 33% while 67% had no history of contact rpoB gene was detected by cartridge based nucleic acid amplification test in 41.1% cases with absent history of contact and 58.8% cases with positive history of contact with a p-value of 0.0217 which is statistically significant.
In Table 4, the sensitivity, specificity, positive predictive value and negative predictive value for Ziehl-Neelsen staining were 47.6%, 98.7%,90.9% and 87.6% respectively taking culture as the gold standard.   Detjen AK et al showed that compared with culture, the pooled sensitivity and specificity of Xpert for tuberculosis detection were 66% and 98% respectively with use of samples from gastric lavage. Xpert sensitivity was 36-44% higher than was sensitivity for microscopy. 8 Pang et al got a sensitivity of 48.6% and concluded that Xpert is an excellent tool for the diagnosis of smear negative tuberculosis with gastric lavage samples while Singh et al concluded the sensitivity of 62.5% in smear negative and culture positive samples with both gastric lavage and induced sputum samples. 9,10 Authors report positive rate of Cartridge based nucleic acid amplification test in patients with history of tuberculosis contact was significantly higher (p value 0.0217) than that with no history of contact. Also, the positivity of Cartridge based nucleic acid amplification test was higher in lower socioeconomic groups (class III and IV

CONCLUSION
Authors can safely conclude that Cartridge based nucleic acid amplification test on one gastric aspirate sample rapidly and correctly identified the majority of children with culture confirmed tuberculosis with a high specificity.
Positive history of contact, reactive tuberculin sensitivity test and low socioeconomic status were independently associated with a positive Cartridge based nucleic acid amplification test result.
This test is widely anticipated to replace smear microscopy in resource-poor settings where HIV coinfection or drug-resistant tuberculosis are common, and present results suggest that its use is a major improvement over use of smear microscopy. Although time to detection was not a primary outcome for this study, cartridge based nucleic acid amplification test results were available within 1 day, which was substantially faster than for culture results.
Cartridge based nucleic acid amplification test performs well in Gastric aspirate samples for rapid and accurate diagnosis of childhood tuberculosis; the assay is more sensitive than smear microscopy for the diagnosis of childhood tuberculosis with gastric aspirate samples; and the assay detected an extra 6 cases of tuberculosis compared with smear microscopy.
Present study was done in a single, tertiary referral centre with high tuberculosis burden; therefore, it cannot be assumed that the accuracy of the cartridge based nucleic acid amplification test for the detection of childhood pulmonary tuberculosis will be the same in other patient cohorts or settings.
Acid-fast smear of gastric aspirate is a highly specific test for the diagnosis of PTB in children. A positive acid-fast smear should warrant commencement of the full course of anti-TB therapy.