New Interferon-γ Release Assay in Microbiological TB Investigation for CNS Tuberculosis

1. Introduction of the New Interferon-γ Release Assay in the Microbiological TB Investigation Protocol for Central Nervous System Tuberculosis in Children: A Modern Tool versus an Old Plague BAMBINO GESU’ Children Hospital HealthCare and Research Institute Rome - ITALY russocri@opbg.net C. Russo, L. Coltella, and D. Menichella - "Bambino Gesù" Children Hospital Health Care and Research Institute Abstract (revised) Background and Rationale of the Study Results and Discussion Central nervous system Tuberculosis (CNS-TB) is the most severe form of TB and frequently, is revealed as meningitis TB infection. Difficulties and technical hitches to obtain enough and satisfactory samples helpful for a microbiological TB diagnosis purpose are well known. We try to understand if and how the new Interefron-γ release assay QuantiFeron TB Gold (Cellestis Limited-Australia), is able to upgrade our microbiological diagnostic protocol. Methods: During the last three years (2004-2007) we investigated at Bambino Gesù Children Hospital in Rome, a total of eight cases clinical suspected as TB meningitis. For each one we applied the microbiological TB investigation protocol on Cerebrospinal fluid (CSF) and respiratory specimens composed by: Acid fast bacilli staining (AFB), cultures growth in liquid and solid media and nucleic acid amplification assay (NAA). In adjunction we performed on whole blood sample the QFT-G (liquid antigen and In tube version). Results : 4 out of 10 patients resulted negative for microbiological TB investigation protocol and received, a clinical diagnosis other than TB. About the other four patients (median age 3 ys): in three cases CSF resulted negative for AFB and NAA was not performed because insufficient; QFT-G was positive in three case at the first evaluation (Time 0) and in two cases showed a conversion of T-cell response: from Indeterminate to Positive and from Negative to Positive at a second assay performed into a new collectected blood sample. All these four TB cases were cultures confirmed. Tuberculin Skin Test was performed in all 10 patients and resulted as Negative. Discussion and Conclusion: As all guidelines recommend, is mandatory to use a correct microbiological approach to avoid to lack TB diagnosis. Our on field experience confirmed how is difficult to obtain the right amount and more than one sample of CNF in children. On the other hand, the introduction of a new not invasive sample collection (peripheral whole blood) and an easy to perform ELISA test able to investigate a T cell specific response against TB, could be considerate a valid and rapid tool to support the microbiological TB investigation protocol. The clinical presentation of TB in children is extremely variable. It depends by different factors as: the age, the immunocapability of the host response and also the TB spread. In particular Tuberculous meningitis (TBM) has high morbidity and mortality. Demonstration of tubercle bacilli in cerebrospinal fluid (CSF), the only reliable method of diagnosis, is time consuming and has a low yield. Also NAA commercial kits have low and varying sensitivities, and therefore should not be used for excluding a diagnosis of tuberculous meningitis. Moreover, cutaneous sensitivity to Purified Protein antigen Derivative (TST) is not satisfied. TB MENINGITIS Droplet infection • thick exudate developed by Rich foci rupture into the • subarachnoid space. The inflammatory response gives: • Adhesion (hydrocephalus) • Vasculitis (internal carotid stenosis) • Encephalitis (cerebral oedema) Primary pulmonary focus bacteraemia spread seeding of bacilli in meninges Tab 1 Surveillance of Tuberculosis in Europe Six children received the finaly diagnosis of TB meningitis In recent years, numerous authors studied possible biochemical markers such as interferon gamma (IFN- ), to improve diagnostic efficiency. Five out six children had foreign origin (four from Est Europe, one from Africa) The aims of our study have been: • to test if the new QuantiFeron TB Gold (QFT-G) is able to work in suspected TB meningitis as rapid tool for TB diagnosis. TST was not reactive (negative) in all children QFT-G was positive during the first evaluation for three children under 2 years of age Population and Methods INF- ELISA assay OUR PATIENTS Liquid andIn Tube version QuantiFeronTB-Gold Computed Tomography images showed hydrocephalus and basilar meningitis but with any evidence of tuberculoma From 2004 to 2007 we investigated children admitted Our study was carried out prospectively in a clinical routinely situation during the last three years. We assessed whether the new Interferon-γ release assay QuantiFERON-Gold could be used in practice in special setting (as pediatric population) and in extra-pulmonary localization as TB meningitis. • at “Bambino Gesù” Children Hospital (Rome, Italy) presenting with: • Signs or symtoms of meningitis compatible wich a TB suspected Step 1 samples collection Step 2 ELISA assay Step 3 Interpretation of INF-γ amount Mycobacterial Laboratory Investigation Protocol • Nucleid Acid Amplification • AFBfluorescence Stain • Solid and liquid media cultures Potential limitations of our study should be: the low number of cases may affect precision we did not evaluate children HIV affected (Cobas Amplicore®- Roche) Conclusions Tuberculosis (TB) is a systemic infection caused by Mycobacterium tuberculosis. It can produce disease in any organ system by haematogenous spread, specially in newborn and children. TB meningitis is the most severe form of TBanditmay be suspected on the basis of clinical or radiology experience. A correct diagnosis depends on the possibility to have a refererence mycobacteriology laboratory procedures for appropriate investigation. Specimens for cultures often requiring invasive procedures and sophisticated laboratory techniques and they are Time consuming. Our results reveal that: in case of suspected TB meningitis the QFT-G assay may offers rapid results expecially in children under 2 ys of age.In conclusion, in our experience QFT-G has revealed as a powerful tool to apply in a Mycobacterial laboratory investigation protocol for diagnosis of suspected TB meningitis in children. Presentation Number:U-008 Poster Board Number:0993 Acknowledgements Silvia Gobbi and Eugenia Galeno laboratory technicians Microbiology Unit – Laboratory Department Stefania Colafati MD for supporting in CT images and interpretation - Radiology Department