The Origin of Swine Flu

Transcription

1 How the Heck Do You Diagnose Tuberculosis in Children, Anyway? Jeffrey R. Starke, M.D. Professor and Vice Chairman of Pediatrics Baylor College of Medicine Houston, Texas USA The Origin of Swine Flu MAIN POINTS All existing diagnostic tests for TB infection and disease in children have significant short-comings Given the sensitivity and specificity of existing tests, positive predictive values are much greater when risk is higher A variety of typical chest radiograph findings are found in childhood tuberculosis

2 Tuberculosis is a social disease with medical implications. Estimated TB incidence rates, 2000 Rate per or more No estimate The boundaries and names shown and the designations used on this map do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines for which there may not yet be full agreement. Global Tuberculosis Control. WHO Report WHO/CDS/TB/ A Difficult Case A 7 yo HIV + girl has cough, abdominal pain, cervical and axillary adenopathy, bilateral rales and a large liver. A 10 day course of clarithromycin did not improve her symptoms. Her CD4 count was 291/20%, her hemoglobin was 8.9, but other labs were WNL. After several weeks, her cough improved, she was sweating a lot but did not have fever or weight loss. Her adult cousin had pulmonary tuberculosis 2-3 years ago [household contact]. Does she have tuberculosis?

3 DIAGNOSIS OF TUBERCULOSIS All existing diagnostic tests for TB in children have significant shortcomings Most tests are not available in settings where the vast majority of TB cases are diagnosed The utility of most tests is further diminished in children with immune compromise [especially HIV infection] DIAGNOSTIC TESTS FOR CHILDHOOD TUBERCULOSIS The sensitivity and specificity of the available tests are inherent in the tests However, the positive and negative predictive values are inherent in the population on whom the tests are used Therefore, all tests are more accurate when used on children with a high index of suspicion [epidemiology HISTORY OF RECENT CONTACT TO A TB CASE -or suspicious symptoms]

4 Sensitivity = Specificity = 95% 90% prevalence 1% prevalence PPV= 99% (1% false+) PPV=15% (85% false+) TRANSITIONS IN TUBERCULOSIS Susceptible Exposed *Infected Diseased Sick Diagnosed Treated Cured MANTOUX TUBERCULIN SKIN TEST uses 5 TU [2 TU if R23] of purified protein derivative interpret in hours record size of induration in mm if it makes a reaction at >72 hrs, it counts! false negatives: 10% to 20% in disease

5 FACTORS THAT CAUSE DECREASED RESPONSE TO TUBERCULIN Host-related Infections, vaccines Chronic disease, malnutrition Immunosuppressive diseases (HIV, malignancy, CVD) Drugs (corticosteroids) Extremes of age, stress Overwhelming tuberculosis Tuberculin - related Improper storage or dilution Adsorption to glass or plastic Administration - related Reading - related INDURATION SIZE POSITIVE TUBERCULIN SKIN TEST > 5 mm > 10 mm HIV co-infection Immune compromise Recent contact to TB Suspected disease > 15 mm No risk factors Previous BCG vaccination? Foreign-born from a HR country Drug users Living in HR congregate setting Specific HR groups Children < 4 yrs old (AAP)

6 INTERACTION OF BCG VACCINES WITH THE TUBERCULIN SKIN TEST 50% of vaccinated infants do not react to a TST; most of the rest stop reacting within 5 years most non-infants who get one or more BCG vaccinations will react to a TST (usually < 15 mm), but effect wanes over 5 10 years Current Dogma: outside infancy, positive TST more likely to indicate infection with M. tuberculosis than be residual from BCG TUBERCULIN SKIN TESTING OF FOREIGN-BORN ADOPTEES On one hand, most children have received a BCG vaccine within the past year, which can cause reaction to a TST On the other hand, many have lived in conditions conducive to transmission of M. tuberculosis and we can t do an investigation TUBERCULIN SKIN TESTING OF FOREIGN-BORN ADOPTEES General Guidelines 1. Assess for symptoms of tuberculosis disease prolonged (>2 wk) cough, weight loss, fevers 2. Note a BCG scar and/or immunization records 3. Place and read a 5 TU TST without controls 4. Delay or repeat the TST if the child is significantly malnourished [but watch out for boosting!] 5. Positive TST reaction is 10mm, though this will result in some overtreatment due to recent BCG vaccination 6. Treat LTBI with isoniazid unless specific evidence of INH-resistance is uncovered

7 Interferon γ tests o o o o o MTB specific antigens: Genes in region of difference (RD1) on MTB genome Culture filtrate protein 10 (CFP-10) Early secretory antigen target 6 (ESAT-6) TB7.7(p4) in QuantiFERON Gold In-Tube Identifies LTBI &/or disease Does not cross react with BGC vaccine or most other mycobacteria Requires: single medical visit [for LTBI, not for exposure] blood collection laboratory equipment and personnel Results in hrs Commercial Tests QuantiFERON-TB Gold Company: Cellestis, Australia US FDA approved for adults but not for children In-Tube improvement o Method: Whole blood Incubated with MTB antigens (ESAT-6, CFP-10, TB7.7 {p4}) T-Cells produce INF- γ Supernatant removed INF- γ measured by ELISA reader T-Spot.TB or ELISPOT Company: Oxford Immunotec, UK USFDA approved for adults but not for children o Method: T-cells Incubated with MTB antigens (ESAT-6 & CFP-10) T-Cells produce INF- γ IFN- γ binds to antibody in wells Spots develop and are counted manually or by reader QuantiFERON -TB Gold IT: ELISA Interpretation of test result Antige n From: QuantiFERON -TB Gold IT product insert

8 Positive T-Spot Negative T-Spot Comparison of Tuberculin Skin Test and Interferon- ٢ Release Assays Tuberculin Skin Test IFN- ٢ Release Assay Antigens studied Many -PPD ESAT-6, CFP-10,TB7.7 Cross-reactivity with BCG Yes Unlikely Cross-reactivity with NTM Yes Less Likely Estimated sensitivity, TB in immunocompetent adults 75-90% 75-95% Estimated specificity, TB in immunocompetent adults Distinguish between TB infection and TB disease 70-95% % Boosting Yes No Patient visits required Two One No No Sensitivity and Specificity QuantiFERON-TB Gold Sensitivity* (95%CI) Mori ( 04) 89 (82-94) Ravn ( 05) 85 (72-94) Kang ( 05) 80 (67-90) Pai ( 05) 75 (64-85) Specificity+ (95%CI) Mori ( 04) 98 (95-99) Ravn ( 05) 97 (87-100) Kang ( 05) 96 (90-99) Goletti ( 05) 90 (68-99) T-Spot.TB or ELISPOT Sensitivity* (95%CI) Lalvni ( 01a) 96 (85-99) Lalvni ( 01b) 80 (66-90) Pathan ( 01) 92 (74-99) Chapman ( 02) 92 (81-98) Liebeschuetz( 04) 83 (75-89) Meier ( 05) 97 (90-100) Specificity+ (95%CI) Lalvni ( 01a) 91 (80-98) Pathan ( 01) 100(89-100) Meier ( 05) 92 (62-100) *Sensitivity in pts with active TB, Cx = Gold standard +Specificity in healthy low risk patients without TB Pai, Expert Rev Mol Diagn. 6(3): (2006)

9 T-CELL ASSAYS FOR TUBERCULOSIS IN CHILDREN More data available for ellispot technique More specific for tuberculosis infection; especially useful in low prevalence conditions; previous BCG vaccination Sensitivity is a bigger issue; important in high prevalence conditions [recent contact] Dynamics of tests are largely unknown Results have been highly variable, and indeterminate results are common with QuantiFERON-TB Gold Interferon γ Test Problems For Children Variable sensitivity (75-97%) in active TB disease Specificity reported high (95%) but no gold standard for LTBI and concordance estimates 60-90% with TST and Interferon γ tests Cut-offs not determined specifically for children Indeterminate results in as many as 21% of children [mostly failure of positive control]; correlate with young age and immune status Risk:Benefit ratios are different for children!!! INTERFERON-GAMMA RELEASE ASSAYS CDC expert panel likely to recommend: 1. No preference for one test over the other 2. Should replace the TST for most adults and older children, except, perhaps, for immune compromised; less clear for children < 5 years of age 3. Can be used in contact investigations [even in contact investigations, many adults with a positive TST and history of BCG likely do not have LTBI]

10 IGRA s FOR DIAGNOSING LTBI IN CHILDREN? Does young age (i.e. immunologic immaturity), in itself, decrease sensitivity of IGRA s? To what age can adult data be extrapolated to children? When does a study of children have relevance for infants? Specifically, how do IGRA s perform in young household contacts (sensitivity)? How would IGRA s be integrated into algorithms for window prophylaxis? How do IGRA s perform in diagnosing LTBI in BCG vaccinated young immigrant children (specificity)? What is the effect of prior NTM or BCG exposure on sensitivity? How are IGRA results affected by: Remote versus recent Mtb exposure; Short versus long-term incubation times? Changing cut-offs to enhance specificity and sensitivity? IGRAs IN CHILDREN SOME UNANSWERED QUESTIONS Should +TST in a BCG-vaccinated child always be followed by an IGRA? Should only IGRAs be used in a previously BCGvaccinated child? Low risk child, TST > 15 mm, IGRA neg. Treat or no treat? High risk child [contact], TST > 10 mm, IGRA neg. Treat or no treat? Are IGRAs sufficiently sensitive for contact investigation of young children? Should we use IGRA for TB exposure in children [means two blood draws]? IGRAs AND THE 2009 AAP RED BOOK Can use IGRAs in immunocompetent children > 4 years of age in all situations when a TST would be used Particularly useful/preferred for children who have received a BCG vaccination Use with caution in children < 5 years of age, immunocompromised children Neither IGRAs nor the TST are perfect; always need clinical judgment!

11 TRANSITIONS IN TUBERCULOSIS Susceptible Exposed Infected *Diseased Sick Diagnosed Treated Cured HOW IS TUBERCULOSIS DIAGNOSED? Adults Mycobacterial-based diagnosis positive sputum AFB smear - 60% - 75% positive sputum culture - 90% positive tuberculin skin test - 80% [HIV < 50%] Children positive sputum or gastric AFB smear - 10% positive sputum or gastric culture - 10% - 40% positive tuberculin skin test - 50% - 80%

12 DIAGNOSIS OF TUBERCULOSIS The diagnosis of tuberculosis in children relies on careful and thorough assessment of all the evidence derived from a careful history, clinical examination and relevant investigations, e.g. the tuberculin skin test [TST], chest radiography [CXR] and sputum smear microscopy. Stop TB Partnership Childhood TB Subgroup DIAGNOSIS OF TUBERCULOSIS Even in developed countries, the gold standard for the diagnosis of tuberculosis in children is the triad of: 1. a positive TST 2. an abnormal CXR and/or physical exam 3. a history of recent contact to an infectious adult case of TB CLINICAL SCORING SYSTEMS FOR TUBERCULOSIS IN CHILDREN 17 scoring systems published since 1950 point systems (5) diagnostic algorithms (2) diagnostic classifications (5) combinations (5) 7 systems evaluated [none in HIV+ children] 5 prospective, 2 retrospective, none controlled

13 OBTAINING CULTURE AND AFB SMEAR SAMPLES FROM CHILDREN Traditional method is gastric aspiration, performed as an inpatient on 3 consecutive mornings expensive, invasive Bronchioalveolar lavage has no advantage Nasopharyngeal aspiration few studies Other sites yields usually 0% - 25% culture positive, <10% smear positive INDUCED SPUTUM COLLECTION IN CHILDREN Zar et al. Lancet 2005; 365: 130. Can be done inpatient or outpatient Infection control precautions important Salbutamol, followed by 15 minutes of 5% hypertonic saline solution Sputum obtained via suction with a nasopharyngeal catheter Yield: 30% to 40% culture positive MICROSCOPIC OBSERVATION DRUG SUSCEPTIBILITY [MODS] Oberhelman et al. Pediatrics 2009;118:e100 Compared isolation with L-J slants N=165 subjects < 12 years of age 38 positive specimens from 15 patients {22 G asp., 12 NP asp., 4 stool} MODS: 33/38 [87%] positive L-J slant: 21/38 [55%] positive Median time: MODS-10 days, L-J-24 days

14 NUCLEIC ACID AMPLIFICATION FOR CHILDHOOD TB DISEASE Few recently published studies Most older studies gave yields similar to culture for gastric aspirates [30%-40%] Results do come back faster Specificity not 100% [but usually > 95%] Bottom Line: little help INTERPRETING CHILDREN S CHEST RADIOGRAPHS FOR TB Rarely available in highest prevalence areas Marked inter- and intra- observer variability Reliable in expert hands and in the presence of suspicious symptoms Commonest picture is persistent opacification together with enlarged hilar or subcarinal lymph nodes [though nodes not always discernable] The x-ray is usually sicker than the patient! CHEST RADIOGRAPH TECHNIQUE FOR CHILDREN Check for three important features 1. Rotation can make mediastinum be wider 2. Inspiration when inadequate, can cause mass effect of mediastinum, hilum 3. Penetration difficult to interpret if x-ray is too white or too black

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18 THE PROBLEM WITH CT SCANS The Clinical Problem A child with a positive TST/IGRA has a normal chest x-ray. A CT scan of the chest is done, and shows hilar adenopathy and/or a 5mm nodule in the periphery of the right middle lobe. What do you do?

19 DIAGNOSTIC PEARLS FOR CHILDHOOD TUBERCULOSIS In contact investigations, be wary when the TST/IGRA is negative but the CXR is positive [according to the radiologist]! Positive TST/IGRA in a foreign-born child with pneumonia does not diagnose TB! If you having trouble deciding if a CXR is abnormal, it probably doesn t matter! Just treat with something! TUBERCULOSIS IN HIV-INFECTED CHILDREN Clinical and Radiographic Presentation in children with preserved immunocompetence, presentation is indistinguishable from HIV-uninfected children most common symptoms remain malnutrition, fever, night sweats, lymphadenopathy and cough extrapulmonary disease (meningitis and tuberculoma, abdominal) is more common TB meningitis has the same clinical and CSF findings as in HIVuninfected children except that intracerebral mass lesions are more common chest radiograph findings are typical, but more extensive and a broader differential diagnosis TUBERCULOSIS IN HIV-INFECTED CHILDREN Diagnostic Considerations Diagnosis of TB remains a problem, even in the best of centers broader differential diagnosis Culture yields are about the same for HIV-infected and HIV-uninfected children when controlled for extent of disease Tuberculin skin test is useful in immunocompetent HIV-infected children but usefulness diminished with worsening immunocompromise Interferon release assays - little data for HIV-infected children

20 BCG Disease Hesseling et al. Clin Infect Dis 2006; 42:548 BCG disease diagnosed in 25 children over 3 years 17/25 were HIV-infected; 2 had other immunocompromise Overall, 22 (88%) had local disease, 8 (32%) had distant or disseminated disease; 5 (20%) had both Of HIV-infected children, 6 (35%) had disseminated disease Mortality rate for disseminated disease - 75% NEEDED IMPROVEMENTS IN DIAGNOSIS OF CHILDHOOD TUBERCULOSIS Further characterize the T-cell assays Refine and validate clinical scoring systems Study all tests in HIV-infected children Make chest radiography more readily available much more important role for children than for adults Pediatricians must advocate for resources MOST IMPORTANT Design TB control programs to link children with likely source cases CONTACT TRACING!!!