Tuberculosis%20-%20pulmonary%20(pediatric) Diagnosis
Diagnosis
- Depends on history, clinical exam and relevant laboratory tests
- Patients with cough of ≥2 weeks duration and/or abnormal chest radiograph result prompts evaluation for tuberculosis (TB)
Classification
- Determining the type of pulmonary tuberculosis (PTB) case will aid in appropriate treatment and follow-up
- Based on the site of disease, result of bacteriological tests, PTB severity and previous intake of antituberculous agents
Any of the following:
- ≥2 initial sputum smear tests positive for acid-fast bacilli (AFB)
- 1 sputum smear test positive for AFB plus chest X-ray findings consistent with active PTB, as verified by a clinician
- 1 sputum smear exam positive for AFB plus sputum culture positive for M tuberculosis
- Includes patients without smear results
- At least 3 sputum smear tests negative for AFB, and
- Chest X-ray findings consistent with active PTB, and
- Absence of response to any course of broad-spectrum antibiotics, and
- Physician’s decision to treat with a full course of antituberculous agents
- A laboratory diagnosis; should be carried out at referral centers
- Patient is in contact with a known case of drug-resistant TB
- Patient is not responding to antituberculous treatment regimen or there is recurrence of TB after adherence to treatment
- Usually due to noncompliance and incorrect use of anti-TB drugs
- Patients with active TB disease caused by bacteria that are resistant to at least 2 of the most commonly used drugs for treatment are considered to have MDR-TB
- Patients with history of treatment for TB infection, drug-resistant TB contacts, residence in a country with high rate of drug resistance, poor response to standard anti-TB drugs, positive sputum smears or culture ≥2 months after starting appropriate therapy are at high risk for drug-resistant TB infection
- Management should be individualized
- A type of MDR TB resistant to treatment with Isoniazid and Rifampicin, with additional resistance to any fluoroquinolones and at least 1 of 3 injectable 2nd-line agents used against PTB
- Patient with MDR TB who is noncompliant and misused anti-TB drugs, or individuals in contact with a known case of XDR TB are at high risk for XDR TB
History
- In the early stage, most patients with primary tuberculosis (TB) are asymptomatic
- If child becomes symptomatic, their most common presentation are unremitting cough for >21 days, fever >38°C for 14 days which is not due to any other cause, and weight loss or failure to thrive
- Progression of TB disease is higher in infants and postpubertal adolescents; disseminated disease is more likely in children <4 years old
- Patients who are recently infected with TB (eg close contacts of person with active TB disease, persons immigrated from places with high TB rates, children <5 years old with positive TB test) or those with weak immune system (secondary to comorbidities or treatments) have higher risk for active TB disease progression
- The younger the patient, until the age of 5 years, the higher the risk for TB disease to progress
- Patients who are recently infected with TB (eg close contacts of person with active TB disease, persons immigrated from places with high TB rates, children <5 years old with positive TB test) or those with weak immune system (secondary to comorbidities or treatments) have higher risk for active TB disease progression
Physical Examination
- There are no specific findings that can confirm presence of pulmonary tuberculosis (TB)
- Growth assessment should also be included
- Presence of gibbus and enlarged cervical lymphadenopathy may be indicative of extrapulmonary TB and further evaluation may be needed
Laboratory Tests
Purified Protein Derivative (PPD)-Tuberculin Skin Test (TST)
Nuclear Acid Amplification Test (NAAT)
Line-Probe Assay
- Standard screening test for pulmonary tuberculosis (PTB) infection
- A useful tool in diagnosing PTB disease when used in conjunction with signs, symptoms and other diagnostic tests
- Intradermal injection of 0.1 mL PPD
- Amount of induration is measured 48-72 hours after administration
- Induration started at >72 hours after PPD administration is still considered positive; those seen <24 hours may be caused by immediate hypersensitivity reactions to tuberculin or other constituents of the preparation, hence not considered a positive result
- Considered positive in the following circumstances:
- ≥5 mm induration in patients suspected to have tuberculosis (TB) disease, in close contact with known or suspected contagious people with tuberculosis disease, human immunodeficiency virus (HIV)-infected or other immunosuppressed patients, those who are receiving immunosuppressive drugs and patients who have indications for present or previous TB disease
- ≥10 mm induration in patients who are considered to have an increased likelihood to acquire latent TB infection (LTBI) (eg those living in areas endemic of PTB and those with occupation-related exposure), patients with medical conditions at increased risk to develop LTBI and in patients at increased risk of disseminated TB disease (eg <4 years of age; with other medical conditions like malnutrition, lymphoma, diabetes mellitus; patients born in or who travel in endemic regions of the world; and patients frequently exposed to HIV-infected adults, homeless, institutionalized)
- ≥15 mm induration in patients ≥4 years of age without any risk factors and for all other individuals
- A positive PPD-tuberculin skin test indicates infection but does not necessarily indicate an active disease
- Previous Bacille Calmette–Guérin (BCG) vaccination can cause false-positive TST result, especially if ≥2 BCG vaccines have been given
- TST result of ≥5 mm is considered positive regardless of a child’s vaccination history
- Previous Bacille Calmette–Guérin (BCG) vaccination can cause false-positive TST result, especially if ≥2 BCG vaccines have been given
- A negative finding does not exclude the diagnosis of active PTB
- Very young age, malnourishment, immunosuppression caused by disease or drugs, viral infections (eg measles, mumps, varicella, influenza), live-virus vaccination, overwhelming TB, or corticosteroids can all decrease patient’s skin test reaction
- Should be given on the same day as vaccination with live-virus vaccines or after 4-6 weeks from administration of live-virus vaccine
- Sensitivity develops 3 weeks up to 3 months after the initial infection
- If PTB is being considered, acid-fast bacilli (AFB) smear should be done, with 3 sputum specimens submitted for evaluation, amounting to at least 3 mL (ideal volume: 5-10 mL)
- Direct microscopy of the sputum to detect AFB is the most important test in patients with suspected PTB
- 1st bacteriologic evidence of the presence of mycobacteria
- Provides presumptive diagnosis of active TB and estimates the number of bacilli on the smear which implies infectivity of the patient
- Sputum is the best specimen in patients >10 years and who can expectorate
- Bacterial yields are higher in children >5 years old, adolescents and in children with severe disease
- 3 sputum specimens must be submitted
- Gastric aspirate/lavage may be obtained in younger patients who are unable or unwilling to expectorate sputum
- 3 early morning gastric aspirates are collected on consecutive days
- Based on studies, sputum induction has a good or even better bacteriological yield than gastric aspirates
- Each specimen submitted for TB evaluation should undergo culture for M tuberculosis in both liquid and solid media
- Used to confirm the diagnosis and test for drug susceptibility
- Gold standard in diagnosing TB, however has limited use due to paucibacillary nature of PTB and difficulty of specimen collection in children
- Both liquid and solid cultures may be done to increase sensitivity for M tuberculosis
- A liquid culture is both sensitive and with faster results but contamination-prone
- A solid culture is less sensitive and with slower results but less contamination-prone than liquid culture
- Recommended as a confirmatory test for suspected TB patients with negative sputum smear microscopy and Xpert MTB/RIF results
- Recommended for children with increased risk for TB Infection
- Specimens that can be used include sputum brought about by coughing, induction or nasopharyngeal suctioning, gastric extracts and bronchoalveolar lavage
- Only way to differentiate M tuberculosis from other nontuberculous mycobacteria
- Indicated in patients who have one or more of the following:
- Suspected drug resistance
- Complicated or severe cases of disease
- HIV infection
- Uncertain diagnosis
- May not be done if epidemiologic, skin test, and X-ray information are consistent with TB
Nuclear Acid Amplification Test (NAAT)
- May be used when it is difficult to diagnose TB infection and when rapid confirmation is needed to rule out other diagnosis when AFB smear, Xpert MTB/RIF, and TB cultures are negative
- Not for routine initial evaluation of patients suspected to have TB but is particularly helpful in diagnosing children with pulmonary disease that are immunocompromised
- Recommended in AFB smear-negative patients with moderate to high probability of TB infection
- Not recommended for patients with low-risk for TB since false-positive results are common
- Acceptable NAAT are Hologic Amplified M tuberculosis direct (MTD) test and Cepheid Xpert MTB/RIF test
- A highly sensitive and specific cartridge-based fully automated NAAT for the detection of M tuberculosis and Rifampicin resistance
- 68% sensitive, 99% specific when compared to sputum culture
- 88% sensitive and 98% specific when compared with smear microscopy
- 94% pooled sensitivity, 98% pooled specificity for Rifampicin resistance
- 84.9% sensitive for extrapulmonary TB (eg lymph nodes, lung aspirates)
- 79.5% sensitive for cerebrospinal fluid (CSF) analysis for TB meningitis
- Recommended as an initial diagnostic tool for the following:
- Suspected TB patients able to produce sputum samples
- Patients suspected to have multidrug resistance or HIV-associated TB rather than using other diagnostic tests (eg sputum microscopy, culture, drug susceptibility tests)
- Seriously ill patients able to produce sputum samples
- CSF examination of patients suspected to have TB meningitis
- Patients with non-sputum specimens (gastric lavage fluid, other non-respiratory specimens) at high risk for extrapulmonary TB
- Recommended as a confirmatory test for suspected TB patients with negative sputum smear microscopy results
- 1 sputum specimen for Xpert MTB testing is comparable to that of 2 sputum specimens in smear microscopy
- Detects patient’s T cells generated interferon-γ in response to M tuberculosis antigens
- IGRAs available:
- QuantiFERON TB gold in tube (QFT-GIT): Detects the level of IFN-γ in the plasma by means of enzyme-linked immunosorbent assay (ELISA); QuantiFERON-TB gold (QFT-G) test
- T-SPOT.TB test (T-SPOT): Detects T cells that emit IFN-γ by means of enzyme-linked immunospot (ELISPOT) assay
- May be used in patients belonging to low-middle class families suspected of TB or latent TB infection
- Interpret results with caution in children <5 years old and immunocompromised patients
- IGRA is preferred over TST in patients ≥5 years old with high probability of M tuberculosis infection, LTBI suspected, with low to intermediate risk towards developing TB, BCG-vaccinated or may not follow up for TST result
- If IGRA is not accessible, a TST may be done instead
- If the initial test is negative, a second test is performed (eg if the initial test is TST and the result is negative, IGRA, is then performed or vice versa)
- If the second test is positive, the patient is considered to have M tuberculosis infection
- There is no need for patients with low risk for TB disease undergo M tuberculosis examination, except in certain conditions (eg as instituted by law), in which IGRA is performed in patients ≥5 years old and a second test is advised
- May be used in patients >3 years old if necessary
- An immunocapture assay recommended to assist in detection of active TB in HIV-positive patients especially in hospitalized patients with signs and symptoms of TB, severe HIV, or CD4 cell count of <200 cells/mm3
- May be considered in outpatient setting in patients with signs and symptoms of TB and CD4 cell count of <100 cells/mm3
- In patients who are either positive for AFB smear or Hologic Amplified MTD, a rapid molecular DST for Rifampin, with or without the inclusion of Isoniazid should be done if any of the following are present:
- History of TB treatment
- Birthplace or place of residency for 1 year is in a country wherein the average prevalence of TB is ≥20/100,000 or MDR TB is ≥2%
- With exposure to MDR TB patients
- With HIV
- Culture-based DST is the gold standard in the detection of drug resistance and the rapid molecular DST is only for a selected few such as those enumerated above
- Active TB must be ruled out before initiating LTBI therapy since IGRA and TST cannot differentiate active from latent TB, but only indicate M tuberculosis infection
Line-Probe Assay
- A rapid molecular-based DST that provides result for Isoniazid or Rifampicin within 1-2 days which can be used in deciding the treatment appropriate for the patient
- Confirmatory diagnostic tool for sputum smear-positive patients and culture-positive TB isolates
- 1st-line line-probe assays may be used as the initial test instead of phenotypic culture-based DST to detect resistance to Rifampicin and Isoniazid for sputum smear-positive patients or a cultured isolate of M tuberculosis complex
- Includes INNO-LiPA Rif.TB assay, GenoType® MTBDRplus, GenoType® MTBDRplus version 2 and GenoscholarTM NTM+MDRTB II
- 2nd-line line-probe assay (eg GenoType® MTBDRsl assay) may be used as the initial test to detect resistance to fluoroquinolones and 2nd-line injectable medications in patients diagnosed with MDR-TB or Rifampicin-resistant TB (RR-TB) instead of phenotypic culture-based DST
Human Immunodeficiency Virus (HIV) Testing
- Should be offered to pediatric patients with presumptive and diagnosed TB at high risk for HIV infection
Imaging
Chest X-ray
- Useful in the diagnosis of pulmonary tuberculosis (PTB) but is not specific (98% sensitive, 75% specific for any abnormality suggestive of TB)
- Lateral X-ray increases the sensitivity of diagnosis in detecting hilar adenopathy
- Lymphadenopathy or calcification are common findings in primary TB but may also be seen in other viral, bacterial, or fungal infections
- Presence of uniform stippling in both lungs may highly indicate TB in children
- The following findings are suggestive of PTB:
- Persistent lung opacification, miliary pattern may also be noted
- Enlarged hilar or subcarinal lymph glands
- Adolescent patients may have findings similar to adult patients (eg pleural effusions, apical infiltrates with cavity formation)
- May also develop primary disease with collapse lesions and hilar adenopathy
Computed Tomography (CT) Scan
- May help in diagnosing TB when X-ray results are normal but TB infection is clinically suspected
Screening
Exposure/Latent Infection
- Latent tuberculosis infection (LTBI) occurs after M tuberculosis-containing infective droplet has been inhaled
- LTBI is considered in children who have reactive tuberculin skin test (TST) but with no clinical and radiographic manifestations
- Patients with untreated LTBI have 40% chance of developing TB which is highest during the first 2 years of infection
- Includes preventive treatment after exposure without evidence of infection and treatment of latent infection
- There is currently no available definitive examination for the determination of LTBI
Screening and Latent TB Infection Should be Considered in the Following:
- All household contacts with a smear-positive PTB source case are recommended to be screened for symptoms of disease
- Includes patients <3-5 years of age; the likelihood of developing disease after infection is much greater in patients <5 years compared to ≥5 years of age
- Patients ≥5 years of age, if symptomatic
- With medical conditions (eg HIV, diabetes mellitus, malnutrition, chronic dialysis, leukemia) or with intake of drugs that cause immunosuppression
- Patients who have chest X-ray findings suggestive of old TB
- Have purified protein derivative (PPD)-tuberculin skin test results converted to positive after 1-2 years
- Institutionalized patients in hospitals
- Patients residing in overcrowded areas (eg orphanages, shelters and prisons)
- Individuals working in the bacteriology section of the laboratory
- Those who are living or working in a community that serves as an environment for TB exposure
- People who came from countries with increased incidence of TB disease
Diagnostic Tests for Suspected Extrapulmonary Tuberculosis
- Cell counts and laboratory chemistries
- Adenosine deaminase (ADA)
- Free Interferon-γ (IFN-γ)
- For pleural or peritoneal TB
- AFB smear microscopy
- Mycobacterial cultures
- Should be sent to a regional laboratory for genotyping
- Nucleic acid amplification test
- Negative results should not rule out the possibility of extrapulmonary tuberculosis
- Histological examination