Approach To Detecting TB In Children And Youth

Question 1

What are risk factors for TB

Answer 1

• Indigenous
• overcrowded living conditions
• poorly ventilated houses
• foreign-born children from TB endemic areas
• known contact with infectious source

Question 2

What is the incidence of TB in Canada

Answer 2

• 4.5-4.8/100 000 Canada

- 120-300/100 000 Nunavut

Question 3

What is the BCG vaccine, and what are its contraindications

Answer 3

• live attenuated vaccine given to children residing in jurisdictions with high rates of smear positive TB
• Contraindications: Family or personal hx immunodeficiency

Question 4

How is TB spread?

Answer 4

Breathing air containing aerosolized droplets of Mtb

Question 5

What is the pathophysiology of primary TB infection

Answer 5

Mtb inhaled —> replicated in alveoli —> eaten by macrophages —> form granuloma and hilar/mediastinal LAN

Eventually granuloma calcifies

Can spread to other LN or via hematogenous dissemination

Question 6

How do early primary disease present? What’s percent of exposed children will have primary disease

Answer 6

• Presentation:
  1. Pulmonary disease
  2. extra-pulmonary disease (LAN, meningitis) disseminated disease (+/- meningitis)
• 5-10% cases - highest risk <4yo, within 12mo of initial infection
• <12mo infants highest risk for disseminated disease

Question 7

How does pulmonary TB present

Answer 7

• acute: mimicking PNA
• indolent with wheezing or subacute sx
• CXR: focal pneumonia is, ground-glass opacities, hilar/mediastinal/subcarinal LAN

**CT more sensitive and specific BUT radiation +/- sedation

Question 8

How does disseminated, extra-pulmonary disease

Answer 8

• Wt loss, poor feeding, recurrent/prolonged fever, lethargy, irritability
• can present as PNA (military nodules, ARDS), meningitis, OA infection, refractory sepsis
• can infect: lung, brain, retina, liver, spleen, bone marrow, muscle

Question 9

What does the CSF in TB look like?

Answer 9

Pleocytosis with lymphocytic predominance

Question 10

What is LTBI?

Answer 10

• Occurs in 90-95% of exposed cases
• asymptomatic, normal exam, normal CXR
• TST/IGRA positive

Question 11

What is reactivation disease?

Answer 11

AKA post primary disease

• Pulmonary disease (may be cavity)
• Extra-pulmonary (LAN, meningitis, liver/spleen granulomatous disease, OM, peritonitis, pleural)
• Disseminated

Question 12

How many LTBI develop post-primary disease?

Answer 12

5-10%

Question 13

What are risk factors for reactivation disease?

Answer 13

Immunosuppression - infection, HIV, diabetes
Puberty
Malnutrition
Medications - steroids, biologics

Question 14

What is the approach to diagnosing TB

Answer 14

• CXR + TST/IGRA
  1. If TST/IGRA positive and CXR negative = LBT

2. If TST/IGRA and CXR positive = active TB —> get expectorants sputum, fasting gastric aspirated x 3 for culture
   - send culture for AFB stain, culture, NAAT
   - do HIV serology

Question 15

Pros and cons of TST

Answer 15

TST = done with PPD from heat-inactivated Mtb
Leads to type 4 hypersensitivity reaction
Will be positive with Mtb, NTM, BCG vaccine
Specificity ~60%

Requires follow up at 48-72h, and needs experience measuring it

Can have false negative with immunosuppression

TST more sensitive than IGRA in <2y

Less expensive than IGRA

Question 16

What is an IGRA

Answer 16

IGRA - in vitro test looking at immune response by measuring interferon-gamma released by T-cells in response to antigens specific for Mtb

Question 17

Pros and cons of IGRA

Answer 17

No cross reactivity with BCG
Minimal reactivity with NTM 
Specificity >95%
False negative with immunosuppression
False positive with recent TST 
Less sensitive in <2yo
More expensive

Question 18

What happens if a child is identified as contact of an index case

Answer 18

H+P
CXR
TST now and in 8-10wk
Determine contact cases drugs sensitivities 
Break of contact x 8-10wk 

If <5yo AND TST <5mm = give window ppx (1 drug)
If TST >5mm (initial or after BOC) = treat for LTBI

Question 19

How is TB treated

Answer 19

LBTI - isoniazid, rifampin or rifapentin/isoniazide

Active TB - start with 4 drug regimen