Download Tuberculosis (TB)

Tuberculosis (TB)
PHCL 442 Lab Discussion
Jamilah Al-Saidan, M.Sc
Topics we will cover in TB..
• Tuberculin PPD skin test
• Booster phenomenon
• BCG vaccine
• TB & pregnancy
• TB & Lactation
• TB & pediatrics
Tuberculin PPD Skin Test
• Also known as Mantoux method
• Detects infection with M.tuberculosis & not necessary for
diagnosis of active TB
• PPD = Purified Protein Derivative of M.tuberculosis
Tuberculin PPD Skin Test
• Done by injecting 0.1 ml of 5-TU PPD intradermally into the
dorsal surface of forearm
• If a patient has previously been infected with M.tuberculosis
sensitized T cells are recruited to the skin site where they
release cytokines
• These cytokines induce an induration (raised area) through
vasodilatation, edema, fibrin deposition, and other
inflammatory cells to the area.
• Measure the diameter of the induration to interpret the results
TU = Tuberculin Unit
• Reaction best to be interpreted 48-72 hours.
• Measure the diameter of the induration in millimeters to
interpret the results
PPD Skin Test
PPD Skin Test
Reading PPD Skin Test
The person's medical risk factors determine at which increment (5 mm, 10 mm, or 15
mm) of induration the result is considered positive
≥ 5 mm
≥10 mm
Recent contact to someone
Patient with DM
with active TB
Patient with fibrotic
changes on the CXR
consistent with old TB
Patient with CRF
Organ transplant patient
Patient with leukemia or lymphoma
HIV patient
Recent immigration <5 years from area
with high prevalence of TB
Immunosuppressed patient Employee of high risk settings
Children < 4 years
Mycobacteriology lab personnel
Injection drug abusers
≥15 mm
No risk factor
for TB
Does a Positive Test Indicate a TB
Diagnosis??
• No- hence the term false-positive
• To confirm diagnosis must obtain a culture
• AFB (sputum smear)
AFB = Acid Fast Bacilli
False Positive Results
• Previous administration of BCG vaccine
• Cross reaction with other mycobacterial species
• Qualified, experienced person must read the test
BCG= Bacillus of Calmette-Guerin
Does a Negative Test Eliminate a TB
Diagnosis??
• No
• 25% false negative results during initial evaluation of patients with active
TB
• False –ve results can occur in:
1. In persons who have had no prior infection with M.tuberculosis
2. Who have only recently been infected
3. Who are anergic
Does a Negative Test Eliminate a TB
Diagnosis??
Anergy
•
Decreased ability to respond to Antigens
•
Caused by:
1.
Old age/ newborns
2.
Corticosteroids
3.
Immunosuppressive drugs
4.
HIV infection
5.
Recent viral infection
6.
Malnutrition
False Negative Results
Factors due to the person
being tested
Factors due to
administration
Factors due to
tuberculin used
Factors due to
reading the test
Live virus vaccination
SQ injection
Improper storage
In-experienced
reader
CRF
Injecting too little
Contamination
antigen
Recent TB infection (within 810 weeks of exposure)
Corticosteroids &
immunosuppressant agents
age (less than 6 months old,
elderly)
Bacterial, viral or fungal
infection
Error in recording
Booster Phenomenon
• When a person experience a significant increase in the size of
a tuberculin skin test reaction that may not be caused by
M.tuberculosis
• Could be due to:
 PPD skin test performed every 1-2 years
 Prior BCG vaccine
 Other mycobacteria
Booster Phenomenon
• Use two-step testing for initial skin testing of adults who will be
retested periodically (e.g., health care workers). The incidence of
this phenomenon appears to increase with age.
• This ensures that any future positive tests can be interpreted as being
caused by a new infection. Done for new employees.
1. Return to have first test read 48-72 hours after injection
If first test is positive, consider the person infected.
If first test is negative, give second test 1-3 weeks after first injection
2. Return to have second test read 48-72 hours after injection
If second test is positive, consider person previously infected
If second test is negative, consider person uninfected
A person who is diagnosed as "infected" on two-step testing is called a
"tuberculin converter".
BCG Vaccine
• Derived from an attenuated strain of M.bovis
• Vaccine efficacy only ≤80%
• More effective if given in childhood
•
Not recommended during pregnancy or for HIV infected
individuals
• Prior vaccination can cause positive PPD skin test
• Side effects: prolonged ulceration at the vaccination site,
lupoid reactions & death
BCG: Bacillus of Calmette and Guerin Vaccine
TB & Pregnancy
• Untreated TB represents a greater risk to a pregnant women
and her fetus than treatment
• INH, rifampin, ethambutol & streptomycin have all been
reported to be teratogenic in animals but no human reports
• Studies have shown that INH, rifampin, & ethambutol are safe
in pregnancy & can be used to treat TB and treatment should
be continued for 9 months
TB & Pregnancy
• All pregnant women on INH should receive pyridoxine 25 mg
/day to prevent CNS toxicity
• Pyrazinamide have no enough data to support its use in
pregnancy, only reserved for cases of drug resistance
• Streptomycin is used only as a last resort due to fear of
ototoxicity in infants
INH = Isoniazide
CNS = Central Nervous System
TB & Lactation
• Only minimum amounts are excreted in breast milk
• Lactation is safe during anti-TB treatment
TB & Pediatrics
• Whenever a diagnosis is suspected start treatment due to risk
of disseminated TB in children
• Same drugs for adults can be used
• Examine routinely for signs and symptoms of hepatitis,
increase in LFT 2-3 times normal are common but benign and
often transient.
• Except for ethambutol not because it is more toxic but its more
difficult to assess visual acuity in children
TB & Pediatrics
• In pediatrics three drugs are enough for treating TB
• Start with INH 10 – 15 mg/kg/day + Rifampin 10 – 20
mg/kg/day + Pyrazinamide 15 – 30 mg/kg/day  2 months
• Continue with INH 20-30 mg/kg/dose + Rifampin 10-20mg/kg
/dose (two or three times weekly)  4 months
• Use ethambutol 15 – 20 mg/kg/day or streptomycin 20 – 40
mg/kg/day in cases of resistance only