Module 2
TB Disease Transmission & Prevention
Pulmonary TuberculosisPulmonary Tuberculosis Extra -Pulmonary TBExtra -Pulmonary TB
an infectious disease caused byan infectious disease caused bya microorganism calleda microorganism called
Mycobacterium tuberculosisMycobacterium tuberculosis
Tuberculosis
• Transmitted from an infected person through aerosolized droplets formed by coughing, sneezing, talking, laughing, or singing
• Infection is caused by inhalation of droplet nuclei
Transmission
Factors affecting Infectiousness:
• Infecting dose effect - Infectiousness is directly related to the number of tubercle bacilli inhaled
• Virulence – different strains – ability or capacity of agent to cause a disease
• Resistance of the person in danger of being infected – dependent by immune system of person
• The size of the room
• Ventilation
Infectiousness
Infectiousness
Pulmonary and laryngeal TB should be considered infectious if the patient – is coughing or
– has sputum smears positive for acid fast bacilli, and
– is not receiving therapy, has just started, or shows poor clinical response to therapy
Infectiousness
• Patients are NOT considered infectious if they:– Have received appropriate therapy for 2-
3 weeks
– Show favorable clinical response to therapy, and
– Have negative smear results from sputum specimens
TB Infection takes place when the TB bacteria is inhaled and deposited at the air sacs in the lungs
The cilia acts as barrier to protect the body from infection
The macrophage at the air sacs help destroy the TB bacilli in healthy persons
M. Tb
• Most initial infection heals spontaneously as the immune system walls off the organism forming a granuloma.
• Within granulomas are dormant organisms that can reactivate at anytime
• 10% lifetime risk of disease once infected
• Higher risk with immune compromised patients (HIV, diabetes, malnutrition, immunosuppressive therapy, etc.)
Natural Course of the Disease (Pathogenesis)
• Asymptomatic
• Negative sputum smears
• Negative chest x-ray
• Not infectious
• Dormant infection
• Symptomatic
• Positive sputum smears
• Positive chest x-ray
• Infectious
• Active infection
INFECTION
INFECTION versus DISEASE
DISEASE
Exposure
Infection
Disease
Death
5-10% lifetime risk
Untreated, 70% will die in 5 years
A TB patient infects 10-20 persons per year
> 90% CURE RATE (w/ DOTS)
Healthy Individuals
30% of un-treated TB undergoes spontaneous remission
In 90-95% of infected patients, M. tb remains dormant in the body
Only active TB patients, especially smear (+) can infect others
Person X
N o t
I n f ec t ed
The TB Transmission Cycle
Clinical Clinical FeaturesFeatures
Pediatric TBPediatric TB Adult TBAdult TB
Stage of TB infection
Primary tuberculosis
Post-primary, secondary or reactivation TB
Main diagnostic confirmation
Clinical features + history of exposure to a smear (+) case
Bacteriology (AFB smear and, if warranted, culture) Serial chest x-ray
Bacterial load Low load, low infectiousness
High load, high infectiousness
Treatment 2-3 drugs 4-5 drugs
DOT mandatory
Yes – by parent Yes – by health worker
PEDIATRIC versus ADULT TB
• Proper and complete drug therapy
• Proper hygiene
• Adequate ventilation
• UV Light
• HEPA filters
• Use of masks
• Proper and complete drug therapy
• Proper hygiene
• Adequate ventilation
• UV Light
• HEPA filters
• Use of masks
Ways to Reduce Transmission
• Cough of 2 weeks or more
• Chest pains, shortness of breath
• Fever, loss of appetite & loss of weight, a general feeling of illness & tiredness
• Sputum production which may be blood-stained
Signs and Symptoms
Clinical History and Physical Examination
Chest Radiography
Tuberculin Skin Test
Sputum Microscopy
Diagnostic Tools for TB
Sputum examination for AFB or direct sputum microscopy should be the first diagnostic test for patients suspected to have pulmonary TB (PTB).
The National TB Program/DOTS recommends that…
What is the appropriate initial work-up for TB suspects?
Microscopy is more objective and reliable than chest x-ray
Overdiagnosis
Diagnosed byx-ray alone
ActualCases
20
40
60
80
100
0
TB does not show a definite pattern on chest x-ray. 40% of patients diagnosed as having TB on the basis of x-ray alone do not have an active TB.
“Therefore, chest x-ray is unreliable for diagnosing and monitoring treatment of tuberculosis.”
TB does not show a definite pattern on chest x-ray. 40% of patients diagnosed as having TB on the basis of x-ray alone do not have an active TB.
“Therefore, chest x-ray is unreliable for diagnosing and monitoring treatment of tuberculosis.”
Tomas, K. “Tuberculosis case finding and chemotherapy.” WHO, 1979
Conclusion: Role of Chest X-ray