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