Mode of Transmission

TB is transmitted through the air. The droplet nuclei generated when a sputum positive pulmonary TB patients coughs, mixes in the air and are carried to a susceptible person in the vicinity or by air currents to longer distances. Sputum Negative TB patients may also contribute in transmission of infection to a smaller extent.  Primary infection occurs in people who have not had any previous exposure to tubercle bacilli. Droplet nuclei inhaled into the lungs get lodged into the terminal alveoli after having escaped the mucociliary defenses of bronchi. Infection begins with multiplication of the tubercle bacilli in the lungs and the resulting lesion is called a Ghon focus. Lymphatics drain the bacilli to the hilar lymph nodes. The Ghon focus and related hilar adenopathy form the primary complex or Ghon Complex. Bacilli may spread from the primary complex throughout the body.

Prevention of transmission
How to prevent transmission
I Primary Prevention

1) Health Promotion : Health education to patients, contacts and general public about
a) Mode of transmission
b) Disposal of sputum and infective materials
c) Methods to prevent spreads from patients to healthy individuals
d) Regularity of treatment and follow-up
2) Specific Protection :
a) Immunoprophylaxis - BCG vaccination is important component of Universal Immunization Programme (UIP). While it may not protect against development of Tb disease in adults, it protects against severe forms of TB in children e.g. tuberculous meningitis and miliary tuberculosis.
b) Chemoprophylaxis - Isoniazid (INH) is advised in all under six contacts of sputum positive TB patients as a prophylactic agent. It protects against development of serious forms of TB as the cell mediated immunity is immature up to the age of 6 years.

II Secondary Prevention

1) Early diagnosis :
a) All patients with the following symptoms should be subjected to two sputum smear examinations (SPOT-MORNING)
i) Cough for more than two weeks.
ii) Low grade, evening rise of fever and night sweats.
iii) Chest pain
iv) Hemoptysis
b) Contact-Screening: all family members and other close contacts of the pulmonary TB patient are screened for symptoms.
c) Tuberculin testing has less value in detection of Tb in adults but is a useful tool in pediatric TB.
d) X-ray chest is used as a supportive tool in diagnosis of sputum negative pulmonary TB
2) Prompt and effective treatment:
a) Domiciliary mode of treatment
b) Regular administration of drugs and follow-up
c) Directly Observed Treatment-Short Course Chemotherapy (DOTS)
d) Prompt defaulter retrieval actions.

III Tertiary Prevention

1) Disability limitation - can be achieved through early diagnosis, prompt and effective treatment and regular follow-up.
2) Rehabilitation -
a) Occupational rehabilitation may be required in certain cases, due to decreased pulmonary functions.
b) Psychological rehabilitation of cured patients, in view of the social stigma and the false beliefs associated with the disease.