Tuberculosis infection occurs when a subject inhales the Mycobacterium
tuberculosis bacilli (MTB). An active case of pulmonary or laryngeal tuberculosis
generates infectious particles called droplet nuclei of <5 microns in diameter, when
coughing, sneezing or through any other forceful expiratory maneuver. The
infectiousness of a patient with TB is directly related to the form of the disease
(laryngeal, pulmonary), the presence of cough, cavitary lung disease and the positivity
of the sputum smear/culture.
The prevalence of M. tuberculosis infection among household contacts is higher than
50%. Contacts who are <5 years of age or HIV infected have the most significant risk
of developing tuberculosis once they acquire the infection.
In latent tuberculous infection, most bacilli are metabolically inactive, and only a few
are replicating. In immunocompetent individuals, these bacilli are destroyed by the
immune defenses of the host and the development of active disease aborts. When the
immunity of the subject fails, the bacilli multiply, and eventually, active tuberculosis
ensues. If latent infection tuberculosis is not treated, approximately 5% of infected
individuals will develop the active disease within the first two years after infection, and
another 5% will develop TB sometime later in life.
HIV infection is the most significant risk factor for the progression of LTBI to active
TB disease, with an annual risk of 7-10% for subjects who are not receiving highly
active antiretroviral treatment.
Keywords: Cavitary disease, Cough, Droplet nuclei, Immunity, Latent
tuberculosis infection, T lymphocytes.Cavitary disease, Cough, Droplet nuclei, Immunity, Latent
tuberculosis infection, T lymphocytes.
