Introduction
Tuberculosis is an infection by Mycobacterium tuberculosis. The HIV/AIDS pandemic has fueled the resurgence of the disease and the widespread occurrence of drug resistance. The most common presentation is an infection of the lungs, called pulmonary tuberculosis.
Transmission and Diagnosis of TB
Tuberculosis is usually spread by droplet infection. When a person with tuberculosis (TB) coughs, talks, spits or sneezes, large numbers of mycobacteria are released. Inhalation of only a small number of the organisms is enough to initiate an infection.
Tuberculosis is suspected with a medical history of long-standing cough with blood-streaked sputum, low-grade fever, chest pains and weight loss. Characteristic findings on chest X-ray examinations are highly suggestive. Laboratory testing includes a skin test, a blood test and sputum smear test and culture. The growth of the organism on culture of laboratory specimen is definitely diagnostic.
How the Sputum Test Works
Sputum samples are collected in special containers issued from the laboratory. The patient is instructed to cough up phlegm (not just saliva) and spit it into the container. This is best done in the morning and in a secluded place to reduce risks of spreading the infection. Steam inhalation or some mild exercise may be required to loosen the phlegm in some cases.
A sample of the phlegm is taken and smeared on a glass slide. Mycobacteria have a peculiar cell coat that retains acid dyes. This is the basis of a peculiar staining technique that identifies them under the microscope. They are identified as acid-fast bacilli (rods) under the microscope.
Further examination of the sputum sample is done by culture of the specimen. This is necessary, whether the organism is seen under the microscope or not. Here, a sample of the sputum is placed on special media and incubated. The growth of mycobacterium tuberculosis in this way is definitive diagnosis. This culture serves to distinguish mycobacterium tuberculosis from other mycobacteria that may or may not cause disease in humans. The culture also serves to provide ample opportunities to try for drug sensitivity or resistance and select the appropriate antituberculous drug for treatment.
