Tuberculosis is a contagious disease that primarily affects the pulmonary system and causes a chronic cough, chest pain and sometimes the coughing up of blood. People with an active infection can infect others by coughing, sneezing, and talking. The “American Journal of Respiratory and Critical Care Medicine” reports that approximately ten percent of infected individuals will develop active tuberculosis The classifications of tuberculosis are based upon exposure history, infection and whether the disease is latent or active.
Class 0
Individuals are placed in this class if they have had no exposure to tuberculosis and have a negative tuberculin test. This test determines if a person has already been infected with tuberculosis mycobacteria by measuring how sensitive a person’s immune system is to proteins, called tuberculins, from the tuberculosis mycobacteria cultures. In a tuberculin skin test, the tuberculins are injected under the skin. After 48 to 72 hours the size of induration, or hardening of the skin, is evaluated.
Class 1
Individuals placed in class 1 have been exposed to tuberculosis, but did not have a positive tuberculin skin test. Treatment for latent tuberculosis infection should be initiated if the person is immune compromised and especially if they are HIV positive. A joint statement prepared by the American Thoracic Society and the Centers for Disease Control and Prevention recommends that persons with latent tuberculosis infection be treated daily with isoniazid for nine months. Other recommended alternative treatments include a two month daily regimen of rifampin and pyrazinamide or rifampin alone for four months.
Class 2
Individuals placed in class 2 have a positive tuberculin skin test, but no evidence of active tuberculosis. Some persons in class 2 may be treated for latent tuberculosis infection.
Class 3
Individuals placed in class 3 have active tuberculosis and exhibit symptoms of the disease. Patients with active tuberculosis may have abnormalities in the upper lung lobes that can be detected by a chest radiograph. Patients with past active tuberculosis may have nodules and fibrotic scars in the upper lung lobes. Individuals in class 3 will remain in class 3 until treatment of tuberculosis is completed. The American Thoracic Society, the Centers for Disease Control and Prevention and the Infectious Disease Society of America recommend all adults with active tuberculosis disease begin treatment with a two month initial phase of isoniazid, rifampin, purasinamide and ethambutol. At the end of two months patients are then treated either four months or seven months with isoniazid and rifampin depending on whether lesions were initially observed in the lungs and if bacterial cultures are positive after the initial treatment period.
Class 4
Individuals who do not have active tuberculosis disease, but have had a previous episode of tuberculosis and have a positive reaction to the tuberculin skin test are placed in class 4.
Class 5
Individuals placed in class 5 are suspected of having tuberculosis, but have a pending diagnosis. After a tuberculin skin test, mycobacterial culture and chest x-ray the person should be classified in one of the other preceding classes.
References
- “American Journal of Respiratory and Critical Care Medicine”; Diagnostic Standards and Classification of Tuberculosis in Adults and Children
- Centers for Disease Control and Prevention: Targeted Tuberculin Testing and Treatment of Latent Tuberculosis Infection
- Centers for Disease Control and Prevention: Treatment of Tuberculosis
