TB is an infectious disease caused by the M. tuberculosis bacteria. TB primarily affects the lungs, but it can infect and damage almost any organ. TB is the leading cause of death from infectious diseases worldwide but is relatively uncommon in the US. TB is primarily transmitted by inhalation of infected droplets that are exhaled when an infectious person coughs, sneezes, or talks.
When infected droplets are inhaled, one of these situations can occur:
- The TB bacterium can be cleared from the body
- Primary progressive TB can occur. An infection can occur, and the patient can rapidly develop active TB
- A TB infection occurs; this is called primary TB
- The TB bacteria are contained, and the patient develops latent TB
- Latent TB reactivation
Approximately 5% to 10% of all persons infected with TB will eventually develop TB, and the risk of this is higher in patients who are immunocompromised or who have a comorbidity that negatively affects the immune system.
The signs and symptoms of TB are non-specific, e.g., cough, fatigue, fever, malaise, and productive cough.
The diagnosis of TB depends on four criteria: Patient risk factors/index of suspicion, signs/symptoms, radiographic evidence, and bacteriologic evidence. Bacteriologic evidence of TB can be obtained by an AFB smear, a TST, an IRGA test, or culturing. Culturing is the definitive proof of a TB infection.
TB infections are drug-susceptible or drug-resistant. Drug-resistant TB is caused by M. tuberculosis organisms that anti-tubercular drugs cannot eliminate. There are two types of drug-resistant TB, MDR-TB and XDR-TB. Drug-resistant TB is uncommon in the US.
All suspected and confirmed TB cases should be promptly reported to local and state public health authorities.
Patients treated for active TB do not need to be hospitalized unless certain conditions are present. Hospitalized TB patients can transmit the disease, and infection control requires using an airborne infection isolation room, standard precautions, airborne precautions, respiratory precautions, and PPE.
With prompt identification of a TB infection and proper care, TB is easily cured. Treatment of TB is done by multi-drug regimens with an initiation and a continuation phase, and depending on the patient's circumstances, the treatment regimens can last at least four months or much longer. Every effort should be made to ensure patient adherence, including DOT, and there are guidelines for handling missed doses and treatment lapses. Adherence to the drug regimen is critically important, as treatment lapses can cause TB relapse, treatment failure, and other serious consequences.
At the minimum, patients receiving drug therapy to treat TB should be evaluated monthly. Clinicians should evaluate the patient's clinical condition, determine if the patient is adhering to the treatment regimen, and look for adverse effects like hepatoxicity, peripheral neuropathy, and visual changes.