Tuberculosis, or TB, is a bacterial infection caused by Mycobacterium tuberculosis that most often affects the lungs. This reference helps students compare TB transmission, latent infection, active disease, diagnosis, and treatment. It is useful because TB remains a major global health concern and requires careful public health control.
Students need to understand both the biology of infection and the reason treatment must be completed exactly as prescribed.
TB spreads through airborne droplet nuclei when a person with infectious pulmonary or laryngeal TB coughs, speaks, or sings. Latent TB infection means bacteria are present but inactive, while active TB disease means bacteria are multiplying and can cause symptoms and transmission. Standard drug-susceptible active TB treatment often begins with RIPE therapy: rifampin, isoniazid, pyrazinamide, and ethambutol.
Diagnosis may involve symptom review, chest imaging, sputum testing, nucleic acid amplification tests, culture, and drug susceptibility testing.
Key Facts
- TB is mainly transmitted by inhaling airborne particles from a person with infectious pulmonary or laryngeal TB.
- Latent TB infection usually has no symptoms, is not contagious, and may be detected by a TB skin test or interferon-gamma release assay.
- Active pulmonary TB commonly causes cough lasting 3 weeks or longer, fever, night sweats, weight loss, fatigue, chest pain, or coughing blood.
- A common first-line active TB regimen is RIPE: rifampin + isoniazid + pyrazinamide + ethambutol during the initial phase.
- Drug-susceptible active TB is often treated for at least 6 months, commonly 2 months of RIPE followed by 4 months of rifampin and isoniazid.
- Sputum smear microscopy can show acid-fast bacilli, but culture and drug susceptibility testing are needed to confirm the organism and resistance pattern.
- Multidrug-resistant TB is TB resistant to at least isoniazid and rifampin, the two most important first-line TB drugs.
- Incomplete or irregular treatment increases the risk of relapse, ongoing transmission, and drug-resistant TB.
Vocabulary
- Mycobacterium tuberculosis
- The slow-growing bacterium that causes tuberculosis infection and disease.
- Latent TB infection
- A state in which TB bacteria are present in the body but inactive, causing no symptoms and no spread to others.
- Active TB disease
- A condition in which TB bacteria multiply and cause illness, and pulmonary or laryngeal disease can be contagious.
- RIPE therapy
- A first-line TB drug combination using rifampin, isoniazid, pyrazinamide, and ethambutol.
- Drug susceptibility testing
- Laboratory testing that identifies which TB medicines are likely to work against a patient’s TB bacteria.
- Directly observed therapy
- A treatment support method in which a trained person observes a patient taking TB medicines to improve adherence.
Common Mistakes to Avoid
- Confusing latent TB infection with active TB disease is wrong because latent TB has no symptoms and is not contagious, while active pulmonary TB can spread to others.
- Stopping TB medicines when symptoms improve is wrong because surviving bacteria can multiply again and may become drug resistant.
- Assuming a negative early sputum smear rules out TB is wrong because smear tests can miss cases and culture or molecular testing may still detect TB.
- Using only one TB drug for active disease is wrong because combination therapy is needed to prevent resistance and fully treat the infection.
- Ignoring drug susceptibility results is wrong because resistant TB requires a different regimen and may not respond to standard first-line treatment.
Practice Questions
- 1 A patient begins standard drug-susceptible TB therapy with 2 months of RIPE followed by 4 months of rifampin and isoniazid. What is the total planned treatment length in months?
- 2 A clinic identifies 18 close contacts of an infectious TB case. If 6 contacts have a positive TB test, what fraction and percent of contacts tested positive?
- 3 A sputum culture report shows resistance to isoniazid and rifampin. What type of TB resistance pattern does this meet, and why is it important?
- 4 Explain why completing the full TB treatment course protects both the patient and the community.
Understanding Tuberculosis & TB Treatment Reference
After inhalation, TB bacteria can reach the tiny air sacs of the lungs. Immune cells called macrophages swallow the bacteria, but the bacteria can survive inside these cells. The body may build a wall of immune cells around the infection.
This structure is called a granuloma. It can keep bacteria controlled for years without removing every bacterium. If immune defenses weaken later, bacteria may begin multiplying again.
Risk rises with HIV infection, diabetes, poor nutrition, smoking, certain cancer treatments, or medicines that suppress the immune system. This is why a past exposure can become active disease long after the original contact.
Tests answer different parts of the TB problem. A skin test or blood test shows that the immune system has recognized TB proteins. It cannot by itself show whether a person has active disease.
A chest image can reveal changes such as cavities or areas of inflammation, yet images cannot prove TB because other illnesses can look similar. For suspected lung disease, a sputum sample is especially important. A rapid molecular test can detect genetic material from TB and may identify some drug resistance quickly.
Culture grows the organism in a laboratory. It takes longer because TB grows slowly, but it provides strong evidence and allows detailed drug susceptibility testing.
The medicines in the initial treatment attack TB in different ways. Isoniazid interferes with construction of the bacterial cell wall. Rifampin blocks an enzyme needed to make RNA, a molecule used to produce proteins.
Pyrazinamide works particularly well against bacteria living in acidic parts of an infection. Ethambutol slows cell wall production and helps protect the regimen until resistance results are known. Using several medicines reduces the chance that a naturally resistant group of bacteria will survive.
These drugs can cause important side effects. Rifampin can turn tears, sweat, urine, or saliva orange. Isoniazid can affect nerves or the liver.
Ethambutol can affect vision. Students should remember that side effects need prompt medical advice, not silent stopping of treatment.
TB control involves more than giving tablets. Health workers may use directly observed therapy, in person or by video, to help patients take doses reliably. This approach can identify barriers such as transport problems, unstable housing, cost, stigma, or confusion about instructions.
Close contacts may need evaluation because early detection prevents future illness. In healthcare settings, ventilation, respirators, and isolation rooms reduce exposure to airborne particles. Drug resistance develops through natural genetic changes followed by selection.
When treatment is missed or the wrong regimen is used, susceptible bacteria are killed while resistant bacteria can remain. Careful testing, steady treatment, and support for patients protect both the individual and the wider community.