Tuberculosis resident survival guide
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Moises Romo M.D.
Synonyms and keywords:TB, PPD, mycobacterium tuberculosis
Overview
Tuberculosis (TB) is a common and very contagious infectious disease caused by Mycobacterium tuberculosis bacteria (MTB). MTB can affect every system of the human body, but most commonly affects the respiratory system since this organism grow vigorously in high oxygen environments. It is calculated that more than a third of the world's population has been exposed to MTB, being the vast majority of them asymptomatic and maintaining as latent. Symptoms of respiratory active tuberculosis includes hemoptysis, shortness of breath, fever, chills, night sweats, and weight loss. Usually latent tuberculosis is treated with a regimen of 6-9 months of rifampin or isoniazid, while active TB is managed with a phase of four antituberculous agents (rifampin, isoniazid, ethambutol, pyrazinamide) for 2 months to later be continued only by isoniazid and rifampin 4 more months.
Diagnostic Criteria
Test for latent tuberculosis
- Tuberculin skin test. Also known as Mantoux test or PPD consists in the visualization of the skin reaction after the injection of M. tuberculosis antigens 24, 48, and 72 hours after. A positive result is interpreted as the following:
- >5 mm: HIV infected patients, CXR that suggests TB infection, individuals taking steroids
- >10 mm: Healthcare workers, nursing home dweller, parenteral drug users, patients with immunocompromised diseases
- >15 mm: All individuals not cathegorized above
- QuantiFERON-TB. Detects cell-mediated immunity to tuberculin
- QuantiFERON-TB Gold. Detects IFN-g released by sensitized T cells by M. tuberculosis antigens in vitro
- T SPOT-TB. Detects T cells stimulated by M. tuberculosis
- AMPLICOR assay. Uses DNA polymerase chain reaction (PCR) to amplify nucleic acid targets.
Tests for active tuberculosis disease
- Microbiological detection:
- Acid fast bacilli stain. This tests is relatively fast and cheap but presents with a high number of false positives, since may detect Mycobacterium bovis or NBT
- Mycobacterial culture. This test is cheap but takes weeks to have results. Culture may be done in 3 types of media: solid media (Lowenstein Jensen), agar-based media (Middlebrook 7H10 and 7H11), and liquid media (Middlebrook 7H12).
- Nucleic acid amplification assays. This test is rapid and specific to M. tuberculosis but costly and gives no drug susceptibility
- Response to therapy. Clinical response to antituberculous drugs may be an indicator of TB infection, but lead time bias should assesed
Causes
Life Threatening Causes
Life-threatening causes include conditions that may result in death or permanent disability within 24 hours if left untreated.
Common Causes
Complete Diagnostic Approach
Shown below is an algorithm summarizing the diagnosis of Tuberculosis according the the Association of chest physicians guidelines.
| Presumptive TB | |||||||||||||||||||||||||||||||||||||||||||||||||
| Sputum examination + Chest X-ray | |||||||||||||||||||||||||||||||||||||||||||||||||
| Sputum positive for TB, Chest X-ray suggestive of TB | Sputum positive for TB, Chest X-ray not suggestive of TB | Sputum negative for TB, Chest X-ray suggestive of TB | Sputum negative for TB, Chest X-ray not suggestive of TB | High clinical suspicion for TB | |||||||||||||||||||||||||||||||||||||||||||||
| Cartridge-Based Nucleic Acid Amplification Test | |||||||||||||||||||||||||||||||||||||||||||||||||
| Mycobacterium tuberculosis detected | Mycobacterium tuberculosis not detected or Cartridge-Based Nucleic Acid Amplification Test result not available | Considere alternate diagnosis | |||||||||||||||||||||||||||||||||||||||||||||||
| Rifampicin sensitive | Rifampicin indeterminate | Rifampicin resistant | Clinically diagnosed TB | Alternate diagnosis | |||||||||||||||||||||||||||||||||||||||||||||
| Microbiologically confirmed TB | Repeat Cartridge-Based Nucleic Acid Amplification Test on 2nd sample | Refer to management of Rifampicin resistance | |||||||||||||||||||||||||||||||||||||||||||||||
| Indeterminate of 2nd sample, collect fresh sample of liquid culture/ Line Probe Assay | |||||||||||||||||||||||||||||||||||||||||||||||||
Do's
- The content in this section is in bullet points.
Don'ts
- The content in this section is in bullet points.
References
Treatment
Shown below is an algorithm summarizing the treatment of disease name according the the [...] guidelines.
Do's The content in this section is in bullet points. Don'ts The content in this section is in bullet points. References
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