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

• Tuberculosis infection is caused by mycobacterium tuberculosis which is transmitted from person to person by inhalation of aerosols from an affected individual with active TB.
• Tuberculosis may be spread through cough, sneezing, singing, spitting, or even talking because these particles may remain suspended in the air for several hours.

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

Presumptive TB

Place patient on RIPE (rifampin, isoniazide, pyrazinamide, ethambutol)

Did the specimen sent for culture at the initial evaluation return positive?

Yes

No

Give isoniazide and rifampin for 4 months

Was there cavitation on initial chest X-ray?

No

Is the patient HIV positive?

No

Yes

Yes

Give isoniazide and rifampin for 4 months

Give isoniazide and rifampin for 7 months

Do's

• The content in this section is in bullet points.

Don'ts

• The content in this section is in bullet points.