Tuberculosis resident survival guide

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Moises Romo M.D.

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.

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.

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

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.