Mycology and Mycobacteriology

The Vermont Department of Health Laboratory cultures and identifies Mycobacterium tuberculosis, the causative agent of tuberculosis (TB) and other pathogenic Mycobacterium species from all specimen types.

• There is no fee for mycobacteriology test services.

• Isolates that cannot be identified at the Laboratory may be forwarded to National Jewish Health for identification.

• Rapid, direct detection of M. tuberculosis in respiratory specimens is available on demand for patients who have not started TB treatment. All first time smear positive and provider requested respiratory specimens are tested.

  • The GeneXpert MTB/RIF Assay detects M. tuberculosis and resistance to the important TB treatment drug rifampin in sputum specimens.

  • The Amplified M. tuberculosis Direct (MTD) test detects M. tuberculosis in bronchoscopy specimens.

• If rifampin resistance is detected by GeneXpert, the specimen is referred to CDC for gene sequencing.

• Rapid molecular detection of drug resistance is available at a designated CDC laboratory for all M. tuberculosis isolates suspected to have drug resistance.

Guidelines for using nucleic acid amplification tests to aid TB diagnosis and airborne infection isolation decisions:

• More information on the diagnosis of active tuberculosis disease from the CDC

• Guidelines for Submission of Sputum Specimens for Tuberculosis Testing

• Availability of an Assay for Detecting Mycobacterium tuberculosis, Including Rifampin-Resistant Strains, and Considerations for Its Use — United States, 2013

• More information on the diagnosis of active tuberculosis disease from the CDC

• Consensus statement on the use of Cepheid Xpert MTB/RIF®assay in making decisions to discontinue airborne infection isolation in healthcare settings

The Vermont Department of Health Laboratory accepts all specimen types submitted for culture of both mycobacteria and fungi. Yeasts are identified via biochemical testing with API ID32C. Fungal isolates are referred to reference laboratories for identification.

Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis. Not everyone infected with TB bacteria becomes sick. As a result, two TB-related conditions can exist: latent TB infection (LTBI) and active TB infection.

Culture of the bacteria, molecular assays, and blood tests can be performed to determine if a person has been exposed to TB. The blood test utilized at the Vermont Department of Health Laboratory is called the QuantiFERON-TB Gold Plus (QFT-Plus).  

• The QFT-Plus is an interferon-gamma (IFN-y) release assay, commonly known as an IGRA, and is a current alternative to the tuberculin skin test (TST or Mantoux). Unlike the TST, the QFT-Plus is a controlled laboratory test that requires only one patient visit and is unaffected by previous vaccination with Bacille-Calmette Guerin (BCG).

• The QFT-Plus consists of a 4-tube collection system optimized with tuberculosis-specific antigens that elicit both CD8 and CD4 T cell responses.  It has been shown that CD8 T cells have a higher frequency of detection in people with active TB disease vs. latent infection and allows for greater detection in active TB subjects with HIV co-infection and in young children.

• A positive QFT-Plus is a strong indicator of exposure to TB, but it cannot differentiate between active infection with TB and latent tuberculosis infection (i.e. a person who has no signs or symptoms of disease). 

• Positive QFT-Plus results are used in conjunction with risk assessments, radiography, and other medical and diagnostic evaluations by the patient’s doctor.