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  • Technical Bulletin
  • Tuberculosis and Bacillus Testing

Nevada State Public Health Laboratory Guidance for Tuberculosis and Bacillus Testing

Background

The purpose of this technical bulletin is to provide guidance on two Nevada State Public Health Laboratory (NSPHL) specimen/isolate submission updates: 1) Mycobacterium tuberculosis (MTB) rapid test utilizing the Cepheid GeneXpert MTB/RIF (rifampin resistance) assay for sputum and non-sputum samples; and 2) sentinel laboratory criteria for submission of isolates suspected of Bacillus anthracis and Bacillus cereus biovar anthracis.

CepheiD genexpert MTB/RIF asssay for rapid detection of Mycobacterium tuberculosis

The performance of the Xpert MTB/RIF assay was evaluated and FDA-approved using induced or expectorated sputum samples. Testing of non-sputum, clinical specimens has not been evaluated and may affect the test performance. Due to recent changes in FDA oversight of laboratory-developed tests, modifications have been made regarding what the NSPHL is authorized to develop and offer for off-label testing. For non-sputum and non-sputum concentrate specimens, the NSPHL will no longer offer MTB rapid testing using the Xpert MTB/RIF assay. However, Xpert MTB/RIF testing of sputum specimens remains a key rapid diagnostic test performed by the NSPHL.

The Centers for Disease Control and Prevention recommends the clinical best practice of collecting a sputum specimen from all adults with suspected pulmonary TB, regardless of bronchoscopy specimen.† A post-bronchoscopy sputum specimen is more ideal for acid fast bacillus smear, culture, and rapid Xpert or PCR analysis. Additionally, commercial reference laboratories are validated and available to perform direct-PCR testing for the detection of the MTB on clinical non-sputum specimens.

Sentinel clinical laboratory guidelines for sample submission of isolates suspected of bacillus anthracis and bacillus cereus biovar anthracis

Before submitting isolates suspected of Bacillus anthracis or Bacillus cereus biovar anthracis to the NSPHL for Laboratory Response Network for Biological Threats (LRN-B) testing, sentinel laboratories must combine morphological differentiation with the performance of several conventional tests.

These tests and the results that require further LRN-B testing are:

  1. Gram Stain: Demonstrates spore-forming, large gram-positive bacilli.
  2. Catalase Test: Positive result.
  3. Hemolysis: Observation of no beta hemolysis after 24 hours of incubation. Note: Beta hemolysis rules out both B. anthracis and B. cereus biovar anthracis.

The NSPHL has changed the LRN-B final reports to indicate findings for both B. anthracis and B. cereus biovar anthracis.

Questions

For updated guidance, review the Division of Public and Behavioral Health Technical Bulletin web page regularly. Email StateLab@unr.edu or call 775-682-6240 for other questions regarding tuberculosis and Bacillus testing.

References

†Lewinsohn, D., Leonard, M., LoBue, P., et al. Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children. Clin Infect Dis 2017; 64: e1-e33.