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Laboratory:

Clinical Microbiology

Test Name:

MYCOBACTERIA (ACID-FAST BACILLI [AFB]), CULTURE, CUTANEOUS

Test Code: AFBSK

Clinical Information:

Test Indications:
Skin biopsy samples may be submitted from patients suspected of having a cutaneous infection caused by a nontuberculous mycobacteria (NTM), such as M. fortuitum, M. abscessus, M. chelonae, M. marinum and M. ulcerans, or tuberculosis (TB) affecting the skin, specifically cutaneous TB.

Recommendations:
Culture from the drainage material or a tissue biopsy are recommended for the identification of NTM. (American Thoracic Society Documents)
The Canadian Tuberculosis Standards recommend that:
“Diagnosis of cutaneous TB is made by biopsy, with histopathologic assessment and mycobacterial smear and culture. Non-TB mycobacteria and leprosy may also manifest as skin disease, underscoring the diagnostic importance of appropriate tissue-sample testing.”
“Every person with presumed extra-pulmonary TB should also be assessed for pulmonary TB to assess infectiousness and potentially assist with diagnosis.”
“In general, tissue has a higher yield than liquid/biologic fluids.”
Shared Health Testing Process - Every AFB skin sample culture is evaluated by microscopy and culture. Smears are reported semi-quantitatively (Negative or 1+ to 4+). Cultures are incubated for 7 weeks and reported as soon as growth is detected.
The nucleic acid amplification test (NAAT)/PCR is NOT validated for skin samples.
M. tuberculosis are routinely referred to the NRCM-NML for susceptibility testing. Susceptibility testing for nontuberculous mycobacteria may be requested by consultation with the Shared Health Microbiologist-on-call.
If Mycobacterium ulcerans is suspected clinically, the laboratory must be notified as prolonged culture incubations may be required.

Shared Health Testing Process - Every AFB skin sample culture is evaluated by microscopy and culture. Samples are decontaminated and concentrated prior to microscopy and culture. Smears are reported semi-quantitatively (Negative or 1+ to 4+). Cultures are incubated for 8 weeks and reported as soon as growth is detected.
The nucleic acid amplification test (NAAT)/PCR is NOT validated for skin samples. The in-house NAAT only identifies the presence of M. tuberculosis. Following consultation with the microbiologist-on-call, any requests for NAAT for NTM are referred to the National Reference Centre for Mycobacteriology - National Microbiology Laboratory (NRCM-NML).
The identification of M. tuberculosis, Mycobacterium avium complex and Mycobacterium gordonae is performed in-house. Other AFB-positive organisms are referred to the NRCM-NML for identification. Susceptibility testing for M. tuberculosis is performed routinely by the NRCM-NML. Susceptibility testing for nontuberculosis mycobacteria may be requested by consultation with the Shared Health Microbiologist-on-call.
If Mycobacterium ulcerans is suspected clinically, the laboratory must be notified as prolonged culture incubations may be required.

Patient Preparation Instructions:
Patients' sample collection should be conducted in accordance with Infection and Control Practices. The WRHA Acute Infection Prevention and Control Manual states that "when collecting specimens for suspected or active TB, specimens must be collected utilizing Airborne Precautions regardless of age".
Accurate patient identification must be made prior to sample collection. Patient identification should be done in accordance with site policy.
Samples and requisitions must be labeled/completed in accordance with the Shared Health Specimen Acceptance Policy.

Collection Devices:

Preferred Device:	1 - Sterile Specimen Container (100 mL) Sterile Specimen Container (100 mL) Manufacturer: Catalogue #:
Alternate Device:	1 - eSwab eSwab Manufacturer: Catalogue #: - *Suboptimal specimen.

Swabs are SUBOPTIMAL specimens. Dry swabs and ear swabs will be rejected as inappropriate specimens.

Specimen Required:

Skin biopsies - as much as possible (Adult and Pediatric)
Tissue sample may be submitted fresh or in a small amount of normal saline. Fluid should be aspirated by syringe following the removal of the surface exudate with sterile saline or 70% alcohol.
Do not add preservatives or additives. Formalin-fixed samples cannot be cultured and will be rejected.

Referral:

Ensure samples that are being sent to a referral laboratory are packaged in accordance with Transport of Dangerous Goods recommendations for diagnostic samples.

Requisition:

_SH Microbiology - Provincial Requisition (R250-10-06)

Reference Values:

Microscopy: No acid-fast bacilli observed.
Culture: No acid fast bacilli isolated after 7 weeks of incubation.

Availability:

Weekdays

Weekdays (Monday - Friday). Mycobacteriology cultures are only performed at the Health Sciences Centre in Winnipeg. AFB positive smears of specimens are phoned to the nursing unit immediately. Culture positive index cases of M. tuberculosis are phoned to the nursing unit immediately.