Transcript Standards for Laboratory Diagnosis of Tuberculosis

Standards for Laboratory
Diagnosis of Tuberculosis
Professor Brian I. Duerden
Inspector of Microbiology and Infection
Control,
Department of Health
TB diagnosis and management
depend upon a reliable and prompt
laboratory service
Guidance and Standards
National SOP
– How to do the tests
NICE guidance
– How to manage the patient
DH programme
– What service should be delivered
– 3 working groups
TB monitoring and laboratory
services working group
Surveillance standards
Standards for laboratory diagnosis
– Current best practice
– Simple and straightforward
– Not replicate or replace the National SOP
Standards to cover
Samples
Transfer to laboratory
Immediate tests
– Microscopy
Culture, isolation and
identification
Laboratory facilities
and expertise
Transport
Susceptibility testing
Molecular
fingerprinting/typing
Notification
PCR detection of Mtb
Immunodiagnostic
tests
Histopathology
Samples
Type of sample
– Sputum (resp. sample), CSF (spinal/paraspinal/intra-cerebral), gastric washings, lymph
nodes (tissues), urine, faeces
Number of samples
– 2 or 3 for sputum? Consecutive days.
– Early morning or any time?
– True LRT specimen
Documentation
Transfer to laboratory
Within 24h (or 1 working day, max 48h)
– Minimise overgrowth
– Maintain AFB character
Potentially infected clinical sample
– Routine procedure
Immediate tests
Microscopy
– Auramine fluorescent staining
– 6-day service (not on call)
– Perform microscopy and issue result within 24h (1
working day) of receipt
– Telephone positive result to senior member of clinical
team
– Notify lead TB nurse, lead clinician, CCDC
Accreditation; IQC programme; satisfactory EQA
performance; staff CPD/peer review
Culture, isolation and identification
Automated liquid culture on all samples
– Set up within 24h of receipt (6 day service)
– Plus conventional solid culture
Send all isolates to RCM on day found to
be positive
– Reach RCM within 24h
Complete identification of most
mycobacterial isolates within 21 days
Identification and reporting
NAAT (PCR, LCR) or hybridisation gene
probe for Mtb complex
– On the day culture shows positive OR
– Within 24h of receipt at RCM
Other probes and/or phenotypic tests
Report on day of test to
– Senior member of clinical team
– Lead TB nurse, lead TB clinician, CCDC
Laboratory facilities and expertise
Safety – Category 3 for culture
– HSE approved
– Contingency plan for accidental dispersal
– Continuity plan for closure
Accredited
– IQC programme, satisfactory EQA
Sufficient number – daily service,
competence
Named Consultant and BMS for advice
Transport
Samples
– Potentially infected samples (routine)
Positive cultures
– Category A but exemption to treat as B for
clinical and diagnostic purposes
UN 3373 – marked Diagnostic or Clinical
P650 packaging
Do not send by Royal Mail
Susceptibility testing
Complete within 30 days of initial receipt of
clinical sample for primary agents
– Isoniazid, rifampicin, pyrazinamide, ethambutol
Takes 10-20 days by liquid proportion (automated) or
resistance ratio
Molecular detection
– Rifampicin within 24h if MDRTB suspected
– Isoniazid under development
Done at RCM with accreditation, IQC, EQA
Molecular fingerprinting/typing
ALL ISOLATES
– 15-loci MIRU-VNTR
Mycobacterial Interspersed Repetitive Units –
Variable Number Tandem Repeats
– Results to national database
– Other techniques as appropriate
Done at RCM
Laboratory notification
HPA
– Via CoSurv from laboratory that identifies a
positive culture
– Confirmation of positive from RCM within 24h
(1 working day) of receipt
– RCM reports culture and susceptibility results
to MycobNET within 24h of report to clinician
PCR detection of Mtb
Not routine
Available from RCM for particular samples
– High suspicion
– Definitive diagnosis deemed to be urgent
– Liaise in advance – Consultany Microbiologist
to RCM
Immunodiagnostic tests
Interferon γ (QuantiFERON-TB Gold)
Activated specific T-cells (T-SPOT.TB)
– Standard under development
Which patients?
How long should it take?
Who provides it?
What do the results mean and who interprets
them?
Histopathology
Report within 3 days of receipt
Inform the Microbiology service
– Ensure same reporting as for positive
microscopy and culture results
Send autopsy samples to Microbiology
without formalin!!
[Role of PCR to be determined]
Implementation of standards
Local responsibility
– What is done where?
Microscopy; culture; identification
– What throughput is needed?
– Equipment – cost-effectiveness
– Personnel
Maintain skills; CPD; peer review
Named individuals for advice
Back-up and cover
– IQC, EQA
Standards for Quality
Only do what you can do properly!