mycobacterial (TB)

Question 1

Testing for Latent TB infection (LBTI) (2)

Answer 1

• two accepted but imperfect tests :
  TST (tuberculin skin test)
  and
  IGRA (Gamma Interferon (IFN-γ) Release Assay)
• both tests depend on cell-mediated immunity (memory T-cell response), and neither test can accurately distinguish between LTBI and active TB disease
• not useful if it is active TB

Question 2

Active TB : Microbiological tests & Histopathology
*Early morning __: at least 2 (normally 3 specimens)
*Nasogastric aspirate (in children who can’t expectorate sputa)
*Urine __ __ (renal TB)
*CSF – AFB smear, culture, PCR
*Biopsy specimens: lymph nodes, bone, pleura
*Fluid: peritoneal fluid, pleural fluid, pericardial fluid
*Blood culture in miliary TB
Acid fast smear staining methods :
*Auramine phenol fluorescence technique (for screening)
*Ziehl-Neelsen (for confirmation)
Histology: presence of caseating granulomas and__ __ __

Answer 2

*Early morning SPUTUM: at least 2 (normally 3 specimens)
*Nasogastric aspirate (in children who can’t expectorate sputa)
*Urine AFB culture (renal TB)
*CSF – AFB smear, culture, PCR
*Biopsy specimens: lymph nodes, bone, pleura
*Fluid: peritoneal fluid, pleural fluid, pericardial fluid
*Blood culture in miliary TB
Acid fast smear staining methods :
*Auramine phenol fluorescence technique (for screening)
*Ziehl-Neelsen (for confirmation)
Histology: presence of caseating granulomas and Acid Fast Bacill

Question 3

Active MTB – culture (this takes 24H): solid vs liquid media

Answer 3

*15 to 20 hours replication time (compared to common bacteria < 1 hour)
*Special culture media is used for MTB, incubation over 8 weeks (common bacteria 2-5days)

Solid media ie. Löwenstein-Jensen Culture takes 3 to 8 weeks!
*glycerol to encourage
Mycobacterial growth
* malachite green to reduce
growth of other organisms
/ contaminants

WHO recommends liquid
medium culture :
Mycobacterial Growth
Indicator Tube (MGIT)
* Reduces growth to 1 to
3 weeks

Question 4

ACTIVE TB - TREATMENT
*___ patient if admitted to hospital
*Empirical treatment with 4 drugs – ___
*No drug resistance – continued with __and __
*Usual duration of treatment – ___ (UTI or celulitis only few days)
*Beware of TB drugs interacting with ___ medications!
*___ – for drug compliance (see MDR TB later): prevents antibiotic resistance
When is a patient no longer infectious?
*Generally after ___ of effective treatment in drug-sensitive TB.
Other supporting signs –
_ consecutive AFB smear negative specimens, clinically improved
*More stringent criteria for MDR TB

Answer 4

*Isolate patient if admitted to hospital
*Empirical treatment with 4 drugs – Rifampicin, Isoniazid, Ethambutol, Pyrazinamide
*No drug resistance – continued with Rifampicin and Isoniazid
*Usual duration of treatment – 6 months (UTI or celulitis only few days)
*Beware of TB drugs interacting with HIV medications!
*Directly observed therapy (DOT) – for drug compliance (see MDR TB later): prevents antibiotic resistance
When is a patient no longer infectious?
*Generally after 2 weeks of effective treatment in drug-sensitive TB.
Other supporting signs –
3 consecutive AFB smear negative specimens, clinically improved
*More stringent criteria for MDR TB

Question 5

MTB – who is at increased risk?

Answer 5

*Intense exposure
*Immigrants from developing countries
*Malnutrition
*Alcoholics
*Homeless
*IV drug abusers
*Prison inmates
*Elderly people
*Very young
*HIV patients
*Immunocompromised

Question 6

MTB – mode of spread?

Answer 6

Most likely and common via :
Inhalation of droplet nuclei, aerosolised by coughing, sneezing,
talking
Risk of infection – closeness of contact & infectivity of patient
Sputum acid fast bacili (AFB) smear positive – highly infectious
Sputum AFB smear negative, culture positive – less infectious