Micro Flashcards
It’s your first day at the DC CHC and a homeless man comes into the clinic who you suspect has latent TB. What test would be best to use and why?
- TST skin test
- IGRA
- CSR with follow up
- culture with follow up
IGRA. Interferon gamma release assay. It measures the release of IFN gamma from Th1 cells.
Its good for homeless patients because it can be done in one visit and it doesn’t cause false positives if someone was vaccinated. This patient is at high risk for reactivation.
Why might someone get a false + or - with the TST skin test?
False + b/c someone recently was given the BCG vaccine within the past few yrs, or they have another mycobacterial infection.
False - b/c of recent infection, or infant anergy
You have a patient with an extensive travel hx and hacking wet cough, who appears to have cavitations in their lungs, as seen by CXR. What should you do next?
1) smear
2) culture with liquid
3) Xpert MTB/RIF
4) TST
culture with liquid- quick 2 wks. Gold standard
Xpert MTB/RIF. This is used when you know someone has TB and you want to know if it’s a resistant strain.The patients extensive travel hx would warrent this. He may have been exposed to MDR TB which is important to find out prior to treatment, so that you don’t fail or increase resistance.
smear-non-specific AFB (acid fast bacilli)
TST and IGRA are is used to identify those with latent infections
You have a patient sent to you by the health department when it was discovered they had a positive TST test. Assuming they were not recently vaccinated (within the last few yrs) what would be the next best step?
A) Treat with INR, RIF, EMB, and PZA
B) Liquid culture
C) CXR
D) smear and CXR
If they do have latent TB what do you do next?
A) Treat with INR, RIF, EMB, PZA
B) Determine if they’re high risk before you decide whether to treat them or not
C) Spinal x-ray to rule out Potts
D) Treat RIF 3 months or isoniazid for 6-9 months
C) CXR reveal the extent of the infection
Treatment listed is for active infection and a smear is non specific
D) this is the proper treatment for latent infection. The high risk argument is related to administration of the BCG vaccine.
Why does an IGRA not give you false positives if someone was vaccinated before?
The test is measuring the amount of IFN gamma release from your Th1 cells in response to ANITGENS specific to M.tuberculosis. The vaccine is a live attenuated strain of M. tuberculosis. This means your body has been sensitized to the bacterium itself, and not some proteins associated with it, so it won’t react to ??????
How are Mycobacterium avium and intracellulare transmitted and what type of infection does that typically lead to?
ingestion (these two are common in the USA), disseminated infection is common
Describe some important features of M. tuberculosis
It’s outter wall contains mycolic acid and lipoarabinomannan making it hydrophobic and waxy. It’s acid fast on staining (meaning that during carbol fusion a lypophilic agent is heat driven into the bacteria (along with the pink stain) and is not washed away during decolorization), aerobic (loves the lungs), grows in unactivated MO in the lungs after they’re phagocytosed, and they’re non motile.
Why might you use an auramine O dye for M. tuberculosis ?
If you want to image it with fluorescent microscopy because its more sensitive to binding mycolic acid
What medium do you use to grow TB?
Lowenstein jensen medium
Describe the BCG vaccine how it helps and when its contraindicated
Bacille calmette Guerin vaccine is a live attenuated strain of mycobacterium which has decreased the incidence of disseminated disease and infant meningitis. It can cause hypersensitivity reaction and is NOT for the immunocompromised.
Primarily for those without TB infection at high risk aka healthcare workers travelers.
