CD - tuberculosis - part 1 Flashcards
what is the agent for TB (1)
1- mycobacterium tuberculosis complex (MTC)
what is the epidemiology of TB in Canada (1)
1- mostly amongst Indigenous (FNIM) and foreign-born populations
what are risk factors for acquiring TB -
(SDoH - 3;
close contact/facilities- 4;
int’l- 1) (8)
1- precariously housed
2- indigenous populations
3- persons who inject drugs
4- residents of LTC
5- inmates at correctional facilities
6- healthcare workers - HCW
7- close contacts of an active case of pulmonary TB
8- immigrants from countries with high incidence (Afghan, China, India, Pakistan, Philippines, Vietnam)
what is the reservoir for TB (2)
1- mostly humans
2- rarely, other primates
what is the reservoir for M. Bovis? (2)
1- cattle and some other animals
2- M. bovis is largely eradicated via pasteurization of milk and tuberculin testing of cattle
what is the mode of transmission for TB (2)
1- airborne
2- via inhalation of bacilli-containing droplet nuclei that reach alveoli
what factors increase the probability of TB transmission?*
(‘testing’- 2
‘symptoms’- 1
‘anatomy’- 2
‘environment - person/place/time’- 3)
(8)
*was on practice exam
1- bacterial burden
2- delays in diagnosis and/or effective treatment
3- amount/severity of cough
4- pulmonary TB with cavitary or upper lung zone disease
5- laryngeal TB > pulmonary TB
6- duration of exposure to case (time)
7- (physical) proximity to source case (person)
8- crowding and poorer room ventilation (place)
describe the ‘bacterial burden’ factor increasing TB transmission (1)
1- smear-positive/culture-positive disease is more transmissible than smear-neg/culture-neg disease
describe the ‘laryngeal TB > pulm TB’ factor increasing TB transmission (1)
1- laryngeal TB symptom of hoarseness is linked with inflammation/ulceration of vocal cords, which is MORE contagious than pulm TB
what is the incubation period for TB (1)
1-
2-10 weeks up to decades
what is the period of communicability for TB -
I) start of communicable period:
a) for smear positive and symptomatic (item 1)
b) for smear negative and asymptomatic, and no cavitation on CXR (item 2)
II) when does the communicable period generally end (3abc)
I) start of communicable period:
1- Longer of: 3 months before onset of respiratory symptoms OR 3 months before first positive finding consistent with TB
2- four weeks before first
positive finding consistent with TB
II) end of communicable period - up to:
3a- receipt of 2-4 weeks of antibiotics +
3b- smear-neg x3 +
3c- clinically improving
are young children with TB infectious? (2)
1- no- younger children with TB are rarely infectious
2- because they have few bacilli and often no sputum production
what is the clinical presentation of pulmonary TB (4)
1- chronic cough >3 weeks, from non-productive to productive
2- sputum sometimes with hemoptysis
3- chest pain
4- shortness of breath
what is the presentation of systemic TB symptoms (B symptoms) (4)
1- fever
2- nightsweats
3- weight loss
4- fatigue
what are potential sites for extra-pulmonary TB (5 examples)
1- brain
2- spine
3- bones
4- kidney
5- lymph nodes
could affect other organs
what is an example presentation of extra-pulmonary TB (1)
1- depends on site affected (e.g. spine TB can have back pain)
is non-respiratory (i.e. non-pulm, non-throat) TB contagious? (1)
1- generally not
of people infected with TB, what is the breakdown between those who stay LTBI and those who become active disease:
A: of total people infected
B: of all the people with LTBI
(4)
A: Of total people infected with TB:
1- ~5% will develop active tuberculosis disease within 18 to 24 months
2- about 95% will develop LTBI
B: Of this 95% LTBI people,
3- ~90% will never develop active TB (stay as LTBI)
4- ~5% will have reactivation TB and develop active disease at any point after initial infection
what are the 2 types of tests that identify TB infection (LTBI) (2)
1- tuberculin skin test (TST)
2- Interferon gamma release assay (IGRA)
what is the tuberculin skin test (TST) (1)
1- intradermal injection of purified protein derivative (PPD) from M. tuberculosis
what is the expected reaction in a person after TST has been administered (2)
1- in someone who was previously infected and developed cell-mediated immunity to these antigens, a delayed hypersensitivity reaction occurs within 48 to 72 h
2- reaction will cause localized swelling/ induration of the skin at injection site
what are contraindications to receiving TST (5)
1- those with previous positive blistering reaction at injection site
2- active TB disease
3- documented hx of adequate TB treatment
4- those with current major viral infections (e.g. measles, mumps, varicella)
5- those received live virus vaccine in past 4 weeks (increases likelihood of false negative)
what is considered a positive result interpretation of a TST, read between 48-72h post-injection (3)
1- <5mm is generally negative
2- ≥5 mm may be positive in select populations (e.g. HIV, known contact with active TB case, immunosuppressed)
3- ≥10 mm is positive in any population considered low risk of disease
define TST conversion (2)
1- TST of 10mm or more when an earlier test was <5mm
2- TST conversion occurs within 3-8 weeks of exposure
who should get a two-step TST (2)
1- health care workers, correctional workers, and other populations at increased risk of TB exposure
2- done if subsequent TSTs will be conducted at regular intervals
why should the defined population group(s) get the two-step TST (2)
1- undergo two-step TST before an exposure to account for “booster effect”
2- i.e. a single TST may elicit little response but may stimulate anamnestic immune response so that a second TST given anytime from 1 week to 1 year later, will elicit a much greater response
how often does two-step TST protocol need to be done (3)
1- needs to be performed and documented ONCE only
2- never needs to be repeated
3- any future TST can be one-step, regardless of duration since last TST
which populations have been seen to have the booster effect from TST testing (3)
1- people with remote TB infection e.g. older adults
2- those with sensitivity to non-tuberculous mycobacterial antigens
3- those with prior BCG vaccination
what is the likelihood that a greater reaction to a second TST test is due to actual infection, if there has not been a TB exposure? (1)
1- in absence of an exposure, the likelihood that the greater reaction to the second test indicates true infection, is LOW
why is it important to make note of the booster effect with TST testing (2)
1- this booster effect is important to detect as it can be confused with new infection if the second test is only performed following exposure to a person with infectious pulmonary TB (I.e. false positive)
2- i.e. if second test was performed w/o exposure, it would still be positive and therefore is just the booster effect
what is the interferon gamma release assay (IGRA) (2)
1- an in-vitro blood test of cell-mediated immune response
2- they detect interferon-gamma released by T cells following stimulation by M. tuberculosis-specific antigens
what is the goal of LTBI diagnosis (1)
1- to identify those at increased risk of developing active TB disease and therefore would benefit from tuberculosis preventive treatment (TPT)
which of TST and/or IGRA can be used for LTBI testing? general (2)
1- both can be used generally when testing for LTBI is needed
2- however there are circumstances where one is preferred over the other
when is IGRA the preferred test for LTBI (4)
1- person received BCG vaccine after 1yo or received multiple BCG vaccine doses
2- personnel trained to administer/read TST are not available
3- person is unlikely or unable to return to have TST read
4- TST is contraindicated
when is TST the preferred test for LTBI (1 + 2 examples)
1- TST preferred when there is a plan to repeat the test later
2- e.g. serial testing in contact investigation
3- e.g. serial testing of HCW or other populations with potential for ongoing exposure
when can both TST and IGRA be used sequentially for LTBI testing? (2)
1- if either TST or IGRA are negative, the other test can be done to increase sensitivity (snOUT), if risk of infection/progression to active disease is high
2- if initial TST is positive but risk of infection is low/risk of false positive is high with hx BCG, can do IGRA to increase specificity (spIN)
in which circumstances is testing for LTBI NOT recommended? (4)
1- testing people who have low risk of infection and a low risk that they will progress to active TB if infected
2- active TB disease in adults and those 12+ old
3- routine/mass screening for LTBI outside contact investigations or occupational screening programs
4- monitoring response to active TB treatment
what are the two testing components of diagnosing active TB disease (2)
1- Chest x-ray for screening
2- microbiology (acid fast bacilli smear, and culture, or NAAT) for confirmation
what CXR findings are indicative of active TB disease (3)
1- upper lobe infiltrates
2- lung volume loss
3- +/- cavitation
why is CXR alone not diagnostic for active TB (1)
1- because CXR findings by themselves are not specific to TB, and therefore the test has low specificity (spIN)
how many samples should be collected for AFB smear and culture? (1)
1- at least 3 sputum samples (induced or spontaneous)
when, and how far apart should samples should be collected for AFB smear and culture? (2)
1- collect all samples on the same day to improve convenience for patients
2- collect samples minimum of 1 hour apart
what kind of sample concentration should lab testing for AFB smear microscopy be done (1)
1- testing should be done on concentrated samples
what kind of microscopy should be done for AFB smear (1)
1- fluorescent microscopy, to maximize sensitivity
when should sputum TB mycobacterial culture be performed (1)
1- with every sputum sample, alongside AFB smear
how long does it take for TB mycobacterial culture results to arrive (1)
1- 2-8 weeks
how does nucleic acid amplification tests (NAAT) results compare with TB culture results in terms of turnaround time (1)
1- NAAT results are much faster than conventional culture
is NAAT as a test highly sensitive or specific, and in what case (3)
1- sensitive
2- NAAT is more sensitive in smear-positive samples
3- negative NAAT alone should not be used to r/o TB disease
how often should NAAT be done as part of active TB diagnosis (1)
1- at least one AFB+ respiratory sample should have NAAT done on it, in all new smear-positive patients
On what kind of culture sample should phenotypic (culture) drug susceptibility testing be done as part of active TB diagnosis? (1)
1- phenotypic DST should be done routinely for all first-positive-culture isolates obtained from a new TB case
what tests are NOT recommended for diagnosing active TB disease (3)
1- IGRA
2- TST
3- serologic antibody-based tests
what are the 2 recommended regimens for treating LTBI, i.e. tuberculosis preventive treatment (TPT) (2)
1- 3HP - once-weekly rifapentine + isoniazid for 3 months, OR
2- 4R - daily rifampin for 4 months
what is the difference in administration of the first-line treatments for LTBI, 3HP and 4R (2)
1- 3HP needs to be directly observed (DOT)
2- 4R can be self-administered and not DOT
is rifapentine licensed for use in TPT for LTBI in Canada? (1)
1- currently no; however it is on the ‘list of drugs for an urgent public health need’
what is the second-line TPT regimen in Canada (1)
1- 9H - daily isoniazid for 9 months (take Vit B6 with each dose to prevent neuropathy)
if a patient with LTBI takes other medications, what needs to be considered before starting TPT (1)
1- interactions between patients’ baseline medications and TPT meds must be considered
TPT meds do have s/e; what must be considered in the patient-provider shared decision-making process in terms of starting TPT vs. not (1)
1- decision to use TPT should consider risk of tuberculosis preventive therapy (TPT) vs. risk of developing active TB disease
can you use TPT in active TB disease (1)
1- NO - active TB disease must be excluded to use TPT
what are alternative TPT regimens in Canada after 3HP, 4R and 9H (3)
1- 6H - daily isoniazid for 6 months
2- intermittent - twice-weekly isoniazid for 9 months
3- 3HR - daily isoniazid and rifampin for 3 months
can pregnant patients receive TPT for LTBI? (1)
1- generally TPT should be deferred till after delivery, unless risk of TB reactivation is high
If TPT is indicated, can the both first-line regimens for TPT be used during pregnancy? (2)
1- NO. Only recommended to use 4R (daily rifampin for 4 months)
2- 3HP (once-weekly isoniazid + rifapentine for 3 months) should be avoided
how long should isoniazid-based TPT regimens be avoided in a pregnant person (1)
1- should avoid isoniazid-based TPT until 3 months postpartum
if a pregnant person is a contact of a rifampin-resistant TB case and has a high reactivation risk, what is the TPT regimen option (1)
1- in this highly exceptional circumstance, isoniazid-based TPT can be an option
TPT is given when there is a risk of conversion from LTBI to active disease.
What are very high risk factors for conversion to active TB? (4)
1- HIV/AIDS
2- child <18yo with recent TB exposure (contact)
3- adult >18yo with recent TB exposure (contact)
4- silicosis
TPT is given when there is a risk of conversion from LTBI to active disease.
What are high risk factors for conversion to active TB? (5)
1- Stage 4/5 chronic kidney disease with or w/o dialysis
2- all transplant recipients
3- fibronodular disease
4- receiving immunosupressive drugs (e.g. TNF alpha inhibitors, steroids)
5- certain cancers
TPT is given when there is a risk of conversion from LTBI to active disease.
What are moderate risk factors for conversion to active TB? (4)
1- granuloma on CXR
2- diabetes
3- heavy alcohol use (3+ drinks/d)
4- heavy tobacco use (at least 1 pack/d)
TPT is given when there is a risk of conversion from LTBI to active disease.
Who is at low risk for conversion to active TB? (2)
1- general (adult) population with no known risk factors
2- positive two-step TST booster and no known risk factor
what is directly observed treatment (DOT) for TB (1)
1- Comprehensive, patient-centred care to ensure 100% of prescribed doses are taken
in what setting is DOT recommended to be based out of as per 8e Canadian TB stds (1)
1- community-based DOT (as opposed to clinic-based DOT)
what are some potential indicators of TB treatment non-adherence that might necessitate DOT
(‘medical’- 3’
‘SDoH’- 2
‘host factors/behaviour’- 2)
(7)
1- Disease due to multidrug-resistant organisms
2- Major mental illnesses
3- Treatment failure or disease relapse
4- Injection drug use/other substance use
5- Homelessness or unstable housing
6- Previous non-adherence
7- Children and adolescent cases
how many phases is treatment for active TB given in (2)
1- two phases
2- intensive phase and continuation phase
what are the 4 objectives for treating active TB disease (4)
1- rapid killing of TB bacilli (bactericidal)
2- prevent emerging/worsening drug resistance
3- prevent relapse of disease
4- optimize long-term health with comprehensive care - linkage to services, mitigating social/econ vulnerabilities
in the intensive phase of TB treatment, how many drugs are used and why (2)
1- 3-4 drugs are used, guided by drug susceptibility testing (DST) results
2- in order to rapidly kill TB organisms and prevent the selection of drug-resistant organisms
what are the 4 drugs used to treat active TB in intensive phase - RIPE (4)
1- rifampin
2- isoniazid (+ pyridoxine to prevent neuropathy)
3- pyrazinamide
4- ethambutol
how long should the intensive phase of active TB treatment last in drug-susceptible disease (1)
1- two (2) months
during the intensive phase of active TB treatment, how often should drugs be dosed (1)
1- daily (no intermittent option)
is there a daily maximum dose for rifampin (1)
1- NO (this is a change in the 8e Canadian TB stds)
how long is the continuation phase for treatment of active TB? (1abc, 2)
1- duration varies based on:
1a- drug regimen
1b- adherence
1c- risk of relapse
2- typically 4 months
in the continuation phase for treatment of active TB, how many drugs are used (1a), how often are they dosed (1b), and what is a c/i to the first dosing option (1c)
1a- minimum 2 drugs
1b- intermittent (thrice-weekly) under DOT option can be done, but daily is preferred
1c- intermittent dosing is c/i in those with HIV
briefly describe rifampin (RMP) (active TB treatment) (4)
1- most important anti-TB drug
2- has good bactericidal activity
3- prevents acquired drug resistance
4- important in preventing disease relapse
briefly describe isoniazid (INH) (active TB treatment) (3)
1- powerful bactericidal activity
2- effective in preventing emergence of resistance
3- peripheral neuropathy is common s/e so pyridoxine (Vit B6) is routinely added
briefly describe pyrazinamide (PZA) (active TB treatment) (2)
1- bactericidal
2- only of benefit in first 2 months
briefly describe ethambutol (EMB) (active TB treatment) (4)
1- least bactericidal
2- least effective in preventing relapse
3- but effectively prevents drug resistance
4- can be discontinued in continuation phase if DST fully susceptible to all first-line drugs
what is the total duration of standard active TB treatment regimen in drug-susceptible cases (intensive + continuation phases) (1)
1- standard duration is 6 months - 2 (intensive) + 4 (continuation)
what is the preferred treatment regimen for suspected drug-susceptible active TB (2)
1- INH + RMP + PZA + EMB daily (intensive phase, first 2 months) - RIPE
2- INH + RMP + EMB daily (continuation phase, 4 months) - RIE
what is the preferred treatment regimen for known drug-susceptible active TB (2)
1- INH + RMP + PZA daily (intensive phase, first 2 months) - RIP
2- INH + RMP daily (continuation phase, 4 months) - RI
*EMB can be discontinued
