149) A 29 year old internal medicine resident physician has been exposed to a patient with cavitary pulmonary tuberculosis 1 month ago. He denies any symptoms. His physical examination is normal. A tuberculin skin test reaction is positive now at 6mm. His Skin test one year ago was negative. A chest X-ray is within normal limits and chemistry panel is normal. The most appropriate management optiuon for this patient is :
A) Isoniazid, Pyrazinamide, Rifampin and Ethambutol for 9 months
B) Observation as ≥ 10mm is considered positive in health care workers
C) Isoniazid for 9 months
D) Rifampin for 9 months
E) Isoniazid for 6 months
Archer USMLE Step 3 Blog 
b?
c
B
would it be B since it is 10 to be considered ppd positive
its B
B
Isonized 9 months.
bbb
C
The correct answer is “C”. Key word: Exposed to an individual with TB, suggests the guy needs INH with B6.
No this pt is exposed but not a close contact of index pt hence the cut off threshold of induration is 10mm , he has only 6 mm induration Hence not RX him
Recent contact of infectious TB disease (like this resident) is considered positive with greater than 5 mm induration. He does not have to be a close contact to meet the criteria.
http://www.cdc.gov/tb/publications/LTBI/diagnosis.htm
It is inh for 9months it is positive>5mm
USPSFT followes CDC 2006 ‘Guideline for investigation of contacts of person with Infectious TB’.
Source(patient)- has infectious TB (equal to cavitary lesion or positive AFB or positive gastric aspirate)
Contact(resident doctor)- has PPD 6mm induration.
CDC interprets an induration transverse diameter of >5mm as positive in ANY contact (casual or close) of INFECTIOUS TB.
(www.cdc.gov/mmwr/preview/mmwrhtml/rr5415a1.htm
read under section ‘diagnostic and public health evaluation of contacts, subsection – tuberculin skin testing
This doctor was exposed to an infectious case of TB and he is declared positive by CDC and USPSTF standards. The most appropriate management for this patient is to start INH daily for 9 months. (C)
If this doctor was not exposed to an INFECTIOUS case of TB, he would have been a contact with low priority risk and an induration of >10mm would be considered positive.
Question is, who must have LTBI prophylaxis at > 5mm induration?
1. Immunosuppressed patients (by disease or by cytotoxic or even >15mg prednisone or equivalent for >4weeks) -high risk group
2. Contacts of Infectious TB case (all)
3. Evidence of previous TB on CXR (fibrotic changes)
Then who should have LTBI prophylaxis at >10mm induration?
1. ALL ADULTS AND CHILDREN WITH NORMAL IMMUNE SYSTEM + NO EXPOSURE HISTORY TO ACTIVE (INFECTIOUS)TB, HOWEVER, THEY HAVE BEEN EXPOSED TO SOME FORM OF TB
LOWER RISK TB EXPOSURE – examples include individuals exposed to confirmed NON infectious TB or TB on treatment in which AFB is negative or no specific traceable infectious source LIKE BEING IN HIGH RISK AREAS OR GEOGRAPHICAL ZONES. All these individuals have good immune system but they have been exposed to some form of form of TB THAT HAS NOT been proven to be active. They have no confirmed active TB contact.
Who receives LTBI prophylaxis at even zero mm induration?
This is like saying that you do not believe a negative result of PPD. When can you do that? When the exposure occured in a period that is less than 8 to 10 weeks. Clinical suspicion is used to salvage high risk vulnerable patients. Who are the patients we can not risk or afford a false negative test.
Symptomatic children <5years old and immunocompromised Adults
Why? Studies have shown that they are at high risk of rapid diseminated form of TB that is also lethal.
1. Children1wk, and you have clinical suspicion of TB, initiate PTBI prophylaxis with INH daily or Rifampicin until repeat PPD in 8 to 10 weeks. If it is negative then, prophylaxis can be stopped.
2. Immunocompromised individuals (Low CD4 count), exposed to high risk individuals (one with active confirmed TB), and there is clinincal suspicion of TB, initiate PTBI prophylaxis. If repeat PPD is positive after window period, LTBI prophylaxis is continued
3. Severely immunocompromised individuals exposed to active TB
Key words Clinical suspicion, PPD reads negative, risk group vulnerable to rapid disemminated TB (immunosuppressed or children<5years),if untreated for next 10 weeks.
FOR RECALL(IN EXAM):
a,if you hear or feel the word 'confirmed ACTIVE' or 'confirmed IMMUNODEFICIENCY' – it's 5mm for positive NOT found?, look at b,
b,If you hear 'confirmed' RISK ALONE – it's 10mm for positive
c,If you hear SYMPTOMATIC CHILD 12 years.- INH plus Rifapentine RPT once weekly dose for 12 weeks in age >12 years and adults
FOR RECALL (IN EXAM):
c, …(cont’d) if you hear SYMPTOMATIC CHILD 12 years and adults is an alternative to 9 months of once daily INH prophylaxis. (recommended by CDC)
something is omitted from my post twice. I think there is a misunderstanding or error somewhere. Between Symptomatic child and 12 years there is a note. What I want to say is that if a child <5 years has features giving you high clinical suspicion but PPD is negative and you are in the window period of PPD test (8-10 weeks), give INH prophylaxis. Same goes also for immunocompromised patients with low CD 4 count. HIGH SUSPICION, PPD negative, Contact less than 8 to 10 weeks ago, start PPD.
I mean, … start INH Prophylaxis. After, 8 to 10 weeks repeat PPD testing, if it is positive, continue INH. otherwise, stop
B according to MTB book of 2012.
I also think B. High risk is close contact to active TB. Duration of contact with patient and health care personal and duration of contact with family members and patient is different. I think B is correct.
C. This resident was a close contact for 1 month. > 5 mm : needs INH x 9 months.
Summary:
NO RISK – > 15 mm is positive (employment health check incidental discovery)
LOW RISK – > 10 mm is positive (Not exposed to active TB including incidental discovery) LOW RISK for progression to active disease.
HIGH RISK – > 5 mm is positive (Exposed to active TB)
VERY HIGH RISK – < 5mm is positive ('exposed' child < 5 year old, or severely immunocompromised patient), meaning progression is extremely likely.
INDETERMINATE RISK – do T-Spot TB test, result comes out in 24 hours. Still indeterminate, then do IGRA (Interferon Gamma Release Assay) specifically Quantiferon TB Gold-in-Tube test QFT-GIT.
This patient was exposed to active TB = High Risk; hence he's positive at greater than 5 mm induration. My Answer is Option C.
REFERENCES:
1. Guidelines for the investigation of Contacts of Persons with Infectious TB – http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5415a1.htm
2. Diagnosis of Latent TB Infection – http://www.cdc.gov/tb/publications/LTBI/diagnosis.htm
3. Updated Guidelines for using Interferon Gamma release Assays to detect Mycobacterium tuberculosis Infection – United States 2010 – http://www.cdc.gov/mmwr/pdf/rr/rr5905.pdf