The diagnosis of active TB

The diagnosis of active TB

Faculty/Presenter Disclosure Faculty: Martha Ainslie Relationships with commercial interests: Speakers Bureau/Honoraria: Boehringer Ingelheim

Mitigating Potential Bias I have received no commercial support from any company that has commercial interests in the diagnosis or treatment of tuberculosis.

Who cares about active TB?

Current status of TB in FN and Inuit TB rates in 2014 Inuit: 198/100 000 FN on reserve: 20/100 000 (incidence ranged from 26-106/100 000 from 2000-2012 in Northern Manitoba) FN off reserve: 15/100 000 Metis: 3/ 100 000 Canadian others: 4/100 000

Definition of active TB MTB complex= M TB M Bovis M africanum M Canetti Positive culture or significant evidence of disease with compatible xray changes, pathology or post mortem evidence of infection, or clinically active non-respiratory TB

In order to develop active TB you must have been Exposed to a patient with infectious TB (respiratory or laryngeal) You have to inhale the TB bacilli and become infected You are unable to contain the infection and get progressive primary disease or the infection becomes active several months to years after the initial infection ( most common scenario)

Probability of Transmission Infectiousness of person with TB Number of infectious particles produced Environment in which exposure occurred Air circulation UV light exposure Duration of exposure Virulence of the organism

Infectiousness of Patient with TB Number of particles produced Smear positive or negative Extent of disease Type of disease (laryngeal TB) Cavity (increases the number of particles by 5-6 logs)

Canadian Tuberculosis Standards 2000

Diagnosing active tuberculosis Think about 1. Are the patient s symptoms suggestive of TB 2. What is the probability that the patient has been exposed to a person with active respiratory TB? 3. Does the patient s have underlying medical issues that will predispose them to developing active TB? 4. What does the CXR show?

Signs and symptoms Insidious Symptoms present for weeks to months Pulmonary symptoms absent in 30% who only have constitutional symptoms Dyspnea seen in < 50% of patients Exam is often normal

Think about TB Cough>3 weeks and Weight loss Night sweats Fever>2 weeks Hemoptysis Fatigue Failure to improve with a course of antibiotics Unexplained weight loss

Pre test probability What is the likelihood that this person has been exposed to an infectious case of TB in their lifetime? Lived in First Nations community Immigrant from country with high prevalence of TB (don t forget the Canadian born children) Travel to a country with high prevalence Incarceration, homelessness, intravenous drug use Health care worker Close contact of an infectious case

Canadian Tuberculosis Standards 2013

CXR in the diagnosis of active TB Typical findings 90% have infiltrate in apicoposterior segment of UL or superior segments of LL Loss of volume Cavitation: seen in later stage and in patients with vigorous immune system. Often not seen in patients who are immunocomprimised

Limitations of CXR Atypical features on CXR are seen in patients with HIV, renal failure, diabetes, solid organ transplant or on chronic steroids CXR may not show cavitation May have a LL or RML infiltrate May have hilar or mediastinal adenopathy (especially in HIV patients) If any CXR abnormality is considered the sensitivity of the CXR is 95% HIV patients or patients who are close contacts to an infectious case can have a normal CXR

What to do when you suspect TB?

If you suspect pulmonary TB N95 mask if you are about to see the patient Get sputum as a first step Isolation Tell the patient to stay at home until you have made some phone calls The patient may be eligible for home isolation Contact your local TB team for advice on how to proceed Phone HSC and ask to speak to the respirologist taking outside calls Talk to ID specialist on call

Sputum Sputum for AFB and culture 3 sputa, can be collected on the same day at least 1 hour apart. Each sputum sample should be 5 ml Deliver to lab within 1 hour, if patient can t then refrigerate and protect from light AFB staining Rapid In pulmonary TB a single smear has a sensitivity of 60% Need an estimated 10 000 organisms per ml to be smear positive, need only 10-100 organisms to have a positive culture Not all that is AFB + is TB. NAAT to confirm on Smear + cases Negative smears do not rule out TB Must await cultures which can take 6 weeks If we have a high pre-test probability we may start therapy while awaiting cultures

Pulmonary TB samples Yields on samples Sputum expectorated/induced (90%) Bronchoscopy (70%) Gastric aspirates (70%) Smear and culture assessment Smear positive (5,000 to 10,000 Bacteria/ml) Culture positive (10-100 Bacteria/ml)

TST and TB disease in adults TST used to diagnose prior infection and not disease. A negative test does not rule out TB disease and a positive test does not rule in prior TB infection. TST will be negative in 20-30% of patients with active disease. Do NOT use to diagnose TB disease in adults

Summary Determine the pre-test probability that the patient has come into close contact with an infectious case of TB over their lifetime Does the patient have medical issues that would increase the risk of reactivation? If you are concerned about possible TB order a CXR Always consider in UL airspace disease especially if it is cavitated or in a nonresolving pneumonia Obtain sputum for AFB x 3. Can be collected on the same day If you get a positive AFB smear or culture or have a suspicious CXR then call your local TB expert