Can you test positive for TB but not have it?

 Can you test positive for TB but not have it?

Persons with latent TB infection (LTBI) do not feel sick and do not have any symptoms, but usually have a positive reaction to the tuberculin skin test or TB blood test. They are infected with TB bacteria, but do not have TB disease. Persons with LTBI are not infectious and cannot spread TB infection to others.

Will latent TB show up on xray?

Will latent TB show up on xray?

Image result for quantiferon gold positive but negative chest x-ray

Chest Radiograph

Lesions may appear anywhere in the lungs and may differ in size, shape, density, and cavitation. These abnormalities may suggest TB, but cannot be used to definitively diagnose TB.Apr 18, 2016

What can cause a false positive QuantiFERON gold?

 What can cause a false positive QuantiFERON gold?

(1) False-positive results may occur in patients with prior infection with M marinum, M szulgai, or M kansasii. Negative: No IFN-gamma response to M tuberculosis antigens was detected

You Could Have TB

 A person has latent TB infection if they have a positive TB skin test and a normal (negative) chest x-ray. This means the person has breathed in the TB germs, but his or her body has been able to fight the germs. People with latent TB infection do not feel sick and do not have signs of TB disease.

copy from https://www.cdc.gov/tb/topic/infectioncontrol/TBhealthCareSettings.htm 

TB Infection Control in Health Care Settings

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A tuberculosis (TB) infection control plan is part of a general infection control program designed to ensure the following:

• prompt detection of infectious TB patients,
• airborne precautions, and
• treatment of people who have suspected or confirmed TB disease.

In all health care settings, particularly those in which people are at high risk for exposure to TB, policies and procedures for TB control should be developed, reviewed periodically, and evaluated for effectiveness to determine the actions necessary to minimize the risk for transmission of TB.

The TB infection control program should be based on a three-level hierarchy of control measures and include:

1. Administrative measures
2. Environmental controls
3. Use of respiratory protective equipment

On May 17, 2019, the Centers for Disease Control and Prevention (CDC) and the National Tuberculosis Controllers Associationexternal icon (NTCA) released updated recommendations on the frequency of TB screening, testing, and treatment for health care personnel.  For guidance on facility risk assessments and infection control practices please continue to refer to the Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005.

• Administrative Measures
• Environmental Controls
• Respiratory Protective Equipment

Administrative controls are the first and most important level of the hierarchy.  These are management measures that are intended to reduce the risk or exposure to persons with infectious TB.  These control measures consist of the following activities:

• Assigning someone the responsibility for TB infection control in the health care setting;
• Conducting a TB risk assessment of the setting;
• Developing and implementing a written TB infection-control plan;
• Ensuring the availability of recommended laboratory processing, testing, and reporting of results;
• Implementing effective work practices for managing patients who may have TB disease;
• Ensuring proper cleaning, sterilization, or disinfection of equipment that might be contaminated (e.g., endoscopes);
• Educating, training, and counseling health care personnel, patients, and visitors about TB infection and TB disease;
• Screening, testing, and evaluating personnel who are at risk for exposure to TB disease;
• Applying epidemiology-based prevention principles, including the use of setting-related TB infection-control data;
• Using posters and signs to remind patients and staff of proper cough etiquette (covering mouth when coughing) and respiratory hygiene; and
• Coordinating efforts between local or state health departments and high-risk health-care and congregate settings.

Page last reviewed: May 14, 2019

Content source: Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention

Why does BCG vaccine cause false-positive TB test?

Testing in BCG-Vaccinated Persons

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Many people born outside of the United States have been given a vaccine called BCG.

People who were previously vaccinated with BCG may receive a TB skin test to test for TB infection. Vaccination with BCG may cause a false positive reaction to a TB skin test. 

A positive reaction to a TB skin test may be due to the BCG vaccine itself or due to infection with TB bacteria.

TB blood tests (IGRAs), unlike the TB skin test, are not affected by prior BCG vaccination and are not expected to give a false-positive result in people who have received BCG. 

Can latent TB cause damage?

The bacteria are still in your body, but they are not causing damage. However, latent TB bacteria can 'wake up' and become active in the future, making you ill. This can happen many years after you first breathe in TB bacteria.

What causes latent TB to become active?

TB bacteria become active if the immune system can't stop them from growing. When TB bacteria are active (multiplying in your body), this is called TB disease. People with TB disease are sick. They may also be able to spread the bacteria to people they spend time with every day.

TB blood tests are the preferred method of TB testing for people who have received the BCG vaccine. 

Why does BCG vaccine cause false-positive TB test?

Background: Bacille Calmette-Guérin (BCG) vaccination is known to cause false-positive tuberculin skin test (TST) results from cross-reactions with mycobacterial antigens. However, the duration of BCG vaccination influence on the TST is poorly characterized.

Information from the baseline individual TB risk assessment  should be used to interpret the results of a TB blood test or TB skin test given upon hire (i.e., preplacement). Health care personnel with a positive TB test result should receive a symptom evaluation and a chest x-ray to rule out TB disease. Additional workup may be needed based on those results.

Health care personnel with a documented history of a prior positive TB test should receive a baseline individual TB risk assessment and TB symptom screen upon hire (i.e., preplacement). 

A repeat TB test (e.g., TB blood test or a TB skin test) is not required.

Annual TB testing of health care personnel is not recommended unless there is a known exposure or ongoing transmission at a healthcare facility.

Health care personnel with untreated latent TB infection should receive an annual TB symptom screen. Symptoms for TB disease include any of the following: a cough lasting longer than three weeks, unexplained weight loss, night sweats or a fever, and loss of appetite.

Can TB QuantiFERON be false-positive?

We agree that policies governing screening for latent tuberculosis infection in low-risk populations need to be reexamined and changed. The central finding of our longitudinal study is that false-positive QuantiFERON-TB results predominantly occurred in different individuals in each of the 7 years of the study (1).

If you were vaccinated with BCG, you may test “positive” on a TB skin test. 

This may be due to BCG vaccine, OR to a real TB infection. 

The TB skin test cannot tell the difference. 

A positive skin test, even in a person who has been vaccinated with BCG, usually means latent TB infection.

Treatment of latent TB infection is essential to controlling TB in the United States because it substantially reduces the risk that latent TB infection will progress to TB disease.

Can tuberculosis vaccine give's positive TB test?

Yes you can! The BCG vaccine, or Bacille Calmette Guerin, is routinely given in many countries to protect against TB disease. 

Although there is a chance the BCG vaccine may cause a false-positive TB skin test, this is not likely if you received the vaccine more than 10 years ago.A

How can I tell if I had BCG vaccine?

Our BCG Scar Check Service involves a nurse taking a vaccination history and physically checking the arm for a scar to see whether that person has received the BCG vaccination.

How long does BCG vaccine stay in your system?

The BCG vaccine can take 3 months to provide protection against TB disease. BCG vaccine should ideally be given 3 months prior to travel to a high TB incidence country. The vaccine loses its effectiveness over time, usually within 5 to 15 years.

How long does BCG stay in your system?

Because BCG is a live vaccine, there are some important safety measures to keep in mind that your doctor can explain. BCG can remain in urine for 6 hours after your treatment, so each time you urinate, you should bleach the toilet in your home to neutralize the vaccine.

What causes latent TB to become active?

TB bacteria become active if the immune system can't stop them from growing. When TB bacteria are active (multiplying in your body), this is called TB disease. People with TB disease are sick. They may also be able to spread the bacteria to people they spend time with every day.

Treatment options recommended for LTBI include: 6-month daily isoniazid, or 9 month daily isoniazid, or 3 month weekly rifapentine plus isoniazid, or 3–4 month daily isoniazid plus rifampicin, or 3–4 month daily rifampicin alone. (Strong recommendation, moderate to high quality of evidence.)