Standard Tuberculosis Screening Protocols

Purpose

To identify healthcare workers with Mycobacterium Tuberculosis (M. Tuberculosis)

Scope

Healthcare workers include employees, volunteers, students and special purpose trainees, who have broadly defined patient care duties.  Testing is done at pre-placement, annually, after exposure to a person with infectious tuberculosis, for symptoms suggestive of TB.

Rationale

Identification of infected individuals is essential for the control of tuberculosis within the healthcare environment.  Testing is done on an annual basis in order to (1) identify converters who are at risk for developing disease and (2) monitor the effectiveness of the institutional TB control program.  The preferred skin test for M. Tuberculosis infection is the intradermal, or Mantoux method.  It is administered by injecting 0.1ml of 5 tuberculin units (TU) PPD intradermally into the dorsal or volar surface of the forearm.  An Interferon Gamma Release Assay (IGRA) in vitro (blood) test can also be used to diagnose TB infection at the discretion of OHS staff (see IGRA TB Blood test document).

Procedure

  1. All healthcare workers who do not have a history of a reactive skin test or positive blood test must be must be tested annually as a condition of employment in the health system. TB testing may not be administered earlier than 30 days of annual due date.
  2. Apply Mantoux skin test by injecting 0.1ml intradermally of PPD tuberculin containing 5 tuberculin units into the volar upper surface of the forearm, carefully avoiding any veins.  The injection should be made with a safety disposable tuberculin syringe, with the needle bevel facing upward, producing an elevation of the skin 6 mm to 10 mm in diameter.
  3. The safety device must be activated after injection and the syringe discarded in a puncture resistant container for disposal.  Gloves are not necessary for this procedure.
  4. If the healthcare worker gives a history for conditions that might predispose to anergy, such as HIV infection, immunosuppressive therapy or other immunodeficiency states, an IGRA blood test should be drawn. 
  5. The Mantoux skin test must be read 48 to 72 hours after the injection by a qualified* individual other than the employee undergoing testing.  The reading should be based on measurement of induration, not erythema.  Diameter of induration should be measured transversely to the long axis of the forearm and recorded in millimeters.  The reaction to intracutaneously injected tuberculin is a delayed-type (cellular) hypersensitivity (DTH) reaction, and infection by M. tuberculosis usually results in a DTH response to PPD tuberculin that is detectable 2 – 12 weeks after infection.  Delayed hypersensitivity reactions to tuberculin usually begin 5 – 6 hours after injection, reach a maximum at 48 to 72 hours, and subside over a period of a few days, although positive reactions often persist for up to one week.
  6. Skin-test reactive persons will be evaluated for active disease and an IGRA TB blood test may be ordered.  If the blood test is negative this individual will be tested annually by IGRA.
  7. Individuals with positive blood test results will be seen by a clinician for a latent TB assessment.  A chest x-ray will be ordered and they will need to schedule an appointment to review recommendations for prophylactic treatment of latent tuberculosis infection. These individuals will be required to complete an annual symptom review questionnaire.
  8. MMR vaccine may interfere with the response to a tuberculin test.  There is currently no information on the effect of Varicella vaccine on reactivity to a tuberculin skin test (PPD). Live measles vaccine given prior to the application of a PPD can reduce the reactivity of the skin test because of mild suppression of the immune system.  Until information is available, it is prudent to apply the same rules to Varicella vaccine as are applied to MMR.  A PPD can be applied before or on the same day that MMR or Varicella vaccine are given.  However, if MMR or Varicella vaccine is given on the previous day or earlier, the PPD should be delayed for at least one month.  

Interpretation of the Mantoux Skin Test

Purpose

The purpose of this protocol is to establish a consistent method for the interpretation of Mantoux skin tests administered by the UM Occupational Health Services (UM OHS).

Scope

This protocol will apply to all skin tests administered in or under the auspices of the UM Occupational Health Services (UM-OHS).

Rationale

The interpretation of a PPD reaction should be based on the purpose for which the test is given, the prevalence of TB infection in the population being tested, and the consequences of inaccurate classification.  The likelihood that a person with a positive PPD is actually infected with M. Tuberculosis is dependent upon the prevalence of tuberculosis in the population group to which the person belongs.  This forms the basis for the different cut points used to classify a skin test as positive.

Procedure

  1. All skin tests will be interpreted by this protocol as being negative based on a reading at 48 to 72 hours by a qualified* individual other than the employee undergoing testing.  A skin test may be read as positive based on a reading up to five days after administration of the test. 
  2. Based on the sensitivity and specificity of the tuberculin skin test and the prevalence of TB in different groups, three cut-off levels have been recommended for defining positive tuberculin reactions:  ³5mm,  ³10mm,  and ³15 mm of induration.
  3. For persons who are at highest risk for developing TB disease if they become infected with M. Tuberculosis, a cut-off level of  ³5mm is recommended.  A tuberculin reaction of 5 mm or more is classified as positive in the following groups:
    • Persons with HIV infection or risk factors for HIV infection with unknown HIV status
    • Persons who have had recent close contact with tuberculosis case patients
    • Fibrotic changes on chest radiograph consistent with prior TB
    • Patients with organ transplants and other immunosuppressed patients (receiving the equivalent of >15mg/d of prednisone for 1 month or more)
  4. A reaction of  ³10mm induration should be considered positive for those persons with an increased probability of recent infection or with other clinical conditions that increase the risk for TB (e.g., recent immigrants from high prevalence countries and injection drug users).  In addition to the groups listed, high prevalence populations identified by analysis of local epidemiological data should be targeted for testing.  A tuberculin reaction of 10 mm or more is classified as positive in persons who do not meet the above criteria but who have other risk factors for tuberculosis.  These include:
    • Recent immigrants (i.e., within the last 5 years) from high prevalence countries
    • Injection drug users
    • Residents and employees’ of the following high risk congregate settings:  prisons and jails, nursing homes and other long-term facilities for the elderly, hospitals, and other healthcare facilities, residential facilities for patients with acquired immunodeficiency syndrome (AIDS), and homeless shelters
    • Mycobacteriology laboratory personnel
    • Persons with the following clinical conditions that place them at high risk:  silicosis, diabetes mellitus, chronic renal failure, some hematologic disorders (e.g., leukemias and lymphomas), other specific malignancies (e.g., carcinoma of the head or neck or lung), weight loss of >10% of ideal body weight, gastrectomy, and jejunoileal bypass
    • Children younger than 4 years of age or infants, children, and adolescents exposed to adults at high risk
  5. Routine tuberculin skin testing is not recommended for populations at low risk for Latent Tuberculosis Infection.  However if these persons are tested (e.g., at entry into a worksite where risk for exposure to TB is anticipated and a longitudinal tuberculin testing program is in place), a higher cut-off of  ³15 mm is recommended.  A reaction of 15 mm or more is classified as positive for persons who do not meet any of the above criteria.
    • Persons with no risk factors for TB
  6. Skin test conversions.  For persons with negative skin test reactions who undergo repeat skin testing (e.g., health care workers), an increase in reaction size of >10 mm within a 2 year period should be considered a skin test conversion indicative of recent infection with M. tuberculosis.
  7. Previous vaccination with BCG.  IGRA TB blood testing is recommended for persons vaccinated with BCG, though tuberculin skin testing is not contraindicated.  The skin test results of such persons can be used to support or exclude the diagnosis of M. tuberculosis infection.  No method can reliably distinguish tuberculin reactions caused by vaccination with BCG from those caused by natural mycobacterial infections.  A positive reaction to tuberculin in BCG-vaccinated persons indicates infection with M. tuberculosis when the person tested is at increased risk for recent infection or has medical conditions that increase the risk for disease.

MANTOUX TESTING TWO-STEP PROTOCOL

Purpose

To reduce the likelihood of interpreting a boosted reaction as representing a recent infection.

Scope

Two-step baseline PPD testing will be required for all new employees/volunteers/students who have not been skin tested in the previous year.

Rationale

Boosted reactions occur in people who have been infected with any species of mycobacterium or by past BCG vaccination.  These persons develop a hypersensitivity to tuberculin which may gradually wane over the years. When skin tested at this point, these persons may have reactions that are negative.  However, the stimulus of this skin test may recall the hypersensitivity, which results in an increase in the size of the reaction to a subsequent test.  This may falsely be interpreted as a recent conversion from negative to positive. 

Procedure

  1. Apply Mantoux test according to skin testing protocol.
  2. Instruct the employee/volunteer to evaluate their TB test in 48-72 hours.  If a raised reddened area is noted they should return to OHS.  If the reaction is positive according to OHS protocol, two step testing is not necessary and employee is evaluated according to OHS protocols.  If the area remains flat they are to return to OHS in one week.
  3. At the one week visit, the Mantoux test will be reapplied according to skin testing protocol.
  4. The test will be read by a qualified* individual other than the employee undergoing testing and documented according to the protocol for interpretation of the Mantoux skin test 48 to 72 hours after the skin test has been applied.
  5. If second test is positive, the person is considered to have “boosted” which is indicative of past conversion.  Employee will be evaluated according to OHS protocol for positive TB skin test.  If the second test is negative, employee may be entered into the annual TB skin testing program.
  6. The IGRA TB blood test can be used in place of PPD if boosting is considered likely.  (see IGRA TB Blood test document)

*Qualified individual requirements determined by OHS staff.