Bureau of Tuberculosis Control

Tuberculosis Surveillance of Health Care Workers: Tuberculin Skin Testing

TB Fact Sheet 5b

In health care facilities, certain health care workers (HCWs) may become infected with Mycobacterium tuberculosis through repeated exposure to patients with tuberculosis (TB) disease. In addition to infection control measures (e.g., early identification and isolation of patients likely to have infectious TB, engineering controls), control of TB transmission in health care facilities includes TB surveillance among employees. Timely detection of TB infection in a HCW not only permits the individual to begin treatment of latent TB infection (LTBI) but also may indicate the need to initiate further investigation and reassessment of the facility's infection control system.

Who should be screened?

HCWs who are assessed to be at risk for exposure to TB should be screened periodically with the tuberculin skin test (TST) by the Mantoux method unless they have documentation of a positive result on a previous TST. These HCWs should undergo pre-employment skin testing (preferably two-step) in order to establish a baseline result. HCWs at high risk of exposure include all part-time and full-time workers, paid or unpaid, who do any of the following:

• • Care for or are in contact with patients with known or suspected TB disease
• • Perform autopsies
• • Handle laboratory specimens that may contain Mycobacterium tuberculosis
• • Work in correctional facilities and homeless shelters

The TST can be performed safely and reliably even when the employee is pregnant. Unless a prior positive TST has been documented, HCWs who have received the bacille Calmette-Guérin (BCG) vaccine should also be skin-tested.

Frequency of TST screening

According to CDC guidelines, the frequency of TST screening in a health care facility should be based on the following:

• • The profile of TB in the community
• • The number of patients with infectious TB to whom the HCWs in an area or occupational group may be exposed
• • Previous documentation of person-to-person transmission of M. tuberculosis and HCW skin test conversions (if any)

HCWs who are potentially at high risk for exposure to TB should be tested every 6 months; others may be tested annually.

Administering the TST

Tuberculin skin testing should be provided at a time and place convenient for HCWs. Voluntary testing should also be available at other times. Staff who administer the TST should be trained to perform Mantoux skin tests according to CDC standards; their performance should be periodically evaluated for quality assurance. In addition, they should be trained to collect relevant information on factors that can influence the TST result, including any history of BCG vaccination, community or work exposure to TB, immunosuppressive therapy or medications (e.g., corticosteroids), and weight loss greater than 10% of ideal body weight.

Interpreting TST results

The TST reaction should be read only by a trained health worker. Generally, an induration of 10 mm is considered to be significant in a HCW; however, an induration as small as 5 mm may be significant in certain situations - such as known exposure to TB - while the induration must measure at least 15 mm to be considered significant when the likelihood of exposure is very low. TST conversion is defined as an increase of at least 10 mm in induration (if the result was < or = 10 mm on a previous TST). For example, if a person's previous TST result was 7 mm, a documented conversion would be a TST result measuring > or = 17 mm.

Follow-up for significant TST results

If a HCW has a significant TST result at initial screening, or if an employee's TST converts from negative to positive, it is important to do the following:

• • Provide counseling concerning latent TB infection, treatment of LTBI, and signs and symptoms of TB disease
• • Make arrangements for the employee to receive a chest radiograph (CXR) and medical evaluation and, if indicated, to start treatment of LTBI

If the CXR at the initial evaluation is normal, periodic follow-up CXRs are not recommended. (See TB Fact Sheet 1d: The Chest Radiograph Following a Positive Tuberculin Skin Test.) However, all TST-positive HCWs should be counseled periodically about the signs and symptoms of TB and the need for prompt evaluation of any symptoms suggestive of TB.

Reporting results

An individual's TST result is confidential and should be provided to that individual only. According to regulations of the Public Employee Safety and Health Bureau (PESH) regulations of the New York State Department of Labor, each year, throughout the month of February, the employer must post information for each work location on the number of skin test conversions and the job titles of converters (without revealing names).

Epidemiologic investigations

The TST results for HCWs in each work location should be reviewed. Further investigation is warranted when TST conversion from negative to positive is documented in an employee whose history does not identify a probable source of infection outside the facility. A contact investigation is warranted if a likely source patient is identified within the facility or if the HCW is diagnosed with active TB.

Notes and References

1. Centers for Disease Control and Prevention. Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care facilities, 1994. MMWR 1994;43(No. RR-13):8-18,42-43.

For further information, call 311.