Archeological studies reveal tuberculosis has plagued human history in excess of 5,000 years.^1,2 Pre-dynastic Egyptian graves show evidence of the disease through DNA testing as well as spinal deformities in mummies. Pre-Columbian Peruvian mummies 900 years old also indicate the existence of TB in that society.

With the close of the Middle Ages in Europe, clinical study of TB resulted in a growing volume of information regarding tuberculosis, and ultimately, identification of the tuberculosis bacillus in 1882 by Robert Koch. But only in the 1940’s did antibiotic treatment become available, replacing earlier therapy largely centered on isolation and symptomatic management.

Nevertheless, TB remains a significant health hazard, not merely confined to the weak, the poor, and disenfranchised.³ In fact, TB constitutes a challenge to healthcare workers, particularly occupational health clinics that care for employees working in schools, hospitals, other medical clinics, and chronic care facilities where TB remains endemic.

Transmission and Pathogenesis

Tuberculosis is a communicable disease caused by Mycobacterium tuberculosis, the tubercle bacillus. The organism is spread from an individual with infectious TB via tiny airborne particles through inhalation of the droplets. If the inhaled bacilli reach the pulmonary alveoli, they are ingested by macrophages and the organism multiplies.

The TB recipient is considered to have TB infection. Usually the immune system contains the bacilli and the individual remains asymptomatic and is not contagious, although a TB skin test result will be positive.⁴ If, however, the immune system is not able to control the infection, TB disease occurs, and clinical symptoms and physical findings are present. Skin testing is positive and transmission of the disease may follow.

Approximately 10% of those who contract TB infection in the United States will develop TB disease. At-risk individuals include those who are immunosuppressed, IV drug users, persons with HIV, close contacts of patients with TB disease, and healthcare workers exposed to patients with TB disease.

Thus, the challenge is to identify those individuals, referred to as "converters," whose skin test becomes positive due to exposure to TB bacteria, particularly before they develop active disease and transmit the organism to others.

Occupational Healthcare Providers

Occupational healthcare providers deliver an important and necessary service regarding TB testing and management. The Occ Med clinic often provides surveillance for other healthcare workers exposed to patients either with TB or at high risk.

Healthcare workers are presumed to be at elevated risk of developing TB disease compared to the population at large.⁵ For that reason, a variety of federal, state, and local regulations and guidelines ^6,7,8,9 mandate or describe surveillance and periodic testing protocols. Individuals at risk include physician and nursing staff, EMTs and ambulance personnel, teachers, and others. In general, healthcare workers, particularly those in high-risk positions, are required to be tested annually. Others, such as teachers in private or parochial elementary or secondary schools in California, may be tested at least every four years.^10,11

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TB Skin Testing

The Mantoux tuberculin skin test is the standard method of identifying persons infected with M. tuberculosis. The test is performed by a trained and experienced healthcare worker who carefully injects 0.1 ml of purified protein derivative (PPD) tuberculin containing five tuberculin units intradermally into the volar surface of the forearm. The injection is made with a disposable syringe oriented so that the bevel faces upward to produce a discrete, pale elevation of the skin six to 10 mm in diameter. This technique assures an intradermal deposit; an injection below the dermis is not correct procedure.

A properly-trained clinic staff person evaluates the test reaction 48 to 72 hours later. A positive reaction takes the form of a raised and palpable wheal that is measured through the long axis of the forearm; erythema does not constitute a positive reaction. The standard for a positive reaction varies by risk group. A 10 mm or greater reaction is considered positive among the following:

• employees of high-risk congregate settings;

• residents of high-risk congregate settings;

• mycobacteriology laboratory personnel;

• recent arrivals from high-prevalence countries;

• injection drug users;

• children less than four years of age, or children
  and adolescents exposed to adults in high-risk categories.

Among risk groups with impaired response, a reaction of at least 5 mm is considered positive. Individuals in this classification include:

• HIV-positive persons;

• recent contacts of TB cases;

• persons with fibrotic changes on chest x-ray consistent with old, healed TB;

• patients with organ transplants or other immunosuppression factors.

For all other persons with no known risk factors, a reaction of 15 mm or greater is considered positive.^12,13,14

False positive results may arise from nontuberculous mycobacteria or prior administration of BCG vaccine. False negative results may arise from anergy, which occurs with HIV infection, severe or febrile illness, measles or other viral infections, live-virus vaccinations, recent or overwhelming TB disease, Hodgkin’s disease, sarcoidosis, treatment with corticosteroids, or immunosuppressed patients.

Some individuals who were infected with TB many years previously may have a negative reaction to initial TB skin testing. Yet skin testing can boost their response to tuberculin, resulting in positive tests thereafter. On re-testing one to three weeks after the initial TB skin test, these individuals may exhibit a positive reaction, but it should not to be interpreted as a new conversion. This may occur with individuals of any age, although it is more common among older persons. Performing two successive tests is described as two-step testing and is appropriate, even though the initial test was negative, if one suspects that prior TB disease or infection occurred. The American College of Occupational and Environmental Medicine (ACOEM) offers guidelines regarding two-step testing.

"ACOEM fully supports implementation of the Centers for Disease Control and Prevention (CDC)
Guidelines for Preventing the Transmission of Mycobacterium Tuberculosis in Health-Care Facilities, 1994.2,3. In particular, the College endorses the use of individual risk assessments for each clinical facility and its specific components, with review of the institution’s TB-control program at appropriate intervals, in accordance with its case experience. The use of two-step tuberculin testing of newly hired healthcare workers (who have no documentation of a negative purified protein derivative (PPD) test result in the previous 12 months) can avoid pseudoconversions (positive tuberculin reactions due to anamnestic responses, rather than to recent workplace infections)."¹⁵

Treatment of Tuberculosis

The term TB converter is applied when an individual’s test result moves from negative to positive without any extenuating factors as outlined above to explain it. TB treatment should be initiated as soon as a converter is identified. Current disease management guidelines are available from a variety of sources, including the Centers for Disease Control and Prevention and the Morbidity and Mortality Weekly Report.¹⁶ In the Occ Med clinic, a patient with a positive skin test should be evaluated to determine the existence of TB disease, i.e., acute infection. Review of the patient’s medical history and physical examination may reveal the condition. In addition, a chest x-ray should be taken for the clinic physician’s wet reading. If there is clinical evidence of active infection, the patient should be removed from his/her work place until treatment is initiated and the infection is controlled.

In some areas, referral may be made to the County Health Department or a local respiratory medicine specialist. If the Occ Med clinic is familiar and comfortable with managing patients with TB infection, however, then no referral need be made.

Reporting is mandated by several entities. OSHA Standard 29 CFR 1904.11 requires recording on the OSHA 300 log.¹⁷ State regulations often require reporting to an indigenous agency. For example, the California Codes of Regulations specify that cases be reported to the local health officer.^18,19

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SYSTOC^© Resources

Occupational Health Research’s web site at www.systoc.com provides an excellent algorithm
for busy practitioners that covers employee tuberculosis testing.²⁰ Note that retesting is recommended to determine a possible booster effect (described earlier) to identify employees that may have had TB disease in the remote past but whose preliminary skin test result is negative. SYSTOC software includes a tuberculosis module that stores data from a TB monitoring program and includes a recall function for follow up appointments and periodic monitoring.

Summary

TB surveillance is an important responsibility of the occupational medicine clinic. Federal, state, and other legislative mandates require that knowledgeable attention be given to employees at risk of exposure to tuberculosis. Further, the clinic can serve as a valuable resource to the employer that may not be familiar with TB surveillance regulations, assuring effective health monitoring as well as enhancing client-provider relationships.

TB skin testing must be administered and interpreted carefully and accurately. Certification of testing staff may be required. A positive test reaction requires medical management. If a negative result is observed and the patient’s prior test was more than a year prior, two-step testing should be considered. Diagnosis of TB disease requires employer reporting on the OSHA 300 log and may require reporting by the provider to the local health officer. .

Footnotes

1 http://www.wits.ac.za/myco/html/h_tb.htm.

2 http://www.state.nj.us/health/cd/tbhistry.htm.

6 http://www.cdc.gov/nchstp/tb/pubs/mmwr/rr4411.pdf.

7 http://www.cdc.gov/niosh/pdfs/99-143.pdf.

8 http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5210a1.htm.

9 http://www.lapublichealth.org/acd/procs/b73/Part%202.pdf.

12 http://www.cdc.gov/nchstp/tb/pubs/corecurr/default.htm.

13 http://www.cdc.gov/mmwr/preview/mmwrhtml/00038873.htm.

14 http://www.cdc.gov/nchstp/tb/pubs/corecurr/default.htm.

15 http://www.acoem.org/guidelines/article.asp?ID=27.

16 http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5211a1.htm.

18 http://ccr.oal.ca.gov/cgi-bin/om_isapi.dll?clientID=83081&advquery=72537&infobase=ccr&record={60B9B}&softpage=Browse_Frame_Pg42&x=29
&y=16&zz=.

19 http://lapublichealth.org/tb/tbcmr.htm.

20 http://www.systoc.com/outcomes_protocols/Tuberculosis%20Employee%20Testing.htm.