TB Facts for Health Care Workers
Identification of Persons with TB Infection and Disease
Identifying TB Infection
A person exposed to an individual with infectious TB or who has
other risk factors for TB as noted above should be given a tuberculin
The Mantoux tuberculin skin test is the preferred method of skin
testing. The Mantoux tuberculin skin test is the intradermal injection
of purified protein derivative (PPD) of killed tubercle bacilli,
usually on the inner forearm. The site is examined by a trained
health care worker 48 to 72 hours after injection for induration
(palpable swelling). The diameter of induration is measured and
recorded; erythema or bruising is disregarded.
The criteria endorsed by the American Thoracic Society and CDC
for a positive tuberculin skin-test result (Table 1) are intended
to increase the likelihood that persons at high risk for TB will
be candidates for preventive therapy and that persons having tuberculin
reactions not caused by M. tuberculosis will not receive
unnecessary diagnostic evaluation or treatment.
Summary of interpretation of tuberculin skin-test results
- An induration of ³5 mm is classified as positive
in the following:
Persons who have had recent close contact with persons who
have active TB;
Persons who have human immunodeficiency virus (HIV) infection
or risk factors for HIV infection but unknown HIV status
(e.g., injecting drug users);
Persons who have fibrotic chest radiographs consistent
with healed TB.
- An induration of ³10 mm is classified as positive
in all persons who do not meet any of the above criteria,
but who belong to one or more of the following groups having
high risk for TB:
Injecting-drug users known to be HIV seronegative;
Persons who have other medical conditions that have been
reported to increase the risk for progressing from latent
TB infection to active TB. These medical conditions include
diabetes mellitus, conditions requiring prolonged high-dose
corticosteroid therapy and other immunosuppressive therapy
(including bone marrow and organ transplantation), chronic
renal failure, some hematologic disorders (e.g., leukemias
and lymphomas), other specific malignancies (e.g., carcinoma
of the head or neck), weight loss of ÿ10% below ideal
body weight, silicosis, gastrectomy, jejunoileal bypass;
Residents and employees of high-risk congregate settings:
prisons and jails, nursing homes and other long-term facilities
for the elderly, health-care facilities (including some
residential mental health facilities), and homeless shelters;
Foreign-born persons recently arrived (i.e., within the
last 5 years) from countries having a high prevalence
or incidence of TB;
Some medically underserved, low-income populations, including
migrant farm workers and homeless persons;
High-risk racial or ethnic minority populations, as defined
Children <4 years of age or infants, children, and
adolescents exposed to adults in high-risk categories.
- An induration of ³15 mm is classified as positive
in persons who do not meet any of the above criteria.
For each of the risk groups listed in Table 1, reactions below
the cutoff point are considered negative. A negative TB skin test
result does not absolutely rule out TB infection, especially in
persons with TB-like symptoms, HIV infection, or AIDS. Also, because
it takes 2 to 10 weeks from the time of exposure for a person to
react to tuberculin, the initial skin test result of an infected
contact may be falsely negative. Therefore, a repeat skin test 10
weeks post exposure is warranted.
Some persons with both HIV and TB infections may have false negative
skin test reactions (anergy). Anergy refers to the inability
to react to a skin test antigen even though the person is infected
with the organism being tested. Several delayed-type hypersensitivity
(DTH) antigens (such as tetanus toxoid, mumps or Candida)
administered by the Mantoux technique have been used in an attempt
to determine anergy status. Recent CDC recommendations, however,
note several factors that limit the usefulness of anergy skin testing.
These include problems with standardization and reproducibility,
the low risk for TB associated with a diagnosis of anergy, and the
lack of apparent benefit of preventive therapy for groups of anergic
HIV-infected persons. Therefore, the use of anergy testing in conjunction
with PPD testing is no longer routinely recommended for screening
programs for M. tuberculosis infection conducted among persons
infected with HIV in the United States.
Persons with latent TB infection should be evaluated for HIV risk
behaviors and offered counseling and HIV-antibody testing if such
behaviors are present.
Many foreign countries still use BCG as part of their TB
control programs, especially for infants. In persons vaccinated
with BCG, sensitivity to tuberculin is highly variable, depending
upon the strain of BCG used and the group vaccinated. There is no
reliable method of distinguishing tuberculin reactions caused by
BCG from those caused by natural infections. A reaction to tuberculin
in a person with a history of BCG vaccination is more likely to
be due to infection with M. tuberculosis if:
In a BCG-vaccinated person who has any of the preceding risk factors,
a positive tuberculin reaction probably indicates infection with M.
tuberculosis. Such persons should be evaluated for isoniazid preventive
therapy after disease has been ruled out.
- the induration is large
- the person was vaccinated a long time ago
- the person is a recent contact of a person with infectious TB
- there is a family history of TB
- the person comes from an area where TB is common
- chest radiograph findings show evidence of previous TB
Identifying TB Disease
If the skin test result is positive or if symptoms suggestive of
TB are present (e.g., productive and prolonged cough, fever, chills,
loss of appetite, weight loss, fatigue, or night sweats), a chest
radiograph should be obtained to help rule out active pulmonary
TB. The chest radiograph may also be used to detect the presence
of fibrotic lesions suggestive of old, healed TB or silicosis.
Acid-fast bacilli (AFB) smears and cultures should be performed
on sputum specimens of all persons who have symptoms of TB or whose
chest radiograph suggests TB. A positive AFB smear is an indication
for beginning treatment for TB. However, a positive AFB smear may
also indicate the presence of nontuberculous mycobacteria. A positive
culture for Mycobacterium tuberculosis is the only definitive
proof of TB disease.
Health care providers of HIV-infected persons should be aware of
atypical patterns of TB disease in these persons. Extrapulmonary
TB is more common. Also, pulmonary TB may present in an unusual
manner (e.g., in the lymph nodes or in the lower part of the lungs).
All persons with TB infection or TB disease should be offered counseling
and HIV-antibody testing, because medical management may be altered
in the presence of HIV infection.
Maintain a high index of suspicion for TB in persons with undiagnosed
pulmonary disease, especially in persons who are HIV seropositive.
Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination - http://www.cdc.gov/tb
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