25.  Screening for Tuberculous Infection-Including Bacille Calmette-

Gurin Immunization

RECOMMENDATION

Screening for tuberculous infection with tuberculin skin testing is

recommended for asymptomatic high-risk persons. Bacille Calmette-

Gurin (BCG) vaccination should be considered only for selected high-risk

individuals (see Clinical Intervention).

Burden of Suffering

About 10-15 million persons in the United States are infected with

Mycobacterium tuberculosis.1 More than 24,000 reported cases of

tuberculosis (TB) occurred in the U.S. in 1994.1a,2 This disease is

associated with considerable morbidity from pulmonary and

extrapulmonary pathology. Pulmonary symptoms are progressive and

include cough, hemoptysis, dyspnea, and pleuritis. Extrapulmonary TB can

involve the bones, joints, pericardium, and lymphatics, and it can cause

spinal cord compression from Pott's disease. Death is more common in

older patients and infants, with estimated case-fatality rates ranging

from 0.3% in adolescents to 18.5% in the elderly.3 Newborns and infants

also experience significant morbidity from this disease.

The incidence of TB is greatest in Asians, Pacific Islanders, blacks,

American Indians, Alaska Natives, and Hispanics. About one third of all

reported cases in the U.S. occur in blacks, 20% occur in Hispanics, 14%

occur in Asians and Pacific Islanders, and 1% occur in American Indians

and Alaska Natives.2 About 30% of new cases occur in foreign-born

immigrants.2 The prevalence in homeless persons is 1-7% for clinically

active TB and 18-51% for asymptomatic M. tuberculosis infection.4

After experiencing a steady decline from 1963 to 1984, reported TB cases

increased by 20% from 1985 to 1992.2 A disproportionately large number

of new cases are occurring among black and Hispanic persons, among

whom there was a 41% increase in reported TB cases between 1985 and

1992.2 Infection with human immunodeficiency virus (HIV) is a major

contributor to the recent increase in TB cases. Persons infected with HIV

are more than 100 times more likely to develop active TB than are persons

with competent immune systems, and the onset of the disease is often

more rapid.5 Reports of multidrug-resistant TB have also increased in

recent years. Nationally, the proportion of new cases resistant to both

isoniazid (INH) and rifampin increased from 0.5% in 1982 to 3.3% in the

first quarter of 1991.6 In New York City, as many as 33% of cases are

resistant to INH or rifampin.7 Reported case-fatality rates in patients

with multidrug-resistant TB, most of whom are infected with HIV, have

been as high as 72-89% (the rate is about 30-40% for immunocompetent

individuals).5 The latest data indicate a 9% decrease in annually reported

TB cases from 1992 to 1994, in part reflecting intensified federal, state,

and local TB control efforts.1a

Accuracy of Screening Tests

Tuberculin skin testing is the principal means of detecting M. tuberculosis

infection in asymptomatic persons. Although some authors recommend

chest radiography as a first-line test in high-risk populations,8

roentgenography is generally considered to be inappropriate as the initial

screening test for detecting tuberculous infection in asymptomatic

persons. It is important, however, as a follow-up test to identify active

pulmonary TB in infected persons identified through tuberculin testing.

The most accurate tuberculin skin test is the Mantoux test, in which 5

units (5 TU) of tuberculin purified protein derivative (PPD) are injected

intradermally to detect delayed hypersensitivity reactions within 48-72

hours.

The frequency of false-positive and false-negative tuberculin skin tests

depends on a number of variables, including immunologic status, the size

of the hypersensitivity reaction, and the prevalence of atypical

mycobacteria. In certain geographic areas, cross-reacting atypical

mycobacteria (as well as previous BCG vaccination) can produce

intermediate size reactions, thereby limiting the specificity of the

test.9-11 False-positive results can also be produced by improper

technique (e.g., measuring erythema rather than induration),

hypersensitivity to PPD constituents, an Arthus reaction, and cellulitis.

Prior BCG vaccination may produce false-positive indurations, but these

are generally less than 10 mm in diameter. Moreover, because many BCG

vaccinees either lose their immunity over time or do not convert, large

indurations cannot be confidently attributed to prior BCG

vaccination.12,13 False-negative reactions, which are estimated to occur

in about 5-10% of patients, can be observed early in infection before

hypersensitivity develops, in anergic individuals and those with severe

illnesses (including active TB), in newborns and infants less than 3

months of age, and as a result of improper technique in handling the PPD

solution, administering the intradermal injection, and interpreting the

results.11 Other limitations of the Mantoux test include the time and skill

required for proper administration and variability among clinicians in

interpreting results.14

Multiple puncture tests (e.g., tine, Mono-Vacc) are less expensive and

easier to administer than the Mantoux test. Studies evaluating the

accuracy of these devices, however, have produced inconsistent results. In

general, the evidence suggests that multiple puncture tests have poor

specificity and may have inadequate sensitivity when compared with the

Mantoux test.15-17 Some of this inaccuracy is due to inconsistencies in

the dose of injected tuberculin delivered by multiple puncture tests.

Patient compliance can also affect the effectiveness of tuberculin skin

testing because patients must return to the clinician 48-72 hours after

the injection to have the test interpreted. Studies in pediatric patients

report noncompliance rates of 28-82%.18-20

Persons who are tuberculin test negative may need repeat testing, but

there are inadequate data from which to determine the optimal frequency

of PPD screening. In the absence of such data, clinical decisions regarding

the need for repeat testing and its frequency should be based on the

likelihood of further exposure to TB and the clinician's level of confidence

in the accuracy of the test results. Some negative reactions to tuberculin

skin tests require immediate retesting (two-step testing) to help

determine whether future positive reactions are due to the booster

phenomenon or to new conversion. A positive result on the second test,

typically performed 1-3 weeks later, suggests that the patient has been

previously infected (boosted reaction), whereas a negative result on the

second test followed by a positive result on subsequent testing suggests

recent conversion. Two-step testing has become more common in

screening health care workers21 and other population groups (e.g., elderly

nursing home residents) for tuberculous infection.

Effectiveness of Early Detection

The early detection of tuberculin reactivity is of potential benefit

because chemoprophylaxis with INH is an effective means of preventing

the subsequent development of active TB.22 A review of 14 controlled

trials found that efficacy in preventing clinical disease ranges between

25% and 88% among persons assigned to a 1-year course of INH.22 Among

individuals who complete the course of chemoprophylaxis, efficacy is

greater than 90%.23,24 Some studies suggest that 6 months of INH therapy

in adults are nearly as effective as 12 months of treatment.23,26

Preventive INH therapy is also of potential public health value in

preventing future disease activity and transmission of the organism to

household members and other close contacts. 

A number of factors, however, limit the effectiveness of INH

chemoprophylaxis. Some organisms are resistant to INH and other agents.5

Patient compliance with a 6-12-month regimen is often difficult. The

most important limitation of INH is its potential hepatotoxicity. INH-

induced hepatitis occurs in about 0.3-2.3% of patients,27 the frequency

increasing with age and other factors (e.g., alcohol use). The condition can

be fatal, but the exact frequency of fatal INH-induced hepatitis is

uncertain. Mortality rates for persons with INH-related hepatitis were

reported to be as high as 4-7% in one major study, with risk increasing

directly with age (zero for persons less than 20 years of age, 0.3% for

persons 20-34 years of age, 1.2% for persons 35-49 years of age, 2.3% for

persons 50-64 years of age).28 These data may overestimate the actual

mortality from INH-induced hepatitis because the local incidence of

cirrhosis-related deaths was increased in one of the communities

participating in the study.29 More recent analyses of published and

unpublished data have estimated that the incidence of fatal INH-induced

hepatitis is about 1-14/100,000 persons started on preventive

therapy.30,31 The risk may be lowered by performing periodic liver

function tests while patients take INH. In persons who develop

complications from INH, the resulting interruption of INH therapy before

completion of the 1-year course may also lower the effectiveness of TB

prevention.24

Although the benefits of INH probably outweigh its side effects in persons

at high risk for developing active TB (see Clinical Intervention for

description of high-risk groups), it is uncertain from available data

whether low-risk, asymptomatic persons with a reactive tuberculin skin

test are at sufficient risk of developing TB to justify the risks of INH-

induced hepatitis. Epidemiologic calculations suggest that the annual

incidence of TB in a low-risk population is less than 0.1%,32,33 and that

the lifetime probability of developing active TB ranges from 1.2% at age

20 to 0.37% at age 80.34 Depending on the risk of INH-induced hepatitis, it

is possible for complications from INH treatment to be more likely than

the development of TB. In the absence of definitive clinical studies to

clarify this issue, investigators have used decision analysis techniques to

compare the benefits and risks of INH in tuberculin skin reactors of

different ages. The results of these analyses have been inconsistent. One

group concluded that benefits outweigh risks until the patient exceeds age

45;35 another found that treatment was beneficial at all ages;27 and

another analysis concluded that INH should be withheld at all ages in the

absence of other risk factors.34 A decision analysis in young adults

concluded that treatment was not beneficial in this age group.32 An

analysis for elderly tuberculin skin reactors concluded that INH would

neither improve nor worsen 5-year survival but would decrease the risk of

developing active disease.33 An analysis for HIV-infected injection drug

users concluded that, with the exception of black women, such patients

would benefit from INH therapy even in the absence of tuberculin skin

testing.36

Bacille Calmette-Gurin (BCG) Vaccination

Primary prevention through vaccination represents an alternative

approach to the prevention of TB. BCG, a live vaccine derived from

attenuated Mycobacterium bovis, has been used worldwide for more than

50 years to prevent TB. Clinical trials of the efficacy of BCG have yielded

inconsistent results since the early 1930s, however, with reported levels

of protection ranging from -56% to 80%.37,38 Observational studies have

shown that the incidence of the disease is lower in vaccinated children

than in unvaccinated controls.39-43 Factors contributing to the wide

variation in results in BCG vaccine efficacy include genetic changes in the

bacterial strains as well as differences in production techniques, methods

of administration, and the populations and environments in which the

vaccine has been studied.44 A meta-analysis of 14 trials and 12 case-

control studies concluded that BCG offered 50% protection against TB

overall and 64-71% protection against TB meningitis and TB-related

death.45

The potential adverse effects of BCG vaccination include prolonged

ulceration and local adenitis, which occur in about 1-10% of vaccinees.

The risk varies with the type of vaccine used, the population, and the

methods used to measure complications. Osteomyelitis and death from

disseminated BCG infection are estimated to occur in one case per million

doses administered.44

In the U.S., where the risk of becoming infected with M. tuberculosis is

relatively low, the disease can currently be controlled most successfully

by screening and early treatment of infected persons. However, BCG

vaccination may have a role in the U.S. for persons with special exposures

to individuals with active TB, such as uninfected children who are at high

risk for continuous or repeated exposure to infectious persons who are

undetected or untreated,44 or a future role in light of escalating

multidrug resistance.

Recommendations of Other Groups

The Centers for Disease Control and Prevention (CDC), American Thoracic

Society (ATS), and other members of the Advisory Committee for

Elimination of Tuberculosis recommend screening the following groups for

tuberculous infection: persons infected with HIV; close contacts of

persons with TB; persons with medical risk factors associated with TB;

immigrants from countries with high TB prevalence; medically

underserved low-income populations; injection drug users; and residents

and employees of high risk facilities.46 Similar recommendations have

been issued by the American Academy of Family Physicians.55 Although

the Canadian Task Force on the Periodic Health Examination recommends

screening high-risk groups, it gave an "E" recommendation (good evidence

against performing the maneuver in the periodic health examination) to

screening low-risk persons.46a The American Academy of Pediatrics

(AAP) recommends against routine annual skin testing of children who

lack risk factors and live in low-prevalence communities. The AAP does

recommend annual Mantoux testing of high-risk children, as well as

consideration of less frequent periodic testing (e.g., at ages 1, 4-6, and

11-16 years) of low-risk children who live in high-prevalence

communities or have unreliable histories.47 The Bright Futures guidelines

recommend annual testing for persons of low socioeconomic status, those

in high prevalence areas, those exposed to TB, and immigrants.48 The

American Medical Association's Guidelines for Adolescent Preventive

Services (GAPS) recommend annual testing for adolescents in high-risk

settings including those in homeless shelters, correctional institutions,

and health care facilities.49

Recommendations on how to perform tuberculin skin testing have been

issued by the CDC and ATS.11 The CDC has recently issued guidelines on

preventing transmission in health care facilities, which include specific

recommendations on the categories of health care workers to include in

skin-testing programs and the frequency with which they should be

tested.50 Guidelines for the treatment of converters have been issued in a

joint statement by the ATS, AAP, CDC, and Infectious Disease Society of

America.51,52 The CDC has also issued recommendations on multidrug

preventive therapy for converters with suspected contact with drug-

resistant TB.5 Screening certain populations for tuberculous infection is

required by law in 44 states.7

Recommendations on BCG vaccination have been issued in a joint

statement by the Immunization Practices Advisory Committee and the

Advisory Committee for Elimination of Tuberculosis.44 They recommended

limiting BCG vaccination in the U.S. to tuberculin-negative infants and

children who cannot be placed on INH and who have continuous exposure to

persons with active disease, those with continuous exposure to patients

with organisms resistant to INH or rifampin, and those belonging to groups

with a rate of new infections greater than 1% per year and for whom the

usual surveillance and treatment programs may not be operationally

feasible.

CLINICAL INTERVENTION

Screening for tuberculous infection by tuberculin skin testing is

recommended for all persons at increased risk of developing tuberculosis

(TB) ("A" recommendation). Asymptomatic persons at increased risk

include persons infected with HIV, close contacts of persons with known

or suspected TB (including health care workers), persons with medical

risk factors associated with TB, immigrants from countries with high TB

prevalence (e.g., most countries in Africa, Asia, and Latin America),

medically underserved low-income populations (including high-risk racial

or ethnic minority populations), alcoholics, injection drug users, and

residents of long-term care facilities (e.g., correctional institutions,

mental institutions, nursing homes). The Mantoux test involves the

intradermal injection of 5 units of tuberculin PPD and the subsequent

examination of the injection site 48-72 hours later. Current minimum

criteria for a positive skin test, based on observational data and expert

opinion, are 15-mm diameter for low-risk individuals, 10-mm diameter

for high-risk individuals (e.g., immigrants, medically underserved low-

income populations, injection drug users, residents of long-term care

facilities, persons with conditions that increase TB risk, infants, and

children less than 4 years of age), and 5-mm diameter for persons at very

high risk (e.g., persons infected with HIV,  persons with abnormal chest

radiographs, recent contacts of infected persons). Prior BCG vaccination is

not currently considered a valid basis for dismissing positive results.

Persons with negative reactions who are at increased risk of anergy (e.g.,

HIV-infected individuals) can be skin-tested for anergy,53 but this

procedure is now considered optional in current CDC guidelines.46

Treatment decisions in HIV-infected anergic patients should be made on

an individual basis.54 The frequency of tuberculin skin testing is a matter

of clinical discretion.

Persons with a positive PPD test should receive a chest x-ray and clinical

evaluation for TB. Those lacking evidence of active infection should

receive INH prophylaxis if they meet criteria defined in recent

guidelines.52 Briefly, these criteria recommend INH prophylaxis in

persons under 35 years of age who are from high-prevalence countries;

medically underserved, low-income, high-prevalence populations; or long-

term care facilities. It is also recommended in persons of any age with

HIV infection or increased risk of HIV infection, other medical conditions

that increase the risk of TB, or close contact with patients with newly

diagnosed TB or skin test conversion. Screening for HIV infection may be

indicated in recent converters (see Chapter 28). Patients with possible

exposure to drug-resistant TB should be treated according to current

recommendations for multidrug preventive therapy.5 Directly observed

therapy-observation of the patient by a health care worker as the

medication is taken-may be indicated in patients who are unlikely to be

compliant.

BCG vaccination against TB should be considered only for tuberculin-

negative infants and children who cannot be placed on INH and who have

continuous exposure to persons with active disease, those with continuous

exposure to patients with organisms resistant to INH or rifampin, and

those belonging to groups with a rate of new infections greater than 1%

per year and for whom the usual surveillance and treatment programs may

not be operationally feasible ("B" recommendation). These groups may also

include persons with limited access to or willingness to use health care

services.

The draft update of this chapter was prepared for the U.S. Preventive

Services Task Force by Steven H. Woolf, MD, MPH.

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