Two-step tuberculin testing in staff and residents of a nursing home

Determinants of tuberculin reactivity among health care workers: Interpretation of positivity following BCG vaccination

OBJECTIVE

To determine the extent to which a history of Bacille Calmette-Guerin (BCG) vaccination influences the likelihood of positive tuberculin skin test (TST) results.

DESIGN

Cross-sectional survey using a hospital-based tuberculosis surveillance program.

SETTING

Health Sciences Centre, a tertiary care hospital in Winnipeg, Manitoba.

METHODS

The 476 health care workers (HCWs) who had TST as part of the surveillance program between 1993 and 1997 constituted the study population. The two-step test was done in 91% of the participants who did not have a positive initial test, defined as 10 mm or greater of induration. Data were gathered through chart review supplemented by a short questionnaire administered to the HCWs.

MAIN RESULTS

One hundred and thirty-eight HCWs (29%) had a positive TST. In a stepwise, multiple logistic model controlling for age, sex, job title, work area, age of receiving BCG, time since BCG and duration of employment, only a history of BCG vaccination (odds ratio [OR] 22; 95% CI 12 to 41) and birth outside of Canada (OR 2.6; 95% CI 1.4 to 5.8) were significantly associated with a positive TST. When the definition of a positive TST was modified by increments of 1 mm, from 10 mm up to 20 mm of induration in BCG recipients, BCG was associated with positive reactions with indurations up to 19 mm but not 20 mm or greater. The OR declined with each increment. Of the 84 HCWs who were documented to have at least 20 years between BCG vaccination and testing, 41 (49%) had positive reactions.

CONCLUSIONS

BCG vaccination can produce lasting tuberculin reactivity, and indurations of 19 mm or less may be due to the effects of the vaccine.

Two-Step Tuberculin Skin Testing in Drug Users

To assess the utility of booster testing and to identify factors associated with a positive booster test, two-step tuberculin testing was performed in drug users recruited from methadone treatment. Participants also received a standardized interview on demographics and testing for HIV and CD4+ lymphocyte count. Of 619 enrollees completing the protocol, 174 (28%) had a positive PPD and 24 of the remaining 445 (5%) had a positive booster test. On multivariate analysis, boosting was associated with older age (adjusted odds ratio [ORadj] 2.38/decade, 95% confidence interval [CI] 1.34-4.22), history of using crack cocaine (ORadj 2.61, 95% CI 1.10-6.18) and a history of working as a home health aide (ORadj 4.23, 95% CI 1.39-12.86). Two-step tuberculin skin testing increased the proportion of participants with latent tuberculosis infection from 22% to 25%. Given the effectiveness of chemoprophylaxis, booster testing should be considered when drug users are screened for tuberculosis infection.

Influence of Bacille Calmette-Guerin Vaccination on Size of Tuberculin Skin Test Reaction: To What Size?

BACKGROUND

Previous bacillus Calmette-Guerin (BCG) vaccination can confound the results of a tuberculin skin test (TST). We sought to determine a cutoff diameter of TST induration beyond which the influence of BCG vaccination was negligible in evaluating potential Mycobacterium tuberculosis infection in a population of health care workers with a high vaccination rate and low incidence of tuberculosis.

METHODS

From 1991 through 1998, all new employees at the University Hospital of Lausanne, Switzerland, underwent a 2-step TST at entry visit. We also gathered information on demographic characteristics, along with factors commonly associated with tuberculin positivity, including previous BCG vaccination, history of latent M. tuberculosis infection, and predictors for M. tuberculosis infection.

RESULTS

Among the 5117 investigated subjects, we found that influence of BCG vaccination on TST results varied across categories of age (likelihood ratio test, 0.0001). Prior BCG vaccination had a strong influence on skin test results of <or=18 mm in diameter among persons <40 years old, compared with the influence of factors predictive of M. tuberculosis infection. Prior latent M. tuberculosis infection and travel or employment in a country in which tuberculosis is endemic also had significant influences.

CONCLUSIONS

Interpretation of TST reactions of <or=18 mm among BCG-vaccinated persons <40 years of age must be done with caution in areas with a low incidence of tuberculosis. In such a population, except for persons who have never been vaccinated, TST reactions of <or=18 mm are more likely to be the result of prior vaccination than infection and should not systematically lead to preventive treatment.

Tuberculosis infection notification in Swiss medical students during their clinical electives

OBJECTIVE

The aim of this study was to assess the tuberculin skin test conversion incidence in Swiss medical students.

METHODS

This was a prospective cohort study of medical students at the University of Zurich, using a standardized tuberculin skin test before and after clinical electives.

RESULTS

Two hundred and sixty-two students accepted the invitation to the pre-clerkship test, and 155 (59.2%) subjects were retested after an average period of 2.25 years. An increase of more than 10 mm in the transverse diameter of the induration in the retest compared to the baseline test was observed in 12 (7.7%) students. The annual conversion rate was 3.4% (95% CI 1.8-6.0%).

CONCLUSIONS

Even in an industrialized country, the risk of tuberculosis infection--as estimated by the tuberculin skin test--is substantial for health care professionals. Possible explanations for the high incidence and possible bias are discussed.

A meta-analysis of the effect of Bacille Calmette Guérin vaccination on tuberculin skin test measurements

BACKGROUND

The accurate diagnosis of latent tuberculosis infection (LTBI) is an important component of any tuberculosis control programme and depends largely on tuberculin skin testing. The appropriate interpretation of skin test results requires knowledge of the possible confounding factors such as previous BCG vaccination. Uncertainty about the effect of BCG vaccination on tuberculin skin testing and the strength with which recommendations are made to individual patients regarding treatment of LTBI have identified a need to analyse the available data on the effect of BCG on skin testing. A meta-analysis of the evidence for the effect of BCG vaccination on tuberculin skin testing in subjects without active tuberculosis was therefore performed.

METHODS

Medline was searched for English language articles published from 1966 to 1999 using the key words "BCG vaccine", "tuberculin test/PPD", and "skin testing". Bibliographies of relevant articles were reviewed for additional studies that may have been missed in the Medline search. Articles were considered for inclusion in the meta-analysis if they had recorded tuberculin skin test results in subjects who had received BCG vaccination more than 5 years previously and had a concurrent control group. Only prospective studies were considered. The geographical location, number of participants, type of BCG vaccine used, type of tuberculin skin test performed, and the results of the tuberculin skin test were extracted.

RESULTS

The abstracts and titles of 980 articles were identified, 370 full text articles were reviewed, and 26 articles were included in the final analysis. Patients who had received BCG vaccination were more likely to have a positive skin test (5 TU PPD: relative risk (RR) 2.12 (95% confidence interval (CI)1.50 to 3.00); 2 TU RT23: 2.65 [corrected] (95% CI 1.83 to 3.85). The effect of BCG vaccination on PPD skin test results was less after 15 years. Positive skin tests with indurations of >15 mm are more likely to be the result of tuberculous infection than of BCG vaccination.

CONCLUSIONS

In subjects without active tuberculosis, immunisation with BCG significantly increases the likelihood of a positive tuberculin skin test. The interpretation of the skin test therefore needs to be made in the individual clinical context and with evaluation of other risk factors for infection. The size of the induration should also be considered when making recommendations for treatment of latent infection.

Tuberculosis tracking: determining the frequency of the booster effect in patients and staff

BACKGROUND

Two-step tuberculin skin testing, which is recommended to exclude the booster effect as a cause of converting nonreactive skin test responses to reactive responses, can be expensive and logistically challenging. We studied the booster effect in our patients and staff to determine its frequency and to identify factors that might predict its occurrence.

METHODS

Hospital staff members and long-term care patients were given 2-step Mantoux tests and evaluated prospectively.

RESULTS

Of 619 staff members tested, the initial tuberculin response was reactive in 39 (6.3%). Of the 97 nonreactive staff members who presented for retesting 6 to 30 days later, 6 were now reactive (6.2%; [95% CI, 2.3%-11.8%]). Twelve (13.6%) of eighty-eight patients were tuberculin reactive on their initial skin test. Of the 37 nonreactive patients appropriately administered their second test, 2 (5.4%, [95% CI, 0.7-18.2%]) were tuberculin-reactive. Thirteen percent of tuberculin-reactive staff members and 16% of tuberculin-reactive patients were identified only after their second skin test. Foreign birth (P =.02) was associated with purified protein derivative response boosting in staff members; anemia was associated with boosting in patients (P =.05).

CONCLUSIONS

Our results support 2-step skin testing of all new employees and patients who are likely to receive periodic retesting. In our population, age alone is an inadequate criterion for selecting candidates for retesting.

Two-step tuberculin testing of passengers and crew on a commercial airplane

OBJECTIVES

We investigated the risk of tuberculosis transmission from a person with highly infectious pulmonary tuberculosis to fellow passengers and crew members on a 14-hour commercial flight. The 2-step tuberculin testing was used to minimize the effects of the booster phenomenon.

METHODS

Passengers and flight crew members identified from airline records were contacted by letter, telephone, or both to notify them of their potential exposure to Mycobacterium tuberculosis. The subjects were advised to undergo Mantoux tuberculin skin testing within the required time period to assess a conversion. In addition, information regarding tuberculosis history and other sources of potential exposure was solicited by means of a questionnaire.

RESULTS

Of the 277 passengers and crew members on the aircraft, 225 (81.2%) responded. Of these, 173 (76.9%) had positive tuberculin results on the first test (induration > 10 mm). Thirteen subjects with negative results refused further testing; 11 (28%) of the remaining 39 exhibited the booster phenomenon on the second test. Subjects who exhibited the booster phenomenon were significantly more likely to have received previous BCG vaccination. Nine contacts with negative results on the initial test had positive results on a third test administered at 12 weeks after the flight exposure Of these, 6 contacts had previous BCG vaccination, old tuberculosis, or a family member with tuberculosis; the remaining 3 reported on other risk factors for positive reactions. None of these 3 contacts had sat in the same section of the plan as the index patient.

CONCLUSIONS

The 2-step tuberculin testing procedure is an effective tool for minimization of the booster effect, thus allowing accurate monitoring of subsequent tuberculin conversion rates. Moreover, the clustering of tuberculin skin test conversions among passengers in this study demonstrates the possible risk of M tuberculosis transmission during air travel.

Evaluation of the two-step tuberculin skin test in health care workers at an inner-city medical center

The increased rate of tuberculosis (TB) infection and transmission from patients to health care workers (HCWs) has brought awareness of the need for better surveillance programs. The two-step purified protein derivative (PPD) skin test decreases the misinterpretation of a "boosted reaction" as a recent infection with Mycobacterium tuberculosis in HCWs. We reviewed the medical records of 4082 HCWs at an inner-city medical center who had PPD skin-testing performed as a component of the TB medical surveillance program during the years 1994 and 1995. Of those HCWs tested, 3896 (95.4%) returned for the PPD skin-test evaluation. Of those 3896 HCWs, 3659 (93.9%) had a negative baseline PPD skin test, and 237 (6.1%) had a positive skin test. Of those HCWs with a negative baseline skin test, 252 (6.9%) were eligible for the second PPD skin test. Of the 241 who returned for their second PPD skin-test reading, six (2.5%) had positive results. All six cases were foreign-born physician residents with a previous history of Bacille bilié de Calmette-Guérin (BCG) vaccination. We conclude that the two-step PPD skin test method is not indicted for HCWs at this urban medical facility.

Benefit of two-step PPD testing of new employees at a New York City hospital

BACKGROUND

Recent concern about nosocomial transmission of tuberculosis has led hospitals to scrutinize employee tuberculin conversion rates. The Centers for Disease Control and Prevention recommends two-step testing of new employees to limit the booster phenomenon. The cost of such a program and its subsequent yield have not recently been examined.

METHODS

Employee health records were retrospectively reviewed of persons hired from 1993 and 1994 at St. Clare's Hospital in New York City, all of whom received two-step testing at time of initial employment.

RESULTS

Of 262 new employees, 107 (41%) had positive tuberculin results on initial testing. The results of 15 (9.7%) of the remaining 155 patients became positive on two-step testing administered 1 week later. Persons with a positive second test result were significantly more likely to be male or foreign born or to have received previous bacille Calmette-Guérin vaccination. Identification of these 15 persons and exclusion of them from probable subsequent conversion prevented an almost 50% increase in the annual conversion rate at our hospital, from 3.2% to 4.7%.

CONCLUSION

Two-step tuberculin testing is an essential means of identifying persons with a baseline positive tuberculin test result, thus allowing accurate reporting of subsequent employee tuberculin conversions.

Tuberculin skin test conversion in hospital employees vaccinated with bacille Calmette-Guérin: recent Mycobacterium tuberculosis infection or booster effect?

OBJECTIVE

A rise in the incidence of purified protein derivative (PPD) skin test conversions among employees at our medical center between 1991 and 1993 prompted an examination of factors associated with PPD skin test conversion. We focused on the effect of bacille Calmette-Guérin (BCG) vaccination on PPD skin test conversion because of changes in employee health service policies in 1990 regarding testing of persons who had received BCG vaccination.

METHODS

The study took place in a university teaching hospital employee health service. Charts of employees who had PPD skin test conversion (> 10 mm increase in induration of the PPD response within 2 years if younger than 35 years of age or > 15 mm if older than 35 years of age) between 1988 and 1993 were reviewed for factors that could have influenced PPD skin test conversion and compared with data from 271 randomly selected charts of employees who underwent annual employee assessments in 1993 but did not have PPD skin test conversion.

RESULTS

PPD skin test conversions rose from 0.06% (1/1604) to 1.3% (22/1760; p = 0.000001) in employees tested between 1988 and 1993. Of 41 persons with PPD skin test conversion between 1991 and 1993, 29 (71%) had received BCG vaccination. Only 21% of control subjects (56/271) had received BCG vaccination (p < 0.000001 for comparison of BCG vaccination among those with PPD skin test conversion with that among control subjects). When BCG recipients were not included as having PPD skin test conversion, there was no significant increase in PPD skin test conversions. Twenty-three BCG recipients had PPD skin test conversion on their second PPD skin tests.

CONCLUSION

A large proportion of PPD skin test conversions at hospitals that employ large numbers of health care workers who have received BCG vaccination may not represent recently acquired tuberculosis. Rather, these conversions may be effects of previous BCG vaccination. Two-step initial PPD skin testing may help to eliminate nearly 80% of such false-positive conversions.

Tuberculosis in the AIDS era

A resurgence of tuberculosis has occurred in recent years in the United States and abroad. Deteriorating public health services, increasing numbers of immigrants from countries of endemicity, and coinfection with the human immunodeficiency virus (HIV) have contributed to the rise in the number of cases diagnosed in the United States. Outbreaks of resistant tuberculosis, which responds poorly to therapy, have occurred in hospitals and other settings, affecting patients and health care workers. This review covers the pathogenesis, epidemiology, clinical presentation, laboratory diagnosis, and treatment of Mycobacterium tuberculosis infection and disease. In addition, public health and hospital infection control strategies are detailed. Newer approaches to epidemiologic investigation, including use of restriction fragment length polymorphism analysis, are discussed. Detailed consideration of the interaction between HIV infection and tuberculosis is given. We also review the latest techniques in laboratory evaluation, including the radiometric culture system, DNA probes, and PCR. Current recommendations for therapy of tuberculosis, including multidrug-resistant tuberculosis, are given. Finally, the special problem of prophylaxis of persons exposed to multidrug-resistant tuberculosis is considered.