Evaluation of a third sequential tuberculin skin test in a chronic care population

Tuberculosis in Long-Term Care Facilities

Persons age 65 and over constitute the largest reservoir of Mycobacterium tuberculosis infection in the United States today. During 1987, 6,150 tuberculosis cases were reported among this high-risk group. These cases represent 27% of the total US tuberculosis morbidity, although this age group constitutes only 12% of the US population. Tuberculosis case rates in the United States are higher among the elderly (20.6 per 100,000) than among all other age groups (average 9.3 per 100,000).

More Americans live in nursing homes than in any other type of residential institution; on any given day approximately 5% of all elderly persons are living in a nursing home. Elderly nursing home residents are at greater risk for tuberculosis than elderly persons living in the community. In a Centers for Disease Control (CDC)-sponsored survey of 15,379 routinely-reported tuberculosis cases from 29 states, 8% of the 4,919 cases that occurred among elderly persons occurred among residents of nursing homes. The incidence of tuberculosis among nursing home residents was 39.2 per 100,000 person years, whereas the incidence of tuberculosis among elderly persons living in the community was 21.5 per 100,000. The observed rate of tuberculosis among nursing home employees was three times the rate expected in employed adults of similar age, race and sex (CDC, unpublished data).

The presence of a booster phenomenon among contacts of active pulmonary tuberculosis cases: a retrospective cohort

Background

Assuming a higher risk of latent tuberculosis (TB) infection in the population of Rio de Janeiro, Brazil, in October of 1998 the TB Control Program of Clementino Fraga Filho Hospital (CFFH) routinely started to recommend a two-step tuberculin skin test (TST) in contacts of pulmonary TB cases in order to distinguish a boosting reaction due to a recall of delayed hypersensitivity previously established by infection with Mycobacterium tuberculosis (M.tb) or BCG vaccination from a tuberculin conversion. The aim of this study was to assess the prevalence of boosted tuberculin skin tests among contacts of individuals with active pulmonary tuberculosis (TB).

Methods

Retrospective cohort of TB contacts ≥ 12 years old who were evaluated between October 1^st, 1998 and October 31^st 2001. Contacts with an initial TST ≤ 4 mm were considered negative and had a second TST applied after 7–14 days. Boosting reaction was defined as a second TST ≥ 10 mm with an increase in induration ≥ 6 mm related to the first TST. All contacts with either a positive initial or repeat TST had a chest x-ray to rule out active TB disease, and initially positive contacts were offered isoniazid preventive therapy. Contacts that boosted did not receive treatment for latent TB infection and were followed for 24 months to monitor the development of TB. Statistical analysis of dichotomous variables was performed using Chi-square test. Differences were considered significant at a p < 0.05.

Results

Fifty four percent (572/1060) of contacts had an initial negative TST and 79% of them (455/572) had a second TST. Boosting was identified in 6% (28/455). The mean age of contacts with a boosting reaction was 42.3 ± 21.1 and with no boosting was 28.7 ± 21.7 (p = 0.01). Fifty percent (14/28) of individuals whose test boosted met criteria for TST conversion on the second TST (increase in induration ≥ 10 mm). None of the 28 contacts whose reaction boosted developed TB disease within two years following the TST.

Conclusion

The low number of contacts with boosting and the difficulty in distinguishing boosting from TST conversion in the second TST suggests that the strategy of two-step TST testing among contacts of active TB cases may not be useful. However, this conclusion must be taken with caution because of the small number of subjects followed.

Predictors of Positive Tuberculin Skin Test (TST) Results after 2‐Step TST among Health Care Workers in Manitoba, Canada

BACKGROUND

Baseline 2-step tuberculin skin testing (TST) is recommended for health care workers (HCWs) to identify cases of the "boosting phenomenon" (i.e., a negative initial TST result followed by a positive result) and to track the risk of acquiring occupational tuberculosis. However, the 2-step TST has been shown to be insufficient to identify all cases of the booster phenomenon in older adults and refugees. The objective of this study was to identify whether a history of bacille Calmette-Guérin (BCG) vaccination and foreign birth--variables that are known to be associated with the booster phenomenon--remain predictors of a positive TST result in a group of HCWs documented to have negative 2-step TST results (i.e., 2 TSTs done 7-28 days apart with indurations <10 mm in diameter).

METHODS

We performed a retrospective analysis of an employee database in a tertiary care hospital in Winnipeg, Canada. The study population was comprised of 698 HCWs with negative 2-step TST results who underwent a TST 0-2 years after completion of the 2-step procedure.

RESULTS

Forty-six HCWs (6.6%) had a positive TST result 0-2 years after the 2-step test. In a multiple logistic regression analysis controlling for age, BCG vaccination, foreign birth, sex, and work setting, only history of BCG vaccination (odds ratio [OR], 8.38; 95% confidence interval [CI], 4.04-17.4), foreign birth (OR, 3.19; 95% CI, 1.53-6.62), and high-risk work setting (OR, 2.93; 95% CI, 1.44-5.95) were associated with a positive TST result.

CONCLUSIONS

Even for HCWs with negative results of 2-step TST, foreign birth and history of BCG vaccination are associated with a positive result of a future TST. Some positive TST results in such HCWs are related to nonoccupational factors, including delayed boosting, rather than to conversion due to recent tuberculosis contact.

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.

What does tuberculin reactivity after bacille Calmette-Guérin vaccination tell us?

The effect of bacille Calmette-Guérin (BCG) vaccination on tuberculin reactivity is briefly reviewed. BCG vaccination will almost invariably result in tuberculin conversion with a positive tuberculin skin test developing 4-8 weeks after vaccination. However, these tuberculin reactions will wane-rapidly in all individuals who receive the vaccine in the neonatal period and more slowly in those who are vaccinated at an older age such as during the primary-school years. Of BCG vaccine recipients whose initial tuberculin skin test is negative, 10%-25% will have a positive tuberculin skin test if they are retested within 1-4 weeks-the so-called "booster phenomenon. " There is no relationship between tuberculin reactivity after BCG vaccination and the protective efficacy of the vaccine against development of active tuberculosis. Therefore, the ideal BCG vaccine would produce a scar at the site of injection to identify individuals who have been vaccinated but would have no effect on tuberculin reactivity.

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.

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

This study examined the prevalence and determinants of tuberculin reactors and the booster response in 272 (97%) residents and 218 (69%) staff of an urban nursing home where a case of miliary TB was being investigated. Many subjects were foreign born (56%), and 15% had a history of BCG vaccination (34% of staff). Testing was done with 5 TU PPD-S (Connaught). Those with < 10 mm induration at 48 h were retested at 1 wk. Test sizes > 9 mm were classified positive (reactors). A questionnaire was given to collect information on risk factors for a positive test. Results showed that 28% (36% staff and 22% of residents) of subjects were reactors at the initial test, 6% at the booster test (staff and residents), and 32% at either test (40% staff and 26% residents). BCG (OR 4.8) and foreign birth (OR 1.7) were significantly associated with total reactors. The association with foreign birth was inversely related to the time since immigration. Only BCG was associated with a positive booster test (OR 6.7). Of positive tuberculin reactions in individuals with a history of BCG, 72% were attributed to the vaccine. We concluded that (1) staff as well as residents should be two-step tested when retesting is anticipated; (2) the prevalence of tuberculin reactors is highly related to the prevalence of BCG vaccinees and foreign birth; and (3) chemoprophylaxis is probably not indicated for isolated tuberculin reactors with a history of BCG.

Repeated tuberculin testing in patients with active pulmonary tuberculosis

OBJECTIVE

The proportion of tuberculin reactors in a population and the intensity of tuberculin reactions have been shown to increase with increasing exposure to mycobacterial infection, eg, repeated BCG immunization. These observations suggested that tuberculin reactivity would become uniformly high in individuals with a high mycobacterial load who did not have a known cause of anergy. Since tuberculin reactivity has been measured to evaluate the possible genetic regulation of responses to mycobacteria in humans, it is important to study its behavior under conditions of ongoing, maximal exposure to mycobacteria. In the present study, we determined the mean size of tuberculin reactivity in BCG-immunized and unimmunized patients with pulmonary tuberculosis of recent onset, and the stability of tuberculin reactions during and after treatment of pulmonary tuberculosis.

METHOD

Serial tuberculin testing was performed on patients with newly diagnosed active pulmonary tuberculosis diagnosed over a period of 2 years at the National Institute for Respiratory Diseases in Santiago, Chile. The first tuberculin test was performed at the time of diagnosis in 58 patients. Repeated tuberculin testing was performed 2 weeks later in 15 patients with initial reaction sizes < 15 mm. Four additional tuberculin tests were performed, one each at 3-months intervals in 42 patients regardless of the size of the initial tuberculin reaction.

RESULTS

Tuberculin reactions at entry had a unimodal distribution in patients both with and without BCG scars (14.8 +/- 5.0 mm and 16.5 +/- 5.2 mm, respectively). A second tuberculin test in patients with initial reaction sizes < 15 mm showed a moderate, statistically significant increase in the mean reaction size (PPD1: 10.1 +/- 3.2 mm; PPD2: 11.9 +/- 4.8 mm). Repeated tuberculin testing over 1 year revealed no significant changes in reaction size. The mean reaction sizes were 15.8 +/- 5.0 mm at entry, 15.5 +/- 5.4 mm at 3 months, 17.2 +/- 5.2 mm at 6 months, 17.0 +/- 5.1 mm at 9 months, and 16.7 +/- 54 mm at 12 months. The standard deviation of a random observation within patients was 5.3 mm. The largest variations due to increased reactivity after 6 months of treatment were observed in patients with reaction < 15 mm at entry compared with hyperergic patients, and in BCG-immunized patients compared to unimmunized patients.

CONCLUSIONS

In the presence of an ongoing mycobacterial infection, patients without anergizing conditions express a tuberculin reactivity that is relatively constant during and after treatment of pulmonary tuberculosis. The size and stability of the reactions seem to be determined by individual conditions that include the tuberculin reactivity at the time of diagnosis and the BCG immunization status.

Four-stage tuberculin testing in elderly subjects induces age-dependent progressive boosting

We administered four sequential tuberculin skin tests (5 TU, PPD) with intervals of one week to 223 subjects older than 65 years of age to evaluate whether elderly subjects demonstrated progressive boosting. Indurations of at least 10 mm with increases of at least 6 mm (over the previous test) were considered significant reactions, and these were found in 29 percent of the subjects after test 1, in 43 percent after test 2, in 53 percent after test 3, and in 57 percent after test 4 (p less than 0.05), ie, only about 50 percent of all the positives were detected after the first test. The percentage of positive reactors was inversely related to age (p less than 0.001), yet this age-dependent difference decreased with increasing number of tests. For the 65- to 74-year-old age group, 44 percent reacted positively after the first test and after three tests almost a plateau of 65 to 70 percent positive reactors was reached, suggesting that a minority only of about 30 to 35 percent of these geriatric patients might have outlived their bacilli or were never infected. For the 75- to 84-year-old age group, 24 percent reacted after the first test and 55 percent reacted after the fourth one. For the older than 85-year-old age group, 19 percent positive reactors were found after the first test and 46 percent were found after the fourth test, without clear-cut leveling off toward a plateau value, suggesting that additional tests would induce further boosting. Mean diameters of positive reactions were 15 to 24 mm, and were mostly at least 12 mm larger than in the previous tests. These data support the hypothesis that the negative tuberculin reaction, which is often found in elderly subjects, is mainly due to the failing immune response to tuberculin antigen that can be restored progressively by repeated administrations. These findings, furthermore, emphasize that especially in elderly, care should be taken not to interpret a boosting reaction as a conversion and especially that neither a two-step testing as recommended by the ATS and CDC (Am Rev Respir Dis 1990; 142:723-35) nor even a four-step testing may suffice to detect all positives in this type of population.

Tuberculosis in long-term care facilities

Persons age 65 and over constitute the largest reservoir ofMycobacterium tuberculosisinfection in the United States today. During 1987, 6,150 tuberculosis cases were reported among this high-risk group. These cases represent 27% of the total US tuberculosis morbidity, although this age group constitutes only 12% of the US population. Tuberculosis case rates in the United States are higher among the elderly (20.6 per 100,000) than among all other age groups (average 9.3 per 100,000).

More Americans live in nursing homes than in any other type of residential institution; on any given day approximately 5% of all elderly persons are living in a nursing home. Elderly nursing home residents are at greater risk for tuberculosis than elderly persons living in the community. In a Centers for Disease Control (CDC)-sponsored survey of 15,379 routinely-reported tuberculosis cases from 29 states, 8% of the 4,919 cases that occurred among elderly persons occurred among residents of nursing homes. The incidence of tuberculosis among nursing home residents was 39.2 per 100,000 person years, whereas the incidence of tuberculosis among elderly persons living in the community was 21.5 per 100,000. The observed rate of tuberculosis among nursing home employees was three times the rate expected in employed adults of similar age, race and sex (CDC, unpublished data).