Two-step tuberculin skin test in nurse students and hospital employees

Booster phenomenon (recall effect) of tuberculin skin test, which disturbs diagnosis of tuberculous infection, is prevalent among BCG vaccinated population. We retested 34 nurse students whose initial tuberculin reaction was smaller than 30 mm by erythema (Group A) and 53 hospital employees whose initial reaction was smaller than 20 mm by erythema (Group B). Among the people whose diameter of erythema was less than 10 mm by the first test, 88 percent (8/9) of group A and 43% (6/14) of group B showed reaction 10 mm < or = by erythema and among those whose induration was < 10 mm, 54% (6/11) of group A and 48% (12/25) of group B showed reaction 10 mm < or = in the second testing. Mean and standard deviation of [the difference between the diameter of the 2nd and the 1st testing] was +7.3 +/- 11.8 mm in group A, +9.8 +/- 11.1 mm in group B by erythema and +2.6 +/- 5.9 mm in group A, +2.9 +/- 5.1 mm in group B by induration. These results indicate that booster phenomenon is highly prevalent among the tested group and there can be no appropriate criteria to distinguish new infection and booster phenomenon. Though two-step tuberculin skin test is recommended to get rid of booster phenomenon. Only a little is known about the value of this test to diagnose new infection in Japanese population, majority of whom being BCG vaccinated. Further investigations are required to apply two-step tuberculin skin test for diagnosis of new infection among hospital employees and health care workers in Japan.     

Tuberculin reactivity in adult BCG-vaccinated subjects: a cross-sectional study.

INTRODUCTION: Interpretation of the tuberculin skin test (TST) may be complicated by prior bacille Calmette-Guérin (BCG) vaccination. The skin reaction to the vaccination interferes with the management of individuals who may be infected with Mycobacterium tuberculosis. OBJECTIVE: To discriminate between TST reactions due to infection and those due to vaccination in subjects with unknown BCG status. METHODS: Among 60200 subjects tested with 5TU PPD for screening purposes, 4987 contacts of infectious TB cases (Group A), 4962 BCG-vaccinated subjects (Group B) and 5000 subjects from the general population (Group C) were sampled. The frequencies of TST cut-off diameters were calculated for the three groups using a logistic regression model. The frequency of positive subjects in each group and the sensitivity, specificity and predictive values were also computed by means of these cut-offs. RESULTS: The risk of being a contact versus BCG-vaccinated increases 2.43-fold with every mm of TST diameter. The 11 mm cut-off point seems to be the best discriminating value. CONCLUSIONS: Using the traditional 10 mm cut-off, we can consider all vaccinated subjects with a positive TST to be infected. The TST remains a valuable tool for the evaluation of household contacts and suspected cases of tuberculosis in BCG-vaccinated subjects and in populations with high vaccination coverage.     

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.     

False-positive tuberculin skin tests: what is the absolute effect of BCG and non-tuberculous mycobacteria?

BACKGROUND: Despite certain drawbacks, the tuberculin skin test (TST) remains in widespread use. Important advantages of the TST are its low cost, simplicity and interpretation based on extensive published literature. However, TST specificity is reduced by bacille Calmette-Guérin (BCG) vaccination and exposure to non-tuberculous mycobacteria (NTM). METHODS: To estimate TST specificity, we reviewed the published literature since 1966 regarding the effect of BCG vaccination and NTM infection on TST. Studies selected included healthy subjects with documented BCG vaccination status, including age at vaccination. Studies of NTM effect had used standardised NTM antigens in healthy subjects. RESULTS: In 24 studies involving 240,203 subjects BCG-vaccinated as infants, 20,406 (8.5%) had a TST of 10+ mm attributable to BCG, but only 56/5639 (1%) were TST-positive if tested > or =10 years after BCG. In 12 studies of 12,728 subjects vaccinated after their first birthday, 5314 (41.8%) had a false-positive TST of 10+ mm, and 191/898 (21.2%) after 10 years. Type of tuberculin test did not modify these results. In 18 studies involving 1,169,105 subjects, the absolute prevalence of false-positive TST from NTM cross-reactivity ranged from 0.1% to 2.3% in different regions. CONCLUSIONS: The effect on TST of BCG received in infancy is minimal, especially > or =10 years after vaccination. BCG received after infancy produces more frequent, more persistent and larger TST reactions. NTM is not a clinically important cause of false-positive TST, except in populations with a high prevalence of NTM sensitisation and a very low prevalence of TB infection.     

The protective effect of BCG vaccination as indicated by autopsy studies

In a detailed study of the pathology of tuberculous infection made in Finland in 1961, tuberculous foci were found at autopsy in 61 of 67 non-vaccinated subjects and in 35 of 83 BCG-vaccinated subjects, all of whom had died between the ages of 1 and 45 years (with 2 exceptions from causes other than tuberculosis). In the present note on the same material, national information on tuberculin sensitivity and tuberculosis mortality has been used to calculate the risk of tuberculous infection in Finland at different times and ages during the lifetime of these subjects. From these risks of infection in Finland it was estimated that 63 or 64 of the non-vaccinated subjects had been infected during their lifetime and that between 25 and 31 of the BCG-vaccinated subjects were expected to have been naturally infected (had they not been vaccinated) between the time of vaccination and death. It is concluded that virtually all tuberculous infections in unvaccinated subjects lead to pulmonary foci, which are demonstrable at autopsy. Further, the same appears to be so in vaccinated subjects; there is no evidence to support the suggestion that in man BCG vaccine can prevent the establishment of infection in an exposed subject. The effects of BCG (as demonstrated in the earlier paper) appear to be confined to limiting the multiplication and dissemination of the bacilli and the development of lesions following infection.     

The effect of bacille Calmette-Guérin vaccination at birth on tuberculin skin test reactivity in Ugandan children.

SETTING: In Uganda, bacille-Calmette Guerin (BCG) vaccination coverage at birth is between 82 and 84%. OBJECTIVE: To evaluate the effect of neonatal BCG vaccination on tuberculin skin test positivity in Ugandan children exposed to infectious cases. DESIGN: As part of an ongoing prevalence study of household contacts of new tuberculosis cases, 365 children were evaluated to determine if BCG vaccination at birth had an impact on tuberculin skin testing. The children were classified as contacts (179) and non-contacts (186) depending on the presence of a sputum acid-fast bacilli (AFB) smear-positive adult tuberculosis case in the household. RESULTS: Regardless of prior BCG vaccination, children exposed to a smear-positive adult were more likely to have a positive skin test (purified protein derivative >5mm) (68% versus 36%, P < 0.01). BCG-vaccinated children below 1 year of age without a known household contact with active tuberculosis had a lower frequency of tuberculin skin reactions (29%) compared to their counterparts in the contact households (65%, P = 0.031). CONCLUSION: BCG vaccination at birth had no important effect on the interpretation of the tuberculin skin test reactivity in this group of Ugandan children. The tuberculin skin test remains a valuable tool for the evaluation of household contacts and suspected cases of tuberculosis in BCG-vaccinated children.     

Avoiding the effect of BCG vaccination in detecting Mycobacterium tuberculosis infection with a blood test.

Bacille Calmette-Guérin (BCG) vaccination can confound tuberculin skin test (TST) reactions in the diagnosis of latent tuberculosis infection (LTBI). The TST was compared with a Mycobacterium tuberculosis (MTB)-specific enzyme-linked immunospot (ELISPOT) assay during an outbreak of MTB infection at a police academy in Germany. Participants were grouped according to their risk of LTBI in close (n = 36) or occasional (n = 333) contacts to the index case. For the TST, the positive response rate was 53% (19 out of 36) among close and 16% (52 out of 333) among occasional contacts. In total, 56 TST-positive contacts (56 out of 71 = 78.9%) and 27 TST-negative controls (27 out of 298 = 9.1%) underwent ELISPOT testing. The odds ratio (OR) of a positive test result across the two groups was 29.2 (95% confidence interval (CI) 3.5-245.0) for the ELISPOT and 19.7 (95% CI 2.0-190.2) for the TST with a 5 mm cut-off. Of 369 contacts, 158 (42.8%) had previously received BCG vaccination. The overall agreement between the TST and the ELISPOT was low, and positive TST reactions were confounded by BCG vaccination (OR 4.8 (95% CI 1.3-18.0)). In contrast, use of a 10-mm induration cut-off for the TST among occasional contacts showed strong agreement between TST and ELISPOT in nonvaccinated persons. In bacille Calmette-Guérin-vaccinated individuals, the Mycobacterium tuberculosis-specific enzyme-linked immunospot assay is a better indicator for the risk of latent tuberculosis infection than the tuberculin skin test.     

Boosted tuberculin skin testing in hemodialysis patients

BACKGROUND: Tuberculosis remains a significant health problem for patients receiving long-term hemodialysis (HD). The tuberculin skin test (TST) is an important method of detecting Mycobacterium tuberculosis infection. Cutaneous anergy decreases the accuracy of the test in these patients. Higher and repeating doses have been mentioned in the immunosuppressed patients. This study examined the significance and frequency of the booster phenomenon in 2-step tuberculin testing of these patients. METHODS: A total of 106 outpatients in a hospital-based HD center in Turkey were screened with 5 and 10 tuberculin units (TU) and Candida antigen. To determine the frequency of booster phenomenon, patients with <10 mm indurations to the initial TST with 5 TU were given a second test with 10 TU, 7 days later. RESULTS: Forty (37.7%) of 106 patients had a significant tuberculin reaction (>or=10 mm) on the initial TST with 5 TU. The booster effect was detected in 16 (24.3%) of 66 patients who had a negative reaction (相似文献   

Tuberculin reactivity in Bacillus Calmette-Guérin vaccinated subjects

Setting: The Centre for Prevention and Control of Tuberculosis in Barcelona, Spain, where the staff appointed to Training Centers are examined.Aims: To check for tuberculin sensitivity due to Bacillus Calmette-Guérin (BCG) vaccine and ascertain its duration.Method: We compared the results of a tuberculin test (TT) on vaccinated and non-vaccinated subjects. The induration diameter and the time elapsed between BCG vaccination and the TT were determined.Results: Of the 2424 vaccinated subjects, 1489 (61.4%) reacted to TT (≥ 5 mm) and of the 3135 non-vaccinated, 905 (28.9%) reacted, a significant difference. Of 1978 subjects vaccinated between 6 and 14 years of age, 63.3% were TT reactors, compared to 23.9% of the 1948 non-vaccinated. Induration diameters ≥ 15 mm amounted to 11% for vaccinated subjects and 8% for those not vaccinated, a significant difference. The time from vaccination to TT was 13–25 years. Of the 446 subjects vaccinated at birth, 237 were reactors (53.1%); of the 887 non-vaccinated subjects of the same age, 154 (17.4%) reacted. Reactors ≥ 15 mm amounted to 40 (9%) for vaccinated subjects and 46 for non-vaccinated (5.2%), a significant difference. The time elapsed between vaccination and TT was 20–25 years. For 124 vaccinated subjects with a previous negative TT, a second test was positive for 87 (70.2%), and for 257 non-vaccinated it was positive for 64 (24.9%). The difference is due to a booster effect.Conclusions: BCG vaccination at birth and for school age children causes a reactivity to tuberculin which persists for 20 to 25 years. An induration diameter of ≥ 15 mm does not exclude a vaccinal origin. For vaccinated subjects with a previous negative TT, it is necessary to exclude the booster effect.     

Results of two-step tuberculin skin test against medical and nursing school students and treatment according to the results of the test]

To assess the risk of tuberculosis infection in medical and nursing school students, tuberculin skin tests were carried out in the two-step manner. The second tuberculin skin test was repeated two weeks later excluding those who were strongly positive in the first test. BCG vaccination was done with the consent of students who showed negative reaction twice. Medical interview and revaluation of prior routine chest radiogram were made on students who were strongly positive. Prophylactic INH medication was considered to those who are at high risk of tuberculosis. Eight hundred thirty eight students underwent the two-step tuberculin skin test, and among them, 771 students showed the positive reaction on the first test (92.0%) which included 58 weakly positive (6.9%), 347 intermediately positive (41.4%) and 366 strongly positive (43.7%) and 2 not-measurable (0.2%), and 65 students were negative (7.8%). The average size of the erythema was 30.9 +/- 18.8 mm on the first test and 37.9 +/- 20.6 mm on the second test. Twenty one students were negative on the second tuberculin skin test, and among them, 15 received BCG vaccination. Out of eight students who were vaccinated with BCG in 1999 and were followed up in the next year, 6 (75.0%) converted to positive. Strongly positive reaction was seen in 28 students (3.3%) and one of them underwent prophylactic medication of INH according to her family history of exposure to tuberculosis.     

Usefulness of QuantiFERON TB-2G in contact investigation of a tuberculosis outbreak in a university

PURPOSE: This study examined the usefulness of QuantiFERON TB-2G (QFT) i.e., a novel technique for detecting tuberculosis infection based on the whole blood interferon-gamma response to specific antigens, in the investigation of a tuberculosis outbreak among university students. SUBJECTS AND METHOD: One university student was diagnosed as smear-positive pulmonary tuberculosis. In order to determine the extent of tuberculosis infection among contact students, tuberculin skin tests and QFT were performed on the close-contact group (220 people), as well as on the non-close-contact group (242 people). RESULTS: Nine students were found to be TB either clinically or on the X-ray screening in the contact investigation. In the close-contact group, the QFT-positive rate was 32.7%. The proportion of those exhibiting tuberculin reactions with erythema diameters of 30 mm or larger was 57.7%. In the non-close-contact group, the QFT-positive rate was only 0.8 %, as expected from the current healthy Japanese youths of this age. In contrast, strong tuberculin reactions with erythema of 30 mm or larger were seen in 18.2% in the latter group, most likely due to the previous history of BCG vaccination. CONCLUSION: QFT was clearly demonstrated to be a useful method for diagnosing tuberculosis infection, especially among subjects who show tuberculin reactivity due to past BCG vaccination. At the same time, the current criteria for the indication of chemoprophylaxis based on the strong tuberculin reaction were considered to be unreliable, causing many subjects with strong reactions to be given unnecessary preventive medications.     

Repeat tuberculin testing in BCG-vaccinated subjects in the United Kingdom. The booster effect varies with the time of reading

The booster effect varies between populations, but has not been studied in the UK. The aim of this study was to investigate the effect of repeat tuberculin tests at 1 wk in BCG-vaccinated healthy subjects (all hospital employees) in the UK; we have assessed whether a booster effect is present 48 and 72 h after injection. Twenty-six subjects received two tuberculin tests (both 10 units) administered by the Mantoux technique-Tests 1 and 2. At Test 2 there was a significant increase in induration at 48 h (mean, 7.8 mm; p < 0.001), no difference at 72 h (mean, 0.2 mm; p = 0.93), and a reduction at 96 h (mean, -4.2 mm; p = 0.02). There were more positive results (> 15 mm induration) at Test 2 compared with Test 1 at 48 h (19 vs. 9, respectively; p = 0.002), but similar numbers at 72 h (11 vs. 10, respectively). These results show that repeat tuberculin testing in this BCG-vaccinated population caused a booster effect that varied with the time of measurement and was maximal at 48 h.     

Prevalence and factors associated with tuberculosis infection among new school entrants, New York City, 1991-1993.

SETTING: New York City public (or state-run) and private schools-elementary and secondary. OBJECTIVE: To describe the prevalence and determine factors associated with positive tuberculin skin tests (TSTs) in school children. DESIGN: Mandatory TST surveys among cohorts of new school entrants for the 1991, 1992 and 1993 school years, of whom birthplace was known for 81%. A positive tuberculin skin test defined as > or =10 mm induration. RESULTS: Of the 298506 new school entrants, 2.1% (6326) were tuberculin test positive. The proportion that was tuberculin test positive was 0.5% (931/199 728) among US-born and 9.2% (3794/41 346) among foreign-born students. Foreign-born (FB) students with a history of BCG vaccination were much more likely to have a positive tuberculin test than US-born students (13.6% vs. 0.5%, odds ratio [OR] = 33.6, 95% confidence interval [CI] 31.7, 35.6), and were more likely to have a positive tuberculin test than FB students with no history of BCG (13.6% vs. 4.4%, OR = 3.4, 95% CI 2.5, 4.6). Older age was independently associated with tuberculin test positivity, except among foreign-born BCG-vaccinated children, in whom the youngest were more likely to have a positive tuberculin test. CONCLUSIONS: Even in the midst of a tuberculosis resurgence such as that experienced by New York City, where tuberculosis cases nearly tripled from 1978 to 1992, the risk of tuberculosis infection among school children remained quite low. Given the reduced predictive value of the tuberculin test among low risk children and the effects of BCG vaccination, many children (especially younger children) with positive tuberculin test results are probably not infected with Mycobacterium tuberculosis. To reduce unnecessary evaluation and treatment, routine tuberculin tests should be administered only to high risk groups such as older children from countries with high rates of tuberculosis.     

Tuberculin skin testing in students of school of nursing]

Tuberculin skin testing in students of the School of Nursing Attached to National Hiroshima Hospital was analyzed. On initial test using 0.05 microgram of PPDs, diameter of erythema in 26.7% of 300 new students were less than 9 mm. Twelve of 24 who were tested by two-step method reacted more than 10 mm on the second test. Twenty-seven non-reactors who were vaccinated with BCG all reacted more than 10 mm after 9 to 16 weeks after vaccination. They might be vaccinated in the past by insufficient technique and better be revaccinated. Thirty-one of 49 students who graduated in 1998 were tested and their reactions were compared with those on entrance or after BCG vaccination. The two tests were spaced 31 to 34 months apart. The reactions were weakened in the cases after BCG vaccination, and in those who were not vaccinated on entrance, only a little booster effect were observed, except in 3 graduates whose reactions were significantly boosted and thought to be infected while in school. As there is considerable variation in tuberculin reactivity after BCG vaccination, diameter of reaction should be kept on personal health record as base line reaction to diagnose tuberculous infection henceforce.     

The booster phenomenon in 2-step tuberculin skin testing of patients receiving long-term hemodialysis

BACKGROUND: Tuberculosis remains a significant health problem for patients receiving long-term hemodialysis (HD). The tuberculin skin test (TST) is an important method for detecting Mycobacterium tuberculosis infection. This study examined the significance and frequency of the booster phenomenon in serial TST of HD patients. METHOD: Fifty-three outpatients in a hospital-based HD center in Turkey were screened for tuberculosis with the TST between August and October 1999. To determine the frequency of booster phenomenon, patients with less than 10 mm indurations to the initial TST were given a second test 7 days later. RESULTS: Nineteen (35.8%) of 53 patients had a significant tuberculin reaction (> or = 10 mm) on the initial TST. The booster effect was detected in 10 (29.4%) of 34 patients who had a negative reaction (< 10 mm) to the initial test. Overall, 29 (54.7%) patients showed a significant reaction on both tests. CONCLUSIONS: These results showed significant rates of TST positivity and the booster effect in this HD center.     

Cost-effectiveness analysis of QuantiFERON-TB 2nd generation used for detection of tuberculosis infection in contact investigations

PURPOSE: QuantiFERON-TB-2nd Generation (QFT) has recently been developed as an accurate tool for detecting tuberculosis infection regardless of past history of BCG vaccination. A cost-effectiveness analysis was made on the usefulness of QFT that was used in the contacts investigation of a group of subject exposed to tuberculosis infection. METHODS: A model was built assuming that a group of youngsters was exposed to an infection source with different degrees of intensity. The distribution of the tuberculin reaction of this group was assumed to be variable according to the history of BCG vaccination and tuberculin testing. Also, the distribution of tuberculin reaction size after the recent exposure is assumed to be different, as has been observed previously. The strategies for investigating this group included giving QFT to subjects having erythema size exceeding 30 mm, 20 mm, and 10 mm as compared with the strategy with the tuberculin test only, or the QFT only. The outcome variables calculated for each strategy were sensitivity and specificity, and predictive values in detecting tuberculosis infection; the number of indications for chemoprophylaxis, the number of tuberculosis patients averted, and the costs incurred in treating tuberculosis patients and chemoprophylaxis cases and testing with tuberculin and QFT were also considered. The sensitivity (specificity) of the QFT employed in the analysis was 89% (98%) based on our observations. RESULTS & CONCLUSION: It was confirmed that the additional use of QFT would greatly reduce the number of indications for chemoprophylaxis cases that have never been infected and that the use of QFT is cost effective in spite of its relatively high unit cost. It will be useful to decide on the eligibility of QFT testing, i.e., the minimal tuberculin reaction size of subjects to whom QFT is given, based on the assumption of pre-exposure distribution of tuberculin reaction size of the group.     

Factors associated with tuberculin reactivity among the foreign-born in Montreal.

Because tuberculosis among the foreign-born is of increasing importance in North America, it has recently been recommended that newly arriving immigrants be tuberculin tested and preventive therapy given to all those with significant reactions. The factors affecting the prevalence of tuberculin reactions were assessed in a community-based tuberculin survey among foreign-born schoolchildren and young adults. Of 1,198 foreign-born who were tuberculin tested, 32.4% had significant tuberculin reactions. False-positive tuberculin reactions due to sensitivity to purified protein derivative (PPD)-B (for Mycobacterium avium) were uncommon and those due to BCG vaccination of importance only among immigrants from countries with low tuberculosis rates. Tuberculin reactions of 10+ mm were associated with tuberculosis rates in the country of origin (p less than or equal to 0.001), age when immigrated (p less than or equal to 0.001), bacillus Calmette-Guérin (BCG) vaccination (p less than or equal to 0.01), and residence in poorer neighborhoods in Montreal (p less than or equal to 0.001), but not with number of years resident in Canada. The booster phenomenon, seen in 16% of those undergoing two-step testing, was most strongly associated with prior BCG vaccination (p less than or equal to 0.001) and also with tuberculosis rates in the country of origin (p less than or equal to 0.08), age of immigration (p less than or equal to 0.01), and number of years resident in Canada (p less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of positive tuberculin skin test with an interferon-gamma-based assay in unexposed children

A false-positive tuberculin skin test (TST) may be a result of T-cell sensitivity due to Bacille Calmette-Guerin (BCG) vaccination or exposure to non-tuberculous mycobacteria, thus leading to unnecessary isoniazid preventive therapy, especially in low-risk populations. Unlike TST, T-SPOT.TB is not confounded by BCG vaccination or exposure to most of the other non-tuberculous mycobacteria, because this assay is based on enumeration of interferon-gamma-secreting T cells in response to Mycobacterium tuberculosis-specific antigens. We compared the TST with T-SPOT.TB with respect to different TST cut-off points in healthy unexposed BCG-vaccinated schoolchildren. A total of 209 children between 6 and 10 years of age with a TST induration of 0 (n = 50), 10 - 14 (n = 45), 15 - 19 (n = 95) and > or =20 mm (n = 19) were enrolled. Among TST-positive subjects, only 26 (23%) were positive with T-SPOT.TB, and T-SPOT.TB was positive in 4, 7, 20 and 42% of children with TST indurations of 0, 10 - 14, 15 - 19 and > or =20 mm, respectively. We suggest that confirmation of a positive TST by the interferon-gamma-based test would reduce unnecessary preventive therapy significantly in healthy unexposed BCG-vaccinated children.     

The frequency profiles of size of two-step tuberculin skin tests with histories of BCG vaccinations and tuberculin tests among hospital employees

In 1998, Prevention Committee of the Japanese Society for Tuberculosis announced guidelines for dealing with nosocomial tuberculosis infections. These guidelines recommended the two-step tuberculin tests (TST) as baseline data for each medical employee when they started to work. If accurate records of previous TSTs are available in addition to baseline data, they are useful to evaluate the presence of tuberculosis infection when they started to work. We therefore studied the frequency profile of size of TST among medical employees in INBA-HITEC Medical Center and discussed methods to improve investigative measures for tuberculosis infection, and prior to skin testing we asked self-reporting questionnaires regarding history of previous BCG vaccinations and TSTs. We expected that their records of previous TSTs were accurately preserved, however, records of previous TSTs reported by medical employees were found to be inaccurate. From two-step TSTs results, the magnitude of booster phenomenon was defined by diameter of erythema and induration. Results demonstrated that the increase of induration size was larger in subjects > or = 41-years-old than in subjects < 41-years-old. Regarding booster phenomenon, no statistically significant differences were detected according to type of duty post. Many subjects with size of TST erythema > or = 30 mm on the first test showed increase erythema > or = 10 mm on the second test. We therefore suggest that the second test be made for those showing reaction size > or = 30 mm on the first test.     

A study on estimating the natural TB infection prevalence in BCG vaccinated regions

The authors analysed the distribution of the sizes of tuberculin reaction of those who have not been BCG vaccinated. The result shows that the proportions of persons with certain tuberculin reactors, greater than or equal to 6mm to greater than or equal to 15mm, greater than or equal to 6mm to greater than or equal to 20mm and greater than or equal to 15mm to greater than or equal to 20mm are relatively stable. Comparing the tuberculin inoculation size in BCG vaccinated group with those of non vaccinated, it shows that the size of tuberculin reactions greater than or equal to 15mm might not be influenced by BCG vaccination. It seems that the number of reactors of greater than or equal to 15mm are able to be used to estimate the prevalence of natural TB infection in BCG vaccinated regions.