Detecting Mycobacterium tuberculosis Infection in Children Migrating to Australia

In 2015, Australia updated premigration screening for tuberculosis (TB) disease in children 2–10 years of age to include testing for infection with Mycobacterium tuberculosis and enable detection of latent TB infection (LTBI). We analyzed TB screening results in children <15 years of age during November 2015–June 2017. We found 45,060 child applicants were tested with interferon-gamma release assay (IGRA) (57.7% of tests) or tuberculin skin test (TST) (42.3% of tests). A total of 21 cases of TB were diagnosed: 4 without IGRA or TST, 10 with positive IGRA or TST, and 7 with negative results. LTBI was detected in 3.3% (1,473/44,709) of children, for 30 applicants screened per LTBI case detected. LTBI-associated factors included increasing age, TB contact, origin from a higher TB prevalence region, and testing by TST. Detection of TB and LTBI benefit children, but the updated screening program’s effect on TB in Australia is likely to be limited.     

Tuberculosis transmission in a renal dialysis center--Nevada, 2003

Among persons with chronic renal failure, infection with Mycobacterium tuberculosis is more likely to progress to tuberculosis (TB). Chronic renal failure is an immunocompromising condition associated with cutaneous anergy, which can result in a false-negative tuberculin skin test (TST) result. In 2003, a health-care worker (HCW) (i.e., a hemodialysis technician) in an outpatient renal dialysis center in Nevada became ill with pulmonary TB, exposing more than 400 patients and other employees. The HCW had a previous positive TST result but never received treatment for TB infection. This report summarizes the results of a contact investigation, which suggested that the HCW had transmitted M. tuberculosis to 29 patients and 13 employees. The findings underscore the need for TB screening and treatment of TB infection for all HCWs and patients at high risk.     

2～14岁赴美移民申请人结核病筛查结果分析

〔目的〕对2~14岁赴美移民申请人结核病筛查的结果进行分析,为早期发现潜伏结核感染、肺结核患者及结核病防控提供参考依据。〔方法〕对2009年7月—2010年3月期间在广东国际旅行卫生保健中心体检的2747名2~14岁赴美移民申请人进行结核病筛查,所有申请人均进行结核菌素皮试(TST);若TST≥10mm或申请人有疑似结核的体征或症状,应进行X线胸片检查;若胸片所见疑似结核或有疑似结核的体征或症状的,进行结核分枝杆菌实验室检测。〔结果〕TST皮试结果显示阳性率为47.40%,阴性率52.60%,其中中度阳性者624名,占总人数的22.72%,强阳性者25名,占总人数的0.91%。阴性率随年龄增长逐渐下降,阳性与中度阳性率随年龄增长逐渐上升(P0.001)。649名TST≥10 mm者胸片检查结果发现,疑似结核病患者8人,其中非领养儿童1例,领养儿童7例。结核分枝杆菌实验室检测结果发现,8例疑似肺结核患者中,1例为耐多药结核患者。〔结论〕加强儿童,特别是生活条件和营养条件差的儿童结核病的筛查,提高卡介苗覆盖率及接种质量对于儿童肺结核的防控具有重要意义。     

Tuberculosis contact tracing among children and adolescents, Brazil

OBJECTIVE: To detect tuberculosis (TB) disease or infection among contacts of pulmonary TB patients. METHODS: Cross-sectional study in a Primary Healthcare unit in Rio de Janeiro (Brazil) with 184 child and adolescent contacts of pulmonary TB patients between March 1995 and March 1997. Subjects underwent clinical evaluation, chest radiographs, and tuberculin skin tests (TST); sputum smears were performed whenever possible. TB cases found were submitted to treatment and infected patients to chemoprophylaxis. Tuberculin converters, who tested positive for TST eight weeks after an initial negative result, received chemoprophylaxis. RESULTS: The sample included 98 boys and 86 girls; age ranged from 0 to 15 years; 26.9% were malnourished according to the Gomez criteria. Concerning the source of infection, 170 cases (92.4%) had household contacts, of which 66.5% were the child's parents. BCG vaccination was verified in 98.4% of children, and 14.7% of children had been revaccinated. Strong TST reactions were observed in 110/181 children. Seventy-six children (41.3%) were considered as infected by M. tuberculosis and 25 cases (13.6%) of TB were detected, of which seven (28%) were asymptomatic. There was greater occurrence of disease when the contact lived with more than one source of infection (p=0.02). CONCLUSIONS: The detection of TB disease and infection was high in the studied population. Contact control must be emphasized, for it allows for the diagnosis of TB in children who are still asymptomatic, in addition to identifying infected subjects who may profit from chemoprophylaxis.     

Performance of an interferon-gamma release assay for diagnosing latent tuberculosis infection in children

Newly developed interferon-gamma release assays have become commercially available to detect tuberculosis (TB) infection in adults. However, little is known about their performance in children. We compared test results between the QuantiFERON-TB Gold test (QFT) and tuberculin skin test (TST) in young children living with pulmonary TB patients in Cambodia. Of 195 children tested with both QFT and TST, the TST-positive rate of 24% was significantly higher than the QFT-positive rate of 17%. The agreement between the test results was considerable (kappa-coefficient 0.63). Positive rates increased from 6% to 32% for QFT and from 15% to 43% for TST, according to the sputum smear grades of the index cases. The presence of Bacille Calmette-Guérin (BCG) scars did not significantly affect the results of TST or QFT in a logistic regression analysis. In conclusion, QFT can be a substitute for TST in detecting latent TB infection in childhood contacts aged 相似文献   

In-hospital contact investigation among health care workers after exposure to pulmonary tuberculosis in an intermediate tuberculosis prevalence area: A prospective study

We carried out in-hospital contact investigations of patients with pulmonary tuberculosis and analyzed the prevalence of latent tuberculosis infection (LTBI) among health care workers (HCWs) after TB exposure. A prospective study was conducted of 872 HCWs who were exposed to 55 index cases diagnosed with active pulmonary TB. HCWs after TB exposure were evaluated both TST and chest X-ray at the time of enrollment and 12 weeks after exposure; 625 HCWs (71.6%) underwent both initial assessments; 41 HCWs (6.6%) had a positive TST result. After 12 weeks, 71.1% of HCWs with initial negative TST (n = 415) underwent a second assessment. Ten HCWs had TST conversion. One HCW (0.2%) developed active pulmonary TB. In multivariable analysis, age over 30 years was associated with TST conversion (p = .02). Point prevalence of latent TB was 6.6%, and incidence of LTBI was estimated as 2.4 per 100 HCWs. Strict infection control measures should be emphasized in intermediate TB-burden, BCG-vaccinated countries, especially in HCWs with high risk for TB exposure.     

Is tuberculin skin testing useful to diagnose latent tuberculosis in BCG-vaccinated children?

BACKGROUND: The tuberculin skin test (TST) is the most commonly used tool to detect infection with Mycobacterium tuberculosis. We sought to determine whether tuberculin skin testing is useful to detect latent infection by M. tuberculosis in a population that was vaccinated with the Bacille Calmette Guérin (BCG) vaccine. METHODS: We performed a cross-sectional study during October 2000-February 2001, enrolling first and sixth graders from a random, stratified sample of public elementary schools in Orizaba, Veracruz, Mexico. We assessed the relationship between sociodemographic and epidemiological information, BCG scars, and TST reactivity. RESULTS: There were 858 children enrolled in the study with a completed questionnaire and TST result. The prevalence of a positive TST result (> or =10 mm) was 12.4%. Controlling for BCG scar, age, and other characteristics, close contact with pulmonary tuberculosis patients (odds ratio 6.56, 95% confidence interval 2.05-21.07, P = 0.001) was independently associated with TST reactivity. CONCLUSIONS: TST results helped identify children in a BCG-vaccinated population who had recent exposure to persons with pulmonary tuberculosis, were probably infected with M. tuberculosis, and could benefit from treatment for their latent tuberculosis infection.     

Tuberculosis among adult visitors of children with suspected tuberculosis and employees at a children's hospital.

OBJECTIVE: Few children with tuberculosis (TB) have communicable disease, and most do not require isolation within the hospital. However, parents or adult visitors with unrecognized pulmonary TB may be a threat to hospital staff and other patients. We prospectively evaluated adults accompanying children hospitalized for suspected TB at a children's hospital to determine the frequency of undiagnosed, potentially contagious disease. METHODS: From 1992 to 1998, chest radiographs were obtained from adult caretakers accompanying 59 consecutive children admitted to Texas Children's Hospital with suspected TB. A child and his or her family were placed under Airborne Precautions only if the child or the accompanying adult exhibited characteristics of potentially contagious disease. Annual rates of tuberculin skin test conversion in hospital employees were obtained for the same period. RESULTS: Of the 105 screened adults, 16 (15%) had previously undetected pulmonary TB. These adults were associated with 14 (24%) of the 59 children. In all instances in which the adult was the patient's parent, he or she was the source of infection to the child. Only 8 (13.5%) of the 59 children required isolation. Tuberculin skin test conversion from a negative to a positive reaction occurred in 127 employees (8 per 1,000 employee-years at risk). Only 4 of these 127 employees performed activities involving direct patient contact. None was in contact with families with a known potentially contagious adult or pediatric patient. CONCLUSIONS: The risk of infection of healthcare workers from pediatric patients with primary TB appeared to be minimal, and most children with TB did not need isolation. Infection control efforts should be focused on accompanying adults and adult visitors.     

Tuberculin skin test conversion among medical students at a teaching hospital in Rio de Janeiro, Brazil.

OBJECTIVE: To describe the cumulative incidence of and risk factors for tuberculosis (TB) infection among medical students. DESIGN: In 1999, a cohort study of medical students with negative results (induration < 10 mm) on tuberculin skin test (TST) was performed. Students who had undergone two-step testing in 1998 were retested. SETTINGS: University and teaching hospital and referral center for TB and acquired immunodeficiency syndrome, and the Health Sciences Building of the Medical School of the Federal University of Rio de Janeiro, Brazil. PARTICIPANTS: A sample of 618 consecutive medical students with negative TST results who had been tested 12 months before were approached. Information about sociodemographic characteristics, bacille Calmette-Guérin vaccination history, and potential exposures to TB was obtained using a standardized questionnaire. Four hundred fourteen (67%) students completed the study. Students were at two different levels of their training programs (juniors = no contact with patients; seniors = intensive contact with patients). RESULTS: Of 414 participants, 16 (3.9%; 95% confidence interval, 1.06% to 12.1%) had converted to a positive reaction after 1 year. In a multivariate logistic regression analysis, higher level of clinical training was confirmed to be an independent factor associated with TST conversion (odds ratio, 4.77; 95% confidence interval, 1.01 to 22.46; P= .048). CONCLUSION: Senior medical students are at increased risk of Mycobacterium tuberculosis infection in this setting. Therefore, a program of routine tuberculin skin testing and specific TB infection control guidelines are needed for this population.     

Implementation of an Interferon-Gamma Release Assay to Screen for Tuberculosis in Refugees and Immigrants

Despite increased use and accuracy of interferon-gamma release assays to detect latent tuberculosis infection (LTBI) in foreign-born arrivals in the United States, risk characteristics associated with positive results are not well characterized. We conducted a retrospective record review of 541 refugees and immigrants screened for LTBI with QuantiFERON^®-TB Gold In-Tube (QFT-IT) at the Spokane Public Health Clinic from January 2, 2008, through June 5, 2009. Overall, 24 % of the arrivals had a positive QFT-IT, with the greatest frequency of positive results occurring in arrivals from Liberia (100 %) and Bhutan (39 %). More than the expected number of Burmese had indeterminate QFT-IT results. A positive QFT-IT was associated with age, race, ethnicity, and extent of TB burden in the country of origin. QFT-IT is useful to screen for LTBI in foreign-born arrivals, particularly middle-aged adults from high-burden countries. However, the QFT-IT may not yield meaningful results in groups with significant immunocompromise.     

Preventing tuberculosis among HIV-infected persons: a survey of physicians' knowledge and practices

BACKGROUND: Guidelines exist for screening, diagnosing, and preventing tuberculosis (TB) among HIV-infected persons, but their application and utility are unknown. METHODS: We conducted a survey of knowledge and practices among 1,300 physicians in the San Francisco Bay area to assess their practices towards TB among HIV-infected persons. RESULTS: Of 630 respondents, 350 (56%) provided care for HIV-infected persons. Thirty-four percent of the respondents had seen the most recent guidelines for preventing tuberculosis among HIV-infected persons; 65% routinely provide information to HIV-infected patients about the risks of exposure to Mycobacterium tuberculosis; 39% provide annual tuberculin skin testing (TST) to HIV-infected patients without a history of a positive test; 86% knew that >/=5-mm induration is considered a positive TST result in HIV-infected persons; and 47% provide a 12-month regimen of chemoprophylaxis for HIV-infected persons who have a positive TST but not active tuberculosis. Physician specialty and experience with HIV-infected persons were not strongly correlated; experience was a better predictor of correct knowledge and practices. CONCLUSIONS: Many physicians were not aware of the standards of care for preventing tuberculosis among HIV-infected patients, even in a geographic area with a high prevalence of M. tuberculosis and HIV.     

Latent tuberculosis in nursing professionals of a Brazilian hospital

Tuberculosis (TB) is considered an occupational disease among health-care workers (HCWs). Direct contact with TB patients leads to an increased risk to become latently infected by Mycobacterium tuberculosis. The objective of this study is to estimate the prevalence of latent M. tuberculosis minfection among nursing professionals of a hospital in Rio Grande do Sul, Brazil, assessed by tuberculin skin test (TST). From November 2009 to May 2010, latent M. tuberculosis infection was assessed by TST in 55 nursing professionals. Epidemiological information was collected using a standardized questionnaire. A positive TST result (> or = 10 mm) was observed in 47.3% of the HCWs tested. There was no significant difference in TST positivity when duration of employment or professional category (technician or nurse) was evaluated. The results of this work reinforce the need for control measures to prevent latent M. tuberculosis infection among nursing professionals at the hospital where the study was conducted.     

应用酶联免疫斑点法快速诊断儿童结核分枝杆菌感染的研究

目的:探讨基于ESAT-6和CFP-10抗原肽的酶联免疫斑点技术(Enzyme-link immunospot essay,ELISPOT)在临床实践中诊断儿童结核分枝杆菌感染的临床价值。方法:应用ELISPOT技术检测14例确诊的儿童肺结核病例和16例健康儿童对照的外周血单个核细胞的INF-γ,同时对所有研究对象实施结核菌素皮肤实验(Tuberculin Skin Test,TST),探讨ELIS-POT技术在快速诊断儿童结核分枝杆菌感染的临床应用价值。结果:ELISPOT灵敏度为85.7%(95%CI:60.1～95.0),特异度为93.8%(95%CI:71.7～98.9)。TST灵敏度为71.4%(95%CI:45.4～88.3),特异度为56.3%(95%CI:33.2～76.9)。ELISPOT的灵敏度高于TST,但无统计学意义(P>0.05)。ELISPOT的特异度显著高于TST(P<0.05)。ELISPOT和TST检测结果总一致性较差(κ=0.35)。在活动型结核病组中,ELISPOT和TST一致性较差(κ=0.18),类似地,在对照组中,ELIS-POT和TST一致性也较差(κ=0.16)。不一致的检测结果在病例组中常见ELISPOT阳性而TST阴性(3例),而在对照组中常见于ELISPOT阴性而TST阳性(7例)。结论:ELISPOT诊断儿童活动性结核病准确性高于TST。ELISPOT具有较高的诊断灵敏度和特异度,其特异度不受儿童的卡介苗接种的影响,适合作为临床诊断儿童结核分枝杆菌感染的辅助诊断技术,有助于感染的儿童得到更快速的诊断和治疗。     

Latent Tuberculosis Infection Among Immigrant and Refugee Children Arriving in the United States: 2010

Immigrants and refugees age 2–14 years entering the United States from countries with estimated tuberculosis (TB) incidence rate ≥20 per 100,000 population are screened for TB. Children with TB disease are treated before US arrival. Children with positive tuberculin skin tests (TST), but negative TB evaluation during their pre-immigration examination, are classified with latent TB infection (LTBI) and are recommended for re-evaluation post-arrival. We examined post-immigration TB evaluation and therapy for children arriving with LTBI. We reviewed medical exam data from immigrant children with medical conditions and all refugee children arriving during 2010. Medical examination data were available for 67,334 children. Of these, 8231 (12 %) had LTBI pre-immigration; 5749 (70 %) were re-evaluated for TB post-immigration, and 64 % were retested by TST or IGRA. The pre-immigration LTBI diagnosis was changed for 38 % when retested by TST and for 71 % retested by IGRA. Estimated LTBI therapy initiation and completion rates were 68 and 12 %. In this population, testing with IGRA may limit the number of children targeted for therapy. Increased pre-immigration TB screening with post-immigration follow-up evaluation leading to completion of LTBI therapy should be encouraged to prevent TB reactivation.     

Prevalence of latent tuberculosis infection in German radiologists

Healthcare workers have an increased risk of tuberculosis infection compared with the general population. There have been few attempts to quantify the prevalence of latent tuberculosis infection amongst German healthcare workers, due to inadequacy of the current tuberculin skin test (TST). Therefore, it was our aim to investigate the prevalence of latent tuberculosis in this cohort using a tuberculosis-specific ELISpot (T-SPOT.TB) test and to compare the performance of this test to that of the TST. Ninety-five healthy participants working in departments of radiology were examined by ELISpot, lymphocyte transformation test and TST. For cellular in-vitro tests, tuberculosis-specific peptides and purified protein derivate (PPD) were used as antigens. These tests were combined with a questionnaire on prior tuberculosis exposure. Out of 95 healthcare workers, only one (1%) was defined as positive by T-SPOT.TB, 92 (97%) by PPD-ELISpot, 78 (82%) by PPD-lymphocyte transformation test and 32 (34%) by TST. Multivariate analysis showed that the TST was significantly affected (P<0.0001 and P=0.001, respectively) by foreign birth and prior skin testing. The T-SPOT.TB test results were independent of foreign birth, prior skin testing and prior vaccination against tuberculosis. In contrast to the TST, T-SPOT.TB appears to be an accurate and useful tool to track tuberculosis infection in this at-risk group. With only one of 95 participants having acquired latent tuberculosis, these preliminary results argue for a low incidence of latent tuberculosis in German radiologists.     

Evaluation of tuberculin skin testing in tuberculosis contacts in Victoria,Australia, 2005–2013

Aim: To review the programmatic use of the tuberculin skin test (TST) following tuberculosis (TB) exposure in Victoria, Australia.Methods: A retrospective review of data collected for public health surveillance was performed to identify contact demographic factors, including bacille Calmette-Guérin (BCG) status and age and outcomes of TST.Results: Contact tracing was performed for 15 094 people, of whom 13 427 (89.0%) had a TST performed. The TST was positive in 31.4% (95%CI 30.6–32.2) of all contacts, and 48.8% of contacts born outside of Australia. Amongst contacts who were TST-negative at baseline, the conversion rate following exposure was 14.8%. Conversion was most common in those aged 45–54 years, with <12% positivity in both the youngest (<5 years) and oldest (⩾65 years) age groups. Active TB developed in 1.1% of all contacts. Contacts aged <5 years had the highest risk of developing active TB following exposure (3.8%), while low risk was seen in those aged ⩾65 years (0.3%).Conclusion: Overall, contact tracing and TST in this setting appear to yield a high proportion of people at risk for the development of active TB. The yield of testing in some groups, particularly those aged ⩾65 years, was low, and investigation of alternative strategies should be considered.     

A Quantitative Benefit-Risk Analysis of Isoniazid for Treatment of Latent Tuberculosis Infection Using Incremental Benefit Framework

BackgroundWe undertook a quantitative benefit-risk analysis of a targeted isoniazid (INH) therapy for latent tuberculosis (TB) infection for different groups of contacts of active TB cases.MethodsWe developed a decision-analytic model to compare the treatment of latent TB infection in subgroups of contacts to no treatment over a 6-year time horizon in a Canadian setting. Contacts were stratified into 32 groups on the basis of five binary variables: type of contact (close or casual), tuberculin skin test (TST) results (positive or negative at 5 mm cutoff), Bacillus Calmette-Guérin vaccination status, place of birth (foreign- or Canadian-born), and age group (cutoff 35 years). Risk of TB reactivation was calculated for each subgroup from a longitudinal registry of contacts, adjusted for several potential confounders and comorbid conditions. We calculated the quality-adjusted life-years gained because of delayed or prevention of active TB via treatment of latent TB infection versus quality-adjusted life-years lost because of the adverse events to INH.ResultsA targeted policy based on adopting INH therapy only in subgroups with positive expected incremental net health benefit resulted in a different treatment decision than the current guidelines in five subgroups comprising 3.9% of the contacts. Namely, the targeted policy comprised no INH therapy in casual contacts with a positive vaccination history even with a positive TST result and INH therapy in foreign-born close contacts younger than 35 years even with a negative TST result.ConclusionsFrom a benefit-risk viewpoint, INH treatment of contacts should be tailored on the basis of risk assessment algorithms that consider a range of factors at the time of screening.     

Mycobacterium tuberculosis infection in First Nations preschool children in Alberta: implications for BCG (bacille Calmette-Guérin) vaccine withdrawal

BACKGROUND: On April 1, 2004, BCG (bacille Calmette-Guérin), a tuberculosis (TB) control vaccine, was discontinued in all but four high-risk communities in Alberta. To confirm the safety of vaccine withdrawal, and for future planning, the annual risk of infection (ARI) was determined in preschool First Nations children. METHODS: First Nations children born into reserve communities in Alberta between April 1, 1998 and March 31, 2004, and still living on reserve in 2004-2005, were identified. Health centre TB histories were validated by cross-referencing the birth cohort with the provincial TB Registry. Children that were not BCG vaccinated and not known to be tuberculin skin test (TST) positive underwent a TST. Birth cohort children were grouped as follows: (i) BCG vaccinated; (ii) BCG non-vaccinated, no TST; (iii) BCG non-vaccinated, TST; (iv) BCG vaccination status unknown. The ARI was calculated and the age and community characteristics of the groups were compared. RESULTS: There were 8447 children in the 6-year birth cohort, 4699 (55.6%) vaccinated, 2696 (31.9%) non-vaccinated, and 1052 (12.5%) whose vaccination status was unknown. Of the non-vaccinated children, 1921 (71.3%) were tested and only 2 were TST positive. No other TST positive, BCG non-vaccinated children were identified in the TB Registry cross-match. The prevalence of infection in 2004-2005 was 0.1% and the ARI was 0.03%. The community risk of TB exposure was comparable in tuberculin-tested and non-tested BCG non-vaccinated children. CONCLUSION: In low BCG-uptake First Nations communities in Alberta, the ARI is low and it is safe to withdraw BCG.     

Limited Utility of Name-Based Tuberculosis Contact Investigations among Persons Using Illicit Drugs: Results of an Outbreak Investigation

Persons named by a patient with tuberculosis (TB) are the focus of traditional TB contact investigations. However, patients who use illicit drugs are often reluctant to name contacts. Between January 2004 and May 2005, 18 isoniazid-resistant TB cases with matching Mycobacterium tuberculosis genotypes (spoligotypes) were reported in Miami; most patients frequented crack houses and did not name potentially infected contacts. We reviewed medical records and reinterviewed patients about contacts and locations frequented to describe transmission patterns and make recommendations to control TB in this population. Observed contacts were not named but were encountered at the same crack houses as the patients. Contacts were evaluated for latent TB infection with a tuberculosis skin test (TST). All 18 patients had pulmonary TB. Twelve (67%) reported crack use and 14 (78%) any illicit drug use. Of the 187 contacts evaluated, 91 (49%) were named, 16 (8%) attended a church reported by a patient, 61 (33%) used a dialysis center reported by a patient, and 19 (10%) were observed contacts at local crack houses. Compared to named contacts, observed contacts were eight times as likely to have positive TST results (relative risk = 7.8; 95% confidence interval = 3.8–16.1). Dialysis center and church contacts had no elevated risk of a positive TST result. Testing observed contacts may provide a higher yield than traditional name-based contact investigations for tuberculosis patients who use illicit drugs or frequent venues characterized by illicit drug use.     

Validity of using tuberculin skin test erythema measurement for contact investigation during a tuberculosis outbreak in schoolchildren previously vaccinated with BCG

BACKGROUND: Few studies have examined the validity of administering tuberculosis control measures based on tuberculin skin test (TST) erythema measurement. The present study aimed to clarify the relationship between the erythema and the induration seen following TST and to evaluate the validity of diagnosing tuberculosis infection based on the erythema following TST in school-aged contacts who had been vaccinated with bacillus Calmette-Guérin (BCG) in infancy. METHODS: A 56-month longitudinal study from January 1999 through September 2003 followed 566 junior high school students in Kochi City who were contacts of an infectious tuberculosis case. To evaluate the diagnostic accuracy of the erythema and induration following TST of the contacts, false-positive and false-negative TST results were noted. RESULTS: The natural logarithm of the erythematous response size was linearly related to the induration size. When the size of the erythematous response was used to determine the presence of tuberculosis infection, the proportion of infected children increased with increasing exposure to the index case. When the TST results in the contact investigation were interpreted together with the change in the size of the erythematous response from that observed at the regular school-entry checkup, false positive test results were avoidable among the students who had a large erythematous response after the contact investigation TST, but whose response was only slightly larger than their erythematous response following the school-entry TST. Among the students whose TST results were negative, 1.9% developed tuberculosis. CONCLUSION: Both erythema and induration measurement were equally effective for identifying tuberculosis infection in schoolchildren vaccinated with BCG.