A tuberculin skin test survey among Afghan children in Kabul

SETTING

Kabul, Afghanistan, October to November 2000.

OBJECTIVE

To determine the prevalence and the average annual risk of infection with Mycobacterium tuberculosis (ARTI).

METHODS

A cluster sampling method was selected to carry out the survey. Sub-divisions of Kabul's districts were chosen, and door-to-door visits were carried out to register the children. The prevalence of tuberculous infection was determined using a cut-off point to denote infection and mixture analysis. The average ARTI was derived algebraically from the prevalence estimates.

RESULTS

The tuberculin skin test was administered and read in 89% of registered children. Utilising a cut-off point of > or = 8 mm in duration, the estimated prevalence of tuberculous infection was 4.3% and the calculated average ARTI was 0.61%. Using mixture analysis, the average ARTI was estimated to be 0.34% (95% credibility interval 0.23-0.54). This indicates a substantial decrease from the estimated ARTI of 2.55% calculated in the 1963 survey.

CONCLUSIONS

There has been a large decrease in the risk of tuberculous infection in Kabul since the last assessment. The adverse situation in the past decades does not appear to have severely affected the epidemiological situation.

Nontuberculous mycobacterial infection in children: a 2-year prospective surveillance study in the Netherlands

We performed a prospective, 2-year nationwide study to assess incidence and disease characteristics of suspected infections with nontuberculous mycobacteria (NTM) in children, via the Netherlands Pediatric Surveillance Unit. Data for 61 children were reported (median age, 31 months; interquartile range, 22-50 months; female sex, 37 subjects); 2 subjects had an underlying disease. Most children (53 [87%] of 61) had cervical lymph node enlargement, with abscess in 25 (47%) and fistula in 11 (21%). The estimated annual incidence of NTM infection was 77 cases per 100,000 children. In 16 children, the diagnosis was based solely on the results of skin tests with mycobacterial antigens. Cultures were performed in 36 cases and yielded mycobacteria in 27 (75%); Mycobacterium avium was isolated from 18 cultures. Children with a culture positive for mycobacteria did not differ in presentation, complications, or treatment from those whose cultures showed no growth. Thirty children underwent surgery, and chemotherapy was the single treatment in 24 (39%) of the cases. The treatment of localized NTM infection in immunocompetent children by antimycobacterial drugs should be evaluated further.

Acceptance of screening and completion of treatment for latent tuberculosis infection among refugee claimants in Canada

SETTING

Primary care clinic for refugee claimants, Montreal, Canada.

OBJECTIVES

To identify factors linked to the acceptance of the tuberculin skin test (TST), and assess completion of treatment for latent tuberculosis infection (LTBI).

DESIGN

Asylum seekers consulting for a medical complaint or medical immigration examination between February and October 1999 were assessed for eligibility. Personal and clinical information was gathered prospectively by questionnaire. Hospital files were reviewed to assess completion of LTBI treatment.

RESULTS

In our study, 296 subjects (72.4% of 409 eligible) were offered TST, of whom 227 accepted (76.7%). Of these, 49 (24.9%) had a TST > or = 10 mm and 24 (49%) completed 6 months of LTBI treatment. Logistic regression models showed that patients who had never had a TST (OR 3.2, 95%CI 1.34-7.6) or had no temporary exclusion criteria (OR 4.0, 95%CI 1.6-9.9) were more likely to accept TST. Perceiving tuberculosis as a severe disease (OR 0.29, 95%CI 0.09-0.91) and consulting for an immigration examination (OR 0.42, 95%CI 0.18-0.98) was associated with refusal of TST. Increasing age was found to be independently associated with a positive TST (OR 1.06, 95%CI 1.01-1.12). Variability in the proportion of positive results was found between TST readers.

CONCLUSION

This study supports the feasibility of screening refugee claimants for LTBI during medical consultation and of developing organizational links to ensure completion of LTBI treatment.

Risk of infection with Mycobacterium tuberculosis in Malawi: national tuberculin survey 1994

OBJECTIVE

To estimate the annual risk of tuberculosis infection among schoolchildren in Malawi.

METHODS

A school survey was conducted in twelve randomly selected districts in Malawi. Children in standard 1-4 and aged 6-11 years were eligible. Tuberculin skin testing was performed according to World Health Organization/International Union Against Tuberculosis and Lung Disease guidelines.

RESULTS

Of the 17123 eligible children, 80% were tested. Of those tested 79% were read. The prevalence of infection according to various criteria was 9-12% in children without bacille Calmette-Guerin (BCG) scar. The prevalence of reactions of 10 mm or more was lower in girls than in boys, increased with age, and was higher in those with than in those without BCG scar. The annual risk of infection was estimated to be within the range 0.6-1.4%.

CONCLUSION

Annual risk of infection in Malawi was in the order of 1%. This study is expected to provide valuable baseline information for an assessment of the impact of human immunodeficiency virus (HIV) on tuberculosis transmission in Malawi.

[Tuberculin skin test reaction of health-care workers exposed to tuberculosis infection]

OBJECTIVE

The objective of this study was to describe tuberculin skin test (TST) of health-care workers who had had contacts with a tuberculosis patient and to investigate whether the distributions of the size of TST were different by sputum-smear status of index cases and medical procedures done to the patient.

SUBJECTS

Health-care workers who were exposed to tuberculosis infection through contact with patients before diagnosis of tuberculosis were included in this study. Index cases had pulmonary tuberculosis with positive sputum smear and were registered at Sapporo Public Health Office from April 2001 to March 2002. Subjects without past history of BCG (bacilli Calmette-Guerin) vaccinacion were excluded, and final study subjects were 415 (52 male and 363 female, mean age 29.1 years).

METHOD

Characteristics of index cases and contact status were obtained from the registration cards of tuberculosis cases at Sapporo Public Health Office. Subjects were divided into two or more categories by the characteristics of index cases and the contact status. Distributions of TST of the subjects in different categories were compared.

RESULTS

Contacts with patients received tracheal aspiration showed significantly larger TST reaction than contacts with patients not receiving tracheal aspiration. Among contacts with patients showing minimum to moderately positive sputum-smear, TST reaction was significantly larger in contacts with patients received tracheal aspiration (mean diameter of erythema 35.8 mm) than those not receiving tracheal aspiration (24.8 mm). In contrast, among contacts with patients of severely positive sputum-smear, TST reaction was not significantly different between contacts of patients received tracheal aspiration (35.3 mm) and not receiving tracheal aspiration (33.1 mm).

CONCLUSION

TST was significantly stronger in contacts with a tuberculosis patient received tracheal aspiration, which indicates medical procedures such as tracheal aspiration increases the risk of tuberculosis infection in health-care workers.

Tuberculin skin testing underestimates a high prevalence of latent tuberculosis infection in hemodialysis patients

BACKGROUND

Identification of latent Mycobacterium tuberculosis infection in hemodialysis patients is hampered by reduced sensitivity of the established tuberculin skin test. We investigated whether in vitro quantitation of purified protein derivative (PPD)-specific T cells using a rapid 6-hour assay may represent an alternative approach for detecting latent infection.

METHODS

One hundred and twenty-seven hemodialysis patients and 218 control patients (blood donors, health care workers, and control patients) were analyzed. Specific T cells toward PPD and early secretory antigenic target-6 (ESAT-6), a protein expressed in Mycobacterium tuberculosis but absent from M. bovis bacillus Calmette-Guerin (BCG) vaccine strains, were flow cytometrically quantified from whole blood, and results were compared with skin testing.

RESULTS

Compared to blood donors, a high proportion of both health care workers (48.6%) and hemodialysis patients (53.5%) had PPD-specific Th1-type CD4 T-cell reactivity with similar median frequencies of PPD-specific T cells (0.17%; 0.06-3.75% vs. 0.26%; 0.06-4.12%, respectively). In contrast, skin test reactivity was significantly reduced in hemodialysis patients. Whereas 85.7% of control patients with PPD reactivity in vitro were skin test-positive, the respective percentage among hemodialysis patients was 51.4% (P= 0.007). Among individuals with PPD reactivity in vitro, approximately 50% had T cells specific for ESAT-6.

CONCLUSION

Unlike the skin test, measurement of PPD reactivity by in vitro quantitation of PPD-specific T cells was unaffected by uremia-associated immunosuppression. This whole-blood assay may thus be a valuable alternative to skin testing, and detection of ESAT-6-specific T cells could moreover allow distinction of latent M. tuberculosis infection from BCG-induced reactivity to PPD. The assay is well suited for clinical use and may facilitate targeting of preventative therapy in high-risk individuals.

[Analysis of the diagnostic criteria used in childhood tuberculosis in a Cote d'Ivoire hospital]

Based on a retrospective study the authors analyzed the diagnostic criteria used in pediatric department in Yopougon CHU (teaching hospital), from January 1996 to December 2002. Fifty children, aged of 1 month to 15 years, have been studied. The tuberculosis contact was found in 18%. The diagnosis of tuberculosis was accurate in 32% and it was based on presumptive arguments in 68%. The pulmonary examination and pulmonary radiographs seem to be good criteria for the tuberculosis diagnosis. The pulmonary examination found an abnormality in 96%, and the radiographs found a pathological picture in 85% of cases. The skin test was positive in 42%. The Ziehl-Neelsen coloration was used to look for the acid-fast bacilli and it was positive in 41%. But the two last examinations were not reliable in the case of HIV infection. The skin test which is very important for the diagnosis of tuberculosis is often negative among HIV infected children because of their anergy. On the other hand, the Ziehl-Neelsen coloration is based on the recognition of the acid-fast bacillus, which is not specific of the Mycobacterium tuberculosis. In our area the prevalence of HIV/AIDS is high, the atypical pneumonia with Mycobacterium were also frequent and may reveal a wrong positive diagnosis for the tuberculosis diagnosis, as they are also acid-fast bacillus.

Prevalence of tuberculin skin test positivity and conversions among healthcare workers in New York City during 1994 to 2001

OBJECTIVE

To determine the prevalence of and risk factors for tuberculin skin test positivity and conversion among New York City Department of Health and Mental Hygiene employees.

DESIGN

Point-prevalence survey and prospective cohort analysis. Sentinel surveillance was conducted from March 1, 1994, to December 31, 2001.

PARTICIPANTS

HCWs in high-risk and low-risk settings for occupational TB exposure.

RESULTS

Baseline tuberculin positivity was 36.2% (600 of 1,658), 15.5% (143 of 922) among HCWs born in the United States, and 48.5% (182 of 375) among HCWs not born in the United States. There were 36 tuberculin conversions during 2,754 observation-years (rate, 1.3 per 100 person-years). For HCWs born in the United States, the risk for tuberculin conversion was greater in high-risk occupational settings compared with low-risk settings (OR, 5.7; CI95, 1.7-19.2; P < .01). HCWs not born in the United States and those employed at the Office of the Chief Medical Examiner (OCME) were at high risk for baseline tuberculin positivity (OR, 3.2; CI95, 1.7-5.8; P < .001); OCME HCWs (OR, 4.7; CI95, 2.3-9.4; P < .001), those of Asian ethnicity (OR, 4.3; CI95, 1.4-13.5; P < .01), and older HCWs (OR, 1.0; CI95, 1.0-1.1; P < .05) were at a higher risk for conversion.

CONCLUSIONS

Although the prevalence of tuberculin positivity decreased after the peak of the recent TB epidemic in New York City, the conversion rate among HCWs in high-risk occupational settings for TB exposure was still greater than that among HCWs in low-risk settings. Continued surveillance of occupational TB infection is needed, especially among high-risk HCWs.

A survey of latent tuberculosis infection among laboratory healthcare workers in New York City

OBJECTIVE

To determine the prevalence of positive tuberculin skin tests (TSTs), incidence of TST conversion, risk factors for positive TSTs, and history of active TB among HCWs in microbiology laboratories in New York City.

DESIGN

Two-year survey from May 1999 to June 2001.

SETTING

Nineteen microbiology laboratories.

RESULTS

During the first year, interviews were conducted with 345 laboratory HCWs (mean, 18 HCWs per site; range, 2 to 51) to assess the prevalence of positive TSTs, but 3 (1%) could not recall their result and were excluded from further analyses. The mean age of the remaining 342 HCWs was 48 years; 68% (n = 233) were female, 54% (n = 183) received bacille Calmette-Guerin (BCG) vaccination, and 71% (n = 244) were foreign born. The prevalence of a positive TST was 57% (n = 196), but only 20% (n = 39) of the HCWs received isoniazid. The incidence of TST conversion in the second year of the study was 1% (1 of 108). Multivariate analysis identified age (odds ratio [OR] per year, 1.05; 95% confidence interval [CI95], 1.02-1.08), foreign birth (OR, 3.80; CI95, 1.98-7.28), BCG immunization (OR, 4.89; CI95, 2.72-8.80), and employment in a mycobacteriology laboratory (OR, 2.14; CI95, 1.25-3.68) as risk factors for a positive TST. Only one HCW had been treated for active TB.

CONCLUSIONS

The prevalence of positive TSTs was high among laboratory HCWs, but the TST conversion rate was low. Higher rates of treatment for latent TB infection are desirable.

Modeling and correction of digit preference in tuberculin surveys

SETTING

Human observers generally have a strong tendency to round analog measurements or estimates to 'nice' ending digits, such as 0, 5, or even numbers. This is known as digit preference; it is a well-known phenomenon in frequency distributions of indurations collected in tuberculin surveys. Digit preference can distort estimates of prevalence and other statistical parameters.

METHODS

We have developed a statistical model that combines smoothing by penalized likelihood and the transfer of counts from non-preferred to preferred digits, to obtain estimates of: 1) the smooth underlying distribution and 2) the amount of digit preference.

RESULTS

To illustrate the validity of the model, it was applied to data from several countries.

CONCLUSION

With the proposed model, digit preference can be quantified and frequency distributions of indurations can be corrected for it.

The prevalence of latent tuberculous infection at nursing homes in the San Juan metropolitan area

We sought to establish the Tuberculin skin status of a representative sample of subjects residing in Nursing Homes in the metropolitan San Juan area. In comparison with similar populations previously described in the medical literature, no difference was found in Tuberculin skin test reactivity in the studied sample.

Yield of casual contact investigation by the hour

OBJECTIVE

Among casual contacts of tuberculosis (TB) patients, to assess how duration of contact, prior mycobacterial exposure, and performance of one or two tuberculin skin tests (TST), affect the likelihood that a positive TST represents conversion.

METHODS

Published estimates of mycobacterial prevalence and BCG coverage, and their effect on single or repeated TSTs, were used to calculate baseline prevalence of TST reactions in four populations commonly encountered in North American contact investigations. Using published estimates of hourly risk of TB infection, the probability that a positive TST represented conversion was calculated.

RESULTS

Among casual contacts with 20 hours of exposure, the likelihood that a single positive TST performed after 8 weeks represented conversion was 77% in persons from populations with low prior mycobacterial exposure, but only 6-8% in foreign-born populations. If tuberculin testing was performed immediately and then again 8 weeks post-exposure, 14-38% of all positive tests would be due to boosting, related to prior exposure to mycobacteria or BCG. If one TST, performed 8 weeks after exposure, was positive in casual contacts from populations with high prevalence of prior mycobacterial exposures, the likelihood of true conversion was less than 40%, even after 200 hours of exposure.

CONCLUSIONS

A single TST performed 8 weeks after the end of exposure among casual contacts will detect all true conversions, and minimize misdiagnosis due to boosting. The decision to perform TST on casual contacts should consider the likelihood of prior mycobacterial exposure in the population, as well as the duration of exposure.

Analysis of the frequency distribution of tuberculin skin test readings: a tool for the assessment of group contact investigations

SETTING

The public health tuberculosis control program covering Seattle, Washington, and its surrounding suburban areas.

OBJECTIVE

To describe a tool of potential usefulness in the assessment of transmission of tuberculosis in contact investigations of groups, such as co-workers or schoolmates of an infectious case, with a low prior probability of latent tuberculosis infection (LTBI).

DESIGN

Tuberculin skin test (TST) readings in mm of the group being tested were graphed and compared with the known frequency distributions of TST readings of populations with and without LTBI, the latter including a fraction with non-specific tuberculin reactivity.

RESULTS

Four group contact investigations were analyzed retrospectively with this tool. In two the graphed TST readings of contacts fell within the distribution of a population with LTBI, and suggested that transmission had occurred. In the other two, the graphed readings better fit the distribution of a population with non-specific tuberculin reactivity and suggested that transmission had not occurred.

CONCLUSION

This simple tool to facilitate the determination of whether transmission of tuberculosis has occurred, and who should be offered treatment for LTBI in contact investigations of groups of people, deserves further study.

Assessment of tuberculosis screening and management practices of large jail systems

OBJECTIVE

This descriptive study sought to explore the use and timeliness of tuberculosis (TB) screening and management activities in jail facilities.

METHODS

Study personnel visited 20 large U.S. jail systems and reviewed the medical records of 56 inmates who had recently been evaluated for TB disease and 376 inmates who were diagnosed with or confirmed to have latent TB infection (LTBI). Data from these records were analyzed to determine completion and timeliness of screening, diagnostic, and treatment activities.

RESULTS

In 14% of 56 inmates evaluated for TB disease and 24% of 376 inmates with LTBI, chest radiographs were either not performed or not documented. Of 48 inmates evaluated for TB disease who were not receiving treatment when admitted to jail, 10 had no record of sputum collection being done. A mean delay of 3.1 days occurred from symptom report to respiratory isolation. Time from tuberculin skin test reading to chest radiograph reading was a mean of 5.3 days in inmates evaluated for TB disease and a mean of 7.0 days in inmates with LTBI. Follow-up was arranged for 91% of released inmates who were on treatment for TB disease and only 17% of released inmates who were on treatment for LTBI.

CONCLUSIONS

Jail health information systems should be augmented to better document and monitor inmate health care related to TB. Completion rates and timeliness of TB screening, diagnostic, and treatment measures should be evaluated to identify areas needing improvement. Finally, mechanisms for continuity of care upon inmate release should be enhanced to promote therapy completion and prevent TB transmission in the community.

[First time tuberculin skin test among children in Asaminami-ward, Hiroshima City]

Tuberculin skin test (TST) was performed on 7,398 babies and infants from April 2000 to September 2002 in Asaminami Public Health Center, Hiroshima City. Positive (diameter of erythema > or = 10 mm) rate first time TST among children above six months was higher than that of babies below six months. Second time TST among children above six months hardly became negative. Six children were indicated chemoprophylaxis by the results of second time TST and detailed examination, however, all 6 children did not meet with clinical criterion of chemoprophylaxis, and further studies are needed whether such weak positive reaction is specific for tuberculosis infection or not.

A prospective study of bacillus Calmette-Guérin scar formation and tuberculin skin test reactivity in infants in Lima, Peru

OBJECTIVES

To determine the sensitivity of the bacillus Calmette-Guérin (BCG) scar as an indicator of previous vaccination and to ascertain the tuberculin skin test (TST) response in infancy after vaccination in a community from an area hyperendemic for tuberculosis (TB).

METHODS

In a birth cohort of healthy term infants from Lima, Peru, a single dose of BCG vaccine was administered within the first month of life. Scar formation was assessed biweekly during the first 6 months and again at 3 years after vaccination. TST response was evaluated 6 months after vaccination.

RESULTS

Six months after vaccination, 99% (68) of the newborns exhibited a BCG scar (>2 mm). Scar size did not differ by sex, birth weight, age at vaccination, or nutritional status in the first 2 months. Eighty percent of the participants were found 3 years after vaccination, and all of them had a BCG scar. Mean TST reaction size 6 months after vaccination was 2.9 +/- 0.3 mm. No association was found between sex or age at BCG vaccination and TST size. Only 3 children had a TST >10 mm, and the 3 had a TB contact at home.

CONCLUSIONS

The BCG scar was a sensitive indicator of vaccination status up to 3 years after the administration of the vaccine in the first month of life. Although nearly a quarter of the children had a TST response >5 mm 6 months after vaccination, TST reactions >10 mm did not occur in the absence of exposure to a person with tuberculosis. A cutoff of 10 mm should be used for disease control purposes in people who are born in countries where TB is endemic.

Annual risk of tuberculous infection in Khammam a tribal district of Andhra Pradesh

A tuberculin survey to estimate annual risk of tuberculosis was conducted in Khammam tribal district during 2001-2002. A total of 8637 children were test-read--2991 without BCG scar and 5442 with BCG scar. The tests were performed using ITU PPD RT23 and the maximum size of induration was recorded at about 72 hours after the test. Based on the frequency distribution of reaction size, cut-off point for infection with tubercle bacilli was considered at 12 mm. Using this criterion, the prevalence of infection was estimated at 11.8% among children without BCG scar and 10.6% among children with BCG scar. This difference was found to be statistically insignificant. ARTI rates computed from the prevalence estimates among children without and with BCG scar were 1.6% and 1.5% respectively. It was computed as 1.5% from the prevalence in the combined group i.e. irrespective of BCG scar status.

Impact of monetary incentives on adherence to referral for screening chest x-rays after syringe exchange-based tuberculin skin testing

INTRODUCTION

Syringe-exchange programs (SEPs) have proven to be valuable sites to conduct tuberculin skin testing among active injection drug users. Chest x-rays (CXRs) are needed to exclude active tuberculosis prior to initiating treatment for latent tuberculosis infection. Adherence of drug users to referral for off-site chest x-rays has been incomplete. Previous cost modeling demonstrated that a monetary incentive to promote adherence could be justified on the cost basis if it had even a modest effect on adherence.

METHODS

We compared adherence to referral for chest x-rays among injection drug users undergoing syringe exchange-based tuberculosis screening in New York City before and after the implementation of monetary incentives.

RESULTS

From 1995 to 1998, there were 119 IDUs referred for CXRs based on tuberculin skin testing at the SEP. From 1999 to 2001, there were 58 IDUs referred for CXRs with a $25 incentive based on adherence. Adherence to CXR referral within 7 days was 46/58 (79%) among individuals who received the monetary incentive versus 17/119 (14%) prior to the implementation of the monetary incentive (P<.0001; odds ratio [OR]=23; 95% confidence interval [CI]=9.5-57). The median time to obtaining a CXR was significantly shorter among those given the incentive than among those referred without the incentive (2 vs. 11 days, P<.0001). In multivariate logistic regression analysis, use of the incentive was highly independently associated with increased adherence (OR=22.9; 95% CI=10-52).

CONCLUSIONS

Monetary incentives are highly effective in increasing adherence to referral for screening CXRs to exclude active tuberculosis after syringe exchange-based tuberculin skin testing. Prior cost modeling demonstrated that monetary incentives could be justified on the cost basis if they had even a modest effect on adherence. The current data demonstrated that monetary incentives are highly effective at increasing adherence in this setting and therefore are justifiable on a cost basis. When health care interventions for drug users require referral off site, monetary incentives may be particularly valuable in promoting adherence.

Annual risk of tuberculous infection in the western zone of India

SETTING

Rural and urban areas of six selected districts in the western zone of India.

OBJECTIVES

To estimate the annual risk of tuberculous infection (ARI).

DESIGN

A community-based, cross-sectional tuberculin survey was conducted among children aged 1-9 years residing in a sample of rural and urban areas of six districts in the western zone of India. Stratified two-stage cluster sampling was adopted for selection of rural and urban clusters. A total of 48473 children in 600 clusters underwent tuberculin testing with 1TU PPD RT23 with Tween 80; the induration was measured about 72 h after the test.

RESULTS

The BCG scar was observed in 52% of the test-read children. Estimation of the prevalence of infection was based on the frequency distribution of tuberculin reaction size among 22259 children without BCG scar. Reactions > or = 15 mm were considered attributable to infection with tubercle bacilli. The prevalence of infection was estimated to be 9.3%, and the ARI computed from the estimated prevalence was 1.8%. The proportion of infected children was found to be significantly higher in urban than in rural areas.

CONCLUSION

The high rate of ARI in the western zone of India calls for further intensification of tuberculosis control efforts.

Annual risk of tuberculous infection in rural areas of Uttar Pradesh, India

SETTING

Rural areas in Uttar Pradesh, the most populous state in India.

OBJECTIVES

1) To estimate the average annual risk of tuberculous infection (ARI), 2) to study ARI trends with age, and 3) to compare tuberculin reactions among children with and without BCG scar.

STUDY DESIGN

A cross-sectional tuberculin survey was conducted among children aged 1-9 years residing in Rae Bareli, Hardoi and Jaunpur districts, Uttar Pradesh. Tuberculin testing was performed using 1TU of PPD RT23 with Tween 80, and indurations were measured 72 hours later. Prevalence of infection was estimated in children without BCG scar based on the cut-off point identified on the frequency distribution of reaction sizes. The ARI was computed from the estimated prevalence.

RESULTS

The proportion of children with BCG scar varied from 25% to 31% in the study districts. Using a cut-off of 14 mm among children without BCG scar, the ARI was estimated at 2.3% in Rae Bareli, 1.9% in Hardoi and 1.5% in Jaunpur, and was observed to increase with age. Tuberculin test results among children with BCG scar suggest that they may be included in tuberculin surveys to estimate ARI.

CONCLUSION

High rates of transmission of tuberculous infection suggest that tuberculosis control measures need to be intensified.

Risk factors for tuberculosis infection in children in contact with infectious tuberculosis cases in the Gambia, West Africa

OBJECTIVE

Tuberculosis (TB) infection is highly prevalent in developing countries. As infected children represent a large proportion of the pool from which TB cases will arise, knowledge of the factors that influence TB infection in children are of importance to evaluate transmission of infection in the community and adapt TB control activities. There are limited data on the risk of infection in child populations in developing countries.

METHODS

We performed a household contact study in The Gambia (West Africa), in which children who were living in contact with individuals who had proven smear-positive pulmonary TB cases were investigated. A questionnaire was addressed to the mother or caregiver of the child to investigate the presence of various risk factors and assess the degree of exposure of the child to the individual with TB within the household. A tuberculin skin test (TST) was performed on each child. TST sizes > or =5 and 10 mm, respectively, were considered positive.

RESULTS

Households of 206 TB cases were visited, and 384 children aged <5 years were examined. The median age was 2, and 48% were girls. The distribution of TST responses followed a bimodal pattern, with 135 (35%) children presenting a palpable induration. Random effects logistic regression analysis demonstrated that the risk of positive TST response in the child increased with the geographic proximity of the child to the individual with TB within the household and with the degree of activities shared with the individual with TB. It was also associated with the clinical severity of the disease in the index case. Nutritional status and presence of a bacille Calmette-Guérin (BCG) scar were not independent risk factors for TST positivity in this population. On multivariate analysis, the effect of geographic proximity to the individual with TB, household size, and duration of cough in the index case persisted for TST responses > or =5 mm.

CONCLUSIONS

In a highly endemic country with high BCG vaccination coverage in Africa, TB infection in children who were in contact with individual with infectious TB was directly related to the intensity of exposure of the child to the individual with TB. Our data suggest that a positive TST in a child reflects most probably TB infection rather than previous BCG vaccination. Contact tracing can play a major role in the control of TB in developing countries.

Specific delayed-type hypersensitivity responses to ESAT-6 identify tuberculosis-infected cattle

Human and bovine tuberculosis have long been detected by skin testing with purified protein derivative (PPD), a complex mix of partly denatured mycobacterial antigens with suboptimal specificity. In the present study, skin tests based on ESAT-6, a recombinantly produced antigen highly specific for tuberculosis infection, were investigated. Although ESAT-6 was strongly recognized in vitro and induced high levels of gamma interferon, initial investigations demonstrated that higher doses of ESAT-6 than of PPD were needed to induce substantial delayed-type hypersensitivity reactions. Also, the kinetics of the skin test response differed for the two reagents; PPD showed maximal response at 72 h, but the response to ESAT-6 often peaked later at 96 h. Tests based on an optimized strategy (400 micro g of ESAT-6 measured between 72 and 96 h), in cattle infected with Mycobacterium bovis (n = 22) and animals sensitized by exposure to environmental mycobacteria showed ESAT-6 to have a promising diagnostic potential (sensitivity, 82%; specificity, 100%; optimal cutoff, 3 mm), compared with PPD (sensitivity, 86%; specificity, 90%; optimal cutoff, 4 mm). Larger investigations are required to refine cutoff points for any new diagnostic test, but the present results indicate great potential for skin tests based on specific antigens for accurate in vivo diagnosis of tuberculosis.

Results of an extended tuberculosis screening programme among sixth formers in a London school--more questions than answers

Following the death of an unvaccinated 16-year-old school student with isoniazid resistant pulmonary tuberculosis, extended screening of sixth formers took place to identify further cases of tuberculosis and to establish the need for BCG vaccination. Eight hundred and four 16-19 year olds in the school underwent Heaf testing and completed a demographics questionnaire. Forty-nine (5.5%) of these children had a positive Heaf test and were offered a chest radiograph. Four children were diagnosed with pulmonary or mediastinal tuberculosis, none linked to the index case. Fifty-four students (6.7%) with no prior BCG had a Heaf grade 0-1 reaction and were recommended for vaccination. Ninety-one percent of students were from ethnic minority groups and 29% had been born outside the UK. British Thoracic Society recommendations on the management of tuberculin positive cases of this is open to interpretation and we suggest that a more directed and aggressive approach to TB control should be considered in inner city schools with a high proportion of at risk ethnic minority students.

Tuberculin testing and risk of tuberculosis infection among New York City schoolchildren

OBJECTIVES

To assess adherence to a 1996 health policy change, which discontinued mandatory tuberculin skin testing (TST) of new entrants to NYC primary schools and continued mandatory testing of new entrants to secondary schools.

METHODS

The proportion tested before (1991-1995) and after (1996-1998) the change in health policy was determined. Factors associated with TST positivity and the cost of continued testing were assessed.

RESULTS

A total of 76.6% of 551 636 new entrants to primary schools were tested in 1991-1995; slightly fewer, 71.1% of 339 958, were tested in 1996- 1998. Among new entrants to secondary schools, 31.0% of 106 463 were tested in 1991-1995 and 51.4% of 53 762 were tested in 1996-1998. The proportion who were TST-positive continued to decrease after 1996 to 1.2% among primary and 9.7% among secondary schoolchildren in 1998. Older age and birth outside the United States were associated with TST positivity. The estimated minimum cost of continued testing in primary schools was $123 152 per tuberculosis case prevented.

CONCLUSION

An approach aimed at reducing testing of children at low risk for latent tuberculosis infection did not decrease testing of younger children. More important, older children who were more likely to be born in countries of high tuberculosis incidence were not tested. Additional efforts are needed to increase awareness among medical and school personnel to decrease testing among children who do not have risk factors for latent tuberculosis infection and to increase tuberculin testing of children who are entering school for the first time at the secondary level and do have risk factors for tuberculosis infection.