Skin Test Conversion Research Articles

An outbreak involving extensive transmission of a virulent strain of Mycobacterium tuberculosis.

From 1994 to 1996, there was a large outbreak of tuberculosis in a small, rural community with a population at low risk for tuberculosis. Twenty-one patients with tuberculosis (15 with positive cultures) were identified; the DNA fingerprints of the 13 isolates available for testing were identical. To determine the extent of transmission, we investigated both the close and casual contacts of the patients. Using a mouse model, we also studied the virulence of the strain of Mycobacterium tuberculosis that caused the outbreak. The index patient, in whom tuberculosis was diagnosed in 1995; the source patient, in whom the disease was diagnosed in 1994; and a patient in whom the disease was diagnosed in 1996 infected the other 18 persons. In five, active disease developed after only brief, casual exposure. There was extensive transmission from the three patients to both close and casual contacts. Of the 429 contacts, 311 (72 percent) had positive skin tests, including 81 [corrected] with documented skin-test conversions. Mice infected with the virulent Erdman strain of M. tuberculosis had approximately 1000 bacilli per lung after 10 days and about 10,000 bacilli per lung after 20 days. In contrast, mice infected with the strain involved in the outbreak had about 10,000 bacilli per lung after 10 days and about 10 million bacilli per lung after 20 days. In this outbreak of tuberculosis, the growth characteristics of the strain involved greatly exceeded those of other clinical isolates of M. tuberculosis. The extensive transmission of tuberculosis may have been due to the increased virulence of the strain rather than to environmental factors or patient characteristics.

Actions taken by nursing education programs in the United States to prevent tuberculosis transmission in nursing students.

Measures to prevent tuberculosis include education and skin testing of at-risk groups, including health care workers. This study focused on policies and practices related to tuberculosis in nursing education programs, especially skin testing and instruction. Data were collected from a stratified random sample of nursing administrators in associate and baccalaureate degree programs in the United States using an instrument adapted from a medical school study. Several factors may have contributed to fewer skin test conversions in nursing programs than in medical schools. Although most nursing education programs considered skin testing a priority, there were inconsistencies related to skin testing type and process when compared with recent Centers for Disease Control and Prevention guidelines. Major content gaps related to multidrug-resistant tuberculosis and the differences between pulmonary and extrapulmonary symptomatology were found.

Low risk for tuberculosis in a regional pediatric hospital: nine-year study of community rates and the mandatory employee tuberculin skin-test program.

To assess the risk of Mycobacterium tuberculosis infection and disease among patients and workers in a regional pediatric hospital. Descriptive epidemiological study of the mandatory tuberculin skin testing program of hospital employees at hire and during annual reevaluation, pediatric patients with tuberculosis (TB), efficacy of hospital infection control measures, and community rates of TB. 361-bed, university, pediatric hospital serving Cincinnati (1.7 million population). During 1986 through 1994, 2,275 to 4,356 employees were compliant with Mantoux skin testing and screening each year. This represented >97% of the population who were eligible for screening. The cumulative rate of M tuberculosis infection from a previous positive tuberculin skin test was 10% to 12% per year during 1986 through 1994. Among new Mantoux skin-test converters in employees at annual reevaluation, the risk of TB infection was 0.3% in 1993 and 1994. There were no active cases of TB identified during new employee screening or annual reevaluation. Of 62 new Mantoux skin-test converters in 9 years, 23% were foreign-born, 13% were Asian, 23% were African American, 11% received the bacillus of Calmette-Guérin vaccine, and 60% had direct patient care or indirect patient contact. A cluster of five converters occurred in a department with no patient care or contact. Mantoux conversion rates were 1.9 per 1,000 employee patient-care or contact-years and 2.2 per 1,000 employee non-patient-contact years. Twenty pediatric patients with active TB were identified during 1991 to 1994, with < or =6 cases per year, placing this hospital in the low-risk category for M tuberculosis disease. Three children with pulmonary TB were admitted without immediate respiratory isolation, possibly exposing 9 patients and 42 employees; none converted their Mantoux skin tests on retesting. Rates of active TB in Cincinnati were stable during the period (eg, 8/100,000 population in 1994). Despite intense active surveillance among thousands of hospital employees with >97% annual compliance, tuberculin conversion rates were low, and no cases of active TB were identified during 9 years of follow-up. There was no evidence of transmission of M tuberculosis from infected patients to employees during uncontrolled exposures. Rates of TB in the community were low. These data suggest that rigorous application of the Centers for Disease Control and Prevention guidelines and Occupation Safety and Health Administration regulations for preventing nosocomial TB in pediatric hospitals may be excessive and costly. Special provisions should be made for pediatric hospitals with a proven low risk of transmission of M tuberculosis.

Low Risk for Tuberculosis in a Regional Pediatric Hospital: Nine-Year Study of Community Rates and the Mandatory Employee Tuberculin Skin-Test Program

To assess the risk of Mycobacterium tuberculosis infection and disease among patients and workers in a regional pediatric hospital.Descriptive epidemiological study of the mandatory tuberculin skin testing program of hospital employees at hire and during annual reevaluation, pediatric patients with tuberculosis (TB), efficacy of hospital infection control measures, and community rates of TB.361-bed, university, pediatric hospital serving Cincinnati (1.7 million population).During 1986 through 1994, 2,275 to 4,356 employees were compliant with Mantoux skin testing and screening each year. This represented >97% of the population who were eligible for screening. The cumulative rate of M tuberculosis infection from a previous positive tuberculin skin test was 10% to 12% per year during 1986 through 1994. Among new Mantoux skin-test converters in employees at annual reevaluation, the risk of TB infection was 0.3% in 1993 and 1994. There were no active cases of TB identified during new employee screening or annual reevaluation. Of 62 new Mantoux skin-test converters in 9 years, 23% were foreign-born, 13% were Asian, 23% were African American, 11% received the bacillus of Calmette-Guérin vaccine, and 60% had direct patient care or indirect patient contact. A cluster of five converters occurred in a department with no patient care or contact. Mantoux conversion rates were 1.9 per 1,000 employee patient-care or contact-years and 2.2 per 1,000 employee non-patient-contact years. Twenty pediatric patients with active TB were identified during 1991 to 1994, with < or =6 cases per year, placing this hospital in the low-risk category for M tuberculosis disease. Three children with pulmonary TB were admitted without immediate respiratory isolation, possibly exposing 9 patients and 42 employees; none converted their Mantoux skin tests on retesting. Rates of active TB in Cincinnati were stable during the period (eg, 8/100,000 population in 1994).Despite intense active surveillance among thousands of hospital employees with >97% annual compliance, tuberculin conversion rates were low, and no cases of active TB were identified during 9 years of follow-up. There was no evidence of transmission of M tuberculosis from infected patients to employees during uncontrolled exposures. Rates of TB in the community were low. These data suggest that rigorous application of the Centers for Disease Control and Prevention guidelines and Occupation Safety and Health Administration regulations for preventing nosocomial TB in pediatric hospitals may be excessive and costly. Special provisions should be made for pediatric hospitals with a proven low risk of transmission of M tuberculosis.

Incidence of latex sensitization among latex glove users

Background: Although there are several reports of the prevalence of latex sensitization among health care workers, the incidence of sensitization is unknown. Objective: The objective of this study was to estimate the incidence of sensitization among latex glove users at a hospital in Hamilton, Ontario, Canada. Methods: Workers with negative results to the skin test at baseline were followed prospectively over 1 year, some wearing powdered gloves and others using powder-free gloves. They were reevaluated in 1995 with a questionnaire and skin prick test (SPT) sensitivity to latex reagents, three common inhalants, and six foods. A conversion was defined as a (new) latex SPT with wheal diameter at least 4 mm greater than saline control. Glove extracts were assayed for antigenic protein, and air samples were obtained to estimate exposure to airborne latex protein. Results: During powdered glove use, personal exposures ranged from 5 to 616 ng/m 3, whereas during powder-free glove use, all but two results for air samples were below the limit of detection (about 0.1 ng/m 3). During the study period, the protein concentration in the powdered gloves, initially mean 557 μg/gm of sample, declined at a rate of 295 μg/gm per year ( p < 0.0001). Of the 1075 SPT-negative participants at baseline, 479 were working in eligible wards, and of these, 435 (91%) participated in follow-up, 227 using powder-free gloves and 208 using powdered gloves. We identified four conversions, two (1.0%) in the powdered glove group and two (0.9%) in the powder-free group. The two participants using powdered gloves were the only converters who were symptomatic. The significance of skin test conversions identified in the powder-free group, both asymptomatic patients, is unclear. The limitations of the study are discussed, including the limited power, the declines in latex protein concentrations, and the possibility of information (observer) bias. Conclusion: To our knowledge, this represents the first reported estimate (about 1%) of incidence of sensitization in hospital personnel using latex gloves. (J Allergy Clin Immunol 1998;101:171-8.)

Incidence of tuberculosis infection among New York State prison employees.

This study examined tuberculosis skin test conversions among 24,487 New York State prison employees in 1992. Conversions were analyzed by prison and by job category. The conversion rate was 1.9%. Employees in prisons with low and high numbers of prisoner cases had odds ratios for conversion of 1.67 (95% confidence interval [CI] = 1.27, 2.19) and 2.20 (95% CI = 1.69, 2.87), respectively, relative to employees in prisons with no prisoner cases. In prisons with cases, guards and medical personnel had odds ratios of 1.64 (95% CI = 1.11, 2.43) and 2.39 (95% CI = 1.40, 4.08), respectively, relative to employees with little prisoner contact. In 1992, approximately one third of new infections among New York State prison employees were due to occupational exposure.

Outbreak of drug-resistant tuberculosis with second-generation transmission in a high school in California

Background: In spring 1993, four students in a high school were diagnosed with tuberculosis resistant to isoniazid, streptomycin, and ethionamide. Methods: To investigate potential transmission of drug-resistant tuberculosis, a retrospective cohort study with case investigation and screening by tuberculin skin tests and symptom checks was conducted in a high school of approximately 1400 students. Current and graduated high-school students were included in the investigation. DNA fingerprinting of available isolates was performed. Results: Eighteen students with active tuberculosis were identified, Through epidemiologic and laboratory investigation, 13 cases were linked; 8 entered 12th grade in fall 1993; 9 of 13 had positive cultures for Mycobacterium tuberculosis with isoniazid, streptomycin, and ethionamide resistance, and all 8 available isolates had identical DNA fingerprints. No staff member had tuberculosis. One student remained infectious for 29 months, from January 1991 to June 1993, and was the source case for the outbreak. Another student was infectious for 5 months before diagnosis in May 1993 and was a treatment failure in February 1994 with development of rifampin and ethambutol resistance in addition to isoniazid, streptomycin, and ethionamide. In the fall 1993 screening, 292 of 1263 (23%) students tested had a positive tuberculin skin test. Risk of infection was highest among 12th graders and classroom contacts of the two students with prolonged infectiousness. An additional 94 of 928 (10%) students tested in spring 1994 had a positive tuberculin skin test; 22 were classroom contacts of the student with treatment failure and 21 of these had documented tuberculin skin test conversions. Conclusion: Extensive transmission of drug-resistant tuberculosis was documented in this high school, along with missed opportunities for prevention and control of this outbreak. Prompt identification of tuberculosis cases and timely interventions should help reduce this public health problem. (J Pediatr 1997;131:863-8)

TB Skin-Test Conversion Rates Among Exposed Hospital Workers

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Occupational risk ofMycobacterium tuberculosis infection in hospital workers

We conducted a 4-year (1/89-12/92) retrospective cohort study among employees at a large metropolitan hospital where a nosocomial outbreak of multidrug-resistant tuberculosis (TB) had occurred. We compared the risk of tuberculin skin test (TST) conversion among employees who worked on wards where patients with culture-confirmed TB were cared for ("exposed") with the risk among employees who worked on wards with no such patients ("unexposed"). Exposed employees had a higher 4-year risk of TST conversion (14.5%) than unexposed employees (1.4%) (adjusted relative risk 13.4; 95 percent confidence interval 5.1-35.2). Exposed employees had significantly higher risks of conversion than unexposed employees during 1989-91, but not for 1992. Among the exposed, ward clerks had a risk of conversion (15.6%) only slightly lower than nurses (18.2%). We conclude that employees who worked in areas where patients with active M. tuberculosis infection were cared for, including workers who did not provide direct patient care, had a higher risk of TST conversion than employees who did not work in these areas. Reasons for the decline in risk over time include outbreak termination, fewer admissions of patients with TB, implementation of effective infection control measures, and possible resistance to infection in some members of the study population.

Transmission of a Highly Drug-Resistant Strain (Strain W1) of Mycobacterium tuberculosis

Nosocomial transmission of multidrug-resistant tuberculosis (MDR TB) has been reported primarily in New York State and has generally been presumed to occur via respiratory aerosols. To assess nosocomial transmission of MDR TB. In 1995, 8 patients with MDR TB were identified in South Carolina; all were resistant to 7 drugs and had matching DNA fingerprints (strain W1). Community linkswere identified for 5 patients (Patients 1-5). However, no links were identified forthe other 3 patients (Patients 6-8) except being hospitalized at the same hospital as 1 community patient. Outbreak investigation. Community and hospital. Eight patients whose MDR TB isolates had DNA fingerprint patterns matching strain W1. Clinical characteristics of patients with strain W1 Mycobacterium tuberculosis isolates. Patient 5 (community patient) and Patient 8, diagnosed April 1995 and November 1995, respectively, had clinical courses consistent with MDR TB, with smear-positive and culture-positive specimens and cavitary lesions on chest radiograph; both died of MDR TB less than 1 month after diagnosis. Patients 6 and 7 (diagnosed May 1995) each had 1 positive culture for MDR TB; specimens were collected during bronchoscopy. Patient 6 had a skin test conversion after bronchoscopy. Neither Patient 6 nor Patient 7 had a clinical course consistent with MDR TB, neither was treated for MDR TB, and both are alive and well. No evidence of laboratory contamination of specimens, transmission on inpatient wards, or contact among patients was found. All 4 received bronchoscopies in May 1995; Patients 6, 7, and 8 had bronchoscopies 1, 12, and 17 days, respectively, after Patient 5. Observations revealed that bronchoscope cleaning was inadequate, and the bronchoscope was never immersed in disinfectant. Inadequate cleaning and disinfection of the bronchoscope after the procedure performed on Patient 5 led to subsequent false-positive cultures in Patients 6 and 7 and transmission of infection to Patient 6 and active MDR TB to Patient 8.

Tuberculosis in health care settings and the estimated benefits of engineering controls and respiratory protection.

Intra-institutional spread of tuberculosis (Tb) has re-emerged as a substantial public and occupational health threat. To characterize the person-hours and lifetime risks of Tb-related morbidity and mortality, we performed a risk assessment for health care workers (HCWs) developing Tb-related morbidity and mortality at varying levels of exposure, engineering controls, and respiratory protection. Under average conditions of exposure, one Tb skin-test conversion is estimated to occur for every 2650 person-hours of work by unprotected workers. With higher exposures, a skin-test conversion for an unprotected worker may occur in as few as 3 person-hours. Use of respiratory protection is estimated to reduce risks by the following proportions: surgical mask, 2.4-fold; disposable dust, fume, mist, or disposable high-efficiency particulate air filtering (HEPA) mask, 17.5-fold; elastomeric HEPA cartridge respirator, 45.5-fold; or powered air-purifying respirator (PAPR), 238-fold. Assuming a lifetime exposure of 250 hours, the risk of a skin-test conversion is estimated to be 9%. We conclude that HCWs are at substantial risk for Tb-related morbidity and mortality, and that administrative controls, engineering controls, and respirators offer substantial benefits in risk reduction.

Reduction in Tuberculin Skin-Test Conversions among Medical House Staff Associated with Improved Tuberculosis Infection Control Practices

To assess the efficacy of an infection control program as measured by tuberculin skin-test (TST) conversion rates in medical house staff.Observational study.University-based hospital in New York City serving a large indigent population.Medical house staff.TST conversions were measured every 6 months in medical house staff from June 1992 to June 1994. Compliance with the isolation policy was measured by identifying room locations 24 hours after admission of patients who had Mycobacterium tuberculosis recovered from respiratory specimens.The TST conversion rate decreased from 5.8 to 0, 2.3, and 0 per 100 person years of exposure in successive 6-month periods. The estimated annual TST conversion rate among interns fell from 7 per 100 person years in June 1992 to 0 per 100 person years in June 1993 and 0 per 100 person years in June 1994 (P < .029). The proportion of patients with pulmonary tuberculosis who were isolated in negative-pressure rooms increased from 38% to 75% over the study period (P < .01).Development of a multifaceted infection control program can decrease the risk of nosocomial tuberculosis infection in medical house staff.

Varied approaches to tuberculosis control in a multihospital system.

To document the actual tuberculosis (TB) control policies and procedures in a nonoutbreak setting in a variety of hospitals. To determine if any particular practices are linked to higher rates of employee tuberculin skin-test conversion. Survey of hospital occupational health and infection control practitioners for the year 1994 regarding hospital TB policies. Review of hospital records to verify the number of patients with TB at each hospital and to verify the number of employees with positive tuberculin skin tests. Smoke-stick testing of negative-pressure ventilation rooms. A 13-hospital health system in the Midwest. Hospitals ranged in size from 40 to 1,208 beds (median 220) and employed 150 to 6,500 workers (median 875). There were seven rural and six urban centers, including four teaching hospitals. All 13 hospitals had TB control plans, and all performed annual tuberculin skin testing on employees. Annual skin-test positivity rates ranged from 0% to 1.0% (median 0.3%). Negative-pressure ventilation rooms were available in 11 hospitals. The percentage of negative-pressure rooms with effective negative pressure ranged from 44% to 100% (median 95%). Three of the 13 hospitals used high-efficiency particulate air (HEPA) masks as primary personal respiratory protection, and 8 used dust-mist or dust-mist-fume masks. We found no relation between the type of face mask used, number of functional negative-pressure rooms, or hospital TB risk category, and employee skin-test conversion rates. Considerable variation existed in the TB control policies and procedures between hospitals, but employee TB skin-test conversion rates were low in all settings.

Reduction in tuberculin skin-test conversions among medical house staff associated with improved tuberculosis infection control practices.

To assess the efficacy of an infection control program as measured by tuberculin skin-test (TST) conversion rates in medical house staff. Observational study. University-based hospital in New York City serving a large indigent population. Medical house staff. TST conversions were measured every 6 months in medical house staff from June 1992 to June 1994. Compliance with the isolation policy was measured by identifying room locations 24 hours after admission of patients who had Mycobacterium tuberculosis recovered from respiratory specimens. The TST conversion rate decreased from 5.8 to 0, 2.3, and 0 per 100 person years of exposure in successive 6-month periods. The estimated annual TST conversion rate among interns fell from 7 per 100 person years in June 1992 to 0 per 100 person years in June 1993 and 0 per 100 person years in June 1994 (P < .029). The proportion of patients with pulmonary tuberculosis who were isolated in negative-pressure rooms increased from 38% to 75% over the study period (P < .01). Development of a multifaceted infection control program can decrease the risk of nosocomial tuberculosis infection in medical house staff.

A pseudo-outbreak of purified protein derivative skin-test conversions caused by inappropriate testing materials.

To investigate a cluster of newly identified tuberculosis infections. A field study was conducted including interviews; medical record reviews; checking of bills and invoices, pharmacy records, and drug manufacturer information; and clinical retesting. Community residential facilities providing comprehensive services to retarded adults. Twenty residential facility staff (not previously known to be purified protein derivative [PPD] positive). Staff had been tested with 250 TU of PPD, and 9 of 20 were tuberculin positive. Retesting with 5 TU yielded no reaction. Reactions were attributable to testing with a product not recommended for routine PPD screening. Healthcare workers planting PPD Mantoux tests always should check the vials to ensure that the appropriate strength solution is being used.

Reduction in tuberculin skin-test conversion rate after improved adherence to tuberculosis isolation.

The rate of purified protein derivative (PPD) conversion in workers at our hospital increased to 1.7% in 1991. After implementation of mandatory respiratory isolation of patients with community-acquired pneumonia, the rate dropped to 0.6%. This policy may protect workers in institutions where the majority of patients with pneumonia have risk factors for tuberculosis.

Reduction in Tuberculin Skin-Test Conversion Rate after Improved Adherence to Tuberculosis Isolation

The rate of purified protein derivative (PPD) conversion in workers at our hospital increased to 1.7% in 1991. After implementation of mandatory respiratory isolation of patients with community-acquired pneumonia, the rate dropped to 0.6%. This policy may protect workers in institutions where the majority of patients with pneumonia have risk factors for tuberculosis.

A Pseudo-Outbreak of Purified Protein Derivative Skin-Test Conversions Caused by Inappropriate Testing Materials

A Pseudo-Outbreak of Purified Protein Derivative Skin-Test Conversions Caused by Inappropriate Testing Materials

Management After Exposure to Tuberculosis

The increased incidence of tuberculosis—coupled with the emergence of mycobacterial strains resistant to the most effective drugs—has highlighted the importance of identifying transmission and preventing active disease. Skin test conversion can document infection, except in most patients vaccinated with bacille Calmette-Guérin. Prophylactic medication is effective, but not without complications.

Impact of tuberculosis control measures and crowding on the incidence of tuberculous infection in Maryland prisons.

Our aim was to determine the incidence of tuberculin skin test (TST) conversion in the Maryland state correctional system. We conducted a historical longitudinal cohort study. A sample of 1,289 inmates, incarcerated in 16 of 23 prisons, who had a negative TST and a second test within 24 months was selected. The incidence of recent conversion was 6.3 per 100 person-years. Risk factors for conversion included high prison-population density (relative risk [RR] = 2.4; 95% confidence interval [CI], 1.5-3.8) and incarceration in a higher-security institution (RR = 2.4; 95% CI, 1.4-4.3). Incarceration in an institution with higher levels of isoniazid prophylaxis (> 65% of TST positives) reduced the risk of infection by 50% (RR = 0.5; 95% CI, 0.3-0.7). Crowding was strongly correlated with risk of conversion (r = 0.83; P < .001), while rates of isoniazid prophylaxis initiation were inversely correlated with risk of infection (r = -0.82; P < .001). In stepwise regression, higher prison-population density was the strongest predictor of increased infection. In a final model, inclusion of the rate of isoniazid prophylaxis initiation reduced the risk associated with crowding (RR = 1.4; P = .4). Annual screening programs for prisons can identify recent conversions that may not otherwise be detected.