Use of DNA fingerprinting to assess tuberculosis infection control.

BACKGROUND: DNA fingerprinting establishes the genetic relatedness of Mycobacterium tuberculosis isolates and has become a powerful tool in tuberculosis epidemiology. OBJECTIVE: To use DNA fingerprinting to assess the efficacy of current tuberculosis infection-control practices. DESIGN: Retrospective molecular and descriptive epidemiologic study. SETTING: A 700-bed urban public hospital that follows the Centers for Disease Control and Prevention (CDC) guidelines for tuberculosis infection control. PATIENTS: 183 patients who had positive cultures for M. tuberculosis from 1 April 1995 to 31 March 1996. RESULTS: 173 of 183 M. tuberculosis isolates from the study period underwent DNA fingerprinting. Fingerprinting revealed that five isolates represented false-positive cultures and that 91 (54%) of the remaining 168 isolates were in 15 DNA fingerprinting clusters, which ranged in size from 2 to 29 isolates. Risk factors for clustering were birth in the United States, African-American ethnicity, homelessness, substance abuse, and male sex. Retrospective epidemiologic analysis of inpatient and outpatient visits by the 91 patients who had clustered isolates revealed only one possible instance of patient-to-patient transmission. CONCLUSIONS: The DNA fingerprinting of all M. tuberculosis isolates from a 1-year period revealed one possible instance of nosocomial transmission and five false-positive M. tuberculosis cultures. However, these results did not lead to changes in infection-control practices or in clinical care. The study findings do not support the use of DNA fingerprinting for nosocomial tuberculosis surveillance, but they suggest that compliance with the CDC tuberculosis infection-control guidelines may control patient-to-patient transmission in high-risk urban hospitals.

Tuberculosis among Tibetan immigrants from India and Nepal in Minnesota, 1992-1995.

OBJECTIVE: To study screening outcomes among a group of Tibetan immigrants at high risk for developing active tuberculosis (TB) after arrival in Minnesota. DESIGN: Retrospective cohort study. PARTICIPANTS: A total of 191 Tibetan immigrants undergoing medical screening. MAIN OUTCOME MEASURES: Occurrence and treatment outcomes of active TB. SETTING: A health maintenance organization and a public TB clinic in Minneapolis, Minn. RESULTS: Positive (induration, > or =10 mm) tuberculin skin test results were documented in 98% of Tibetans, compared with 44% of Vietnamese, 10% of Hmong, and 51% of Russian refugees in Minnesota (P<.001 for each group). Sixteen active cases (8.4%) were confirmed by isolation of Mycobacterium tuberculosis; however, 5 (31%) were culture-negative on initial screening in Minnesota. Seven cases (44%) were diagnosed during initial screening efforts, and 9 cases (56%) were diagnosed a mean of 19 months (range, 10-27 months) after their initial medical evaluation. Of these 9 cases, 6 (38% of all Tibetan cases) had isolates resistant to 1 or more antituberculous drugs, and 3 (19% of all Tibetan cases) were multidrug resistant (MDR TB). All 3 MDR TB cases were culture-negative on initial screening; these cases constituted 75% of the MDR TB isolates in Minnesota in 1994. The presence of MDR TB was associated with a known history of active TB in Asia (P<.02). Any abnormality on chest radiograph noted either during the Immigration and Naturalization Service screening evaluation in India (relative risk [RR], 5.2; P=.006) or on arrival in Minnesota (RR, 6.8; P=.005) was associated with an increased risk of subsequent active TB. CONCLUSIONS: Tuberculosis infection is nearly universal among Tibetans settling in Minnesota. A single screening evaluation failed to detect the majority of TB cases among Tibetans. Even in the face of negative M tuberculosis cultures, persons with a history of active TB require particularly close follow-up.

Suppressive effect of antioxidants on intercellular adhesion molecule-1 (ICAM-1) expression in human epidermal keratinocytes.

Intercellular adhesion molecule-1 (ICAM-1) is strongly expressed by human epidermal keratinocytes during the course of inflammatory skin diseases. To test the possibility that reactive oxygen species produced in the skin during an inflammatory response affect ICAM-1 expression, cultured human epidermal keratinocytes were treated with H2O2 at concentrations that did not damage the cells, and cell-surface ICAM-1 expression was analyzed. Expression of ICAM-1 was induced on keratinocytes by treatment with 300 microM H2O2 for 1 h. The antioxidant N-acetyl-L-cysteine strongly inhibited H2O2-induced ICAM-1 expression, whereas the antioxidants pyrrolidine dithiocarbamate and alpha-tocopherol were less inhibitory. N-acetyl-L-cysteine also suppressed keratinocyte surface expression of ICAM-1 induced by the cytokines interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha), whereas pyrrolidine dithiocarbamate and alpha-tocopherol suppressed IFN-gamma-induced surface expression but not TNF-alpha-induced expression. We found that N-acetyl-L-cysteine treatment reduced ICAM-1 mRNA levels when keratinocytes were stimulated with either IFN-gamma or TNF-alpha; however, pyrrolidine dithiocarbamate and alpha-tocopherol had no effect on either IFN-gamma- or TNF-alpha-induced ICAM-1 mRNA levels. Our results indicate that reactive oxygen species may be involved in the skin inflammatory process by increasing epidermal ICAM-1 expression and that some antioxidants may be effective in suppressing the epidermal ICAM-1 expression induced by reactive oxygen species and cytokines in inflammatory skin diseases.

Human aortic endothelial cells express the type I but not the type II receptor for interleukin-1 (IL-1).

Endothelial cells (EC) are very responsive to the proinflammatory cytokine interleukin-1 (IL-1). EC are induced by IL-1 to secrete chemotactic factors and to increase expression of cell surface adhesion molecules leading to increased leukocyte adhesion. Activated EC further contribute to the inflammatory response by secreting additional cytokines. IL-1 interacts with EC through high-affinity cell-surface receptors. However, the low number of receptors present on EC has made characterization difficult. Further, recent evidence has suggested diversity in the responses of EC from different regions of the vascular system. Interested in the effect of IL-1 on early atherosclerotic lesion formation, we have characterized the IL-1 receptors on human aortic endothelial cells (HAEC). Using a direct binding assay, we found that HAEC have 1,000-3,000 IL-1 receptors per cell and bind IL-1 alpha with a Kd of 3.5 x 10(-10) M. We found that a monoclonal antibody specific for the type I receptor completely blocks IL-1 alpha binding. The blocking antibody also completely inhibits the IL-1 induced increase in intracellular adhesion molecule 1 (ICAM-1) expression by HAEC. Using solution hybridization and ribonuclease protection with an antisense probe, a sensitive method for detection of low abundance mRNA species we found that HAEC as well as human umbilical vein EC (HUVEC) have significant levels of mRNA for the type I IL-1 receptor. To test whether HAEC might also contain transcripts for the type II IL-1 receptor, we compared levels of mRNAs by polymerase chain reaction (PCR) amplification of cDNAs reverse-transcribed from total RNA. We found only transcripts for the type I receptor and not the type II receptor in HAEC. Based on this data, we conclude that aortic endothelial cells respond to IL-1 through the type I receptor.

Inhibition of IL-1 beta expression in THP-1 cells by probucol and tocopherol.

The cytokine interleukin-1, IL-1, likely plays an important role in the early stages of atherogenesis. The possible action of probucol and tocopherol on the expression and secretion of IL-1 beta was investigated using the human monocytic leukemia cell line, THP-1. Both probucol and D-alpha-tocopherol inhibit the phorbol ester-induced release of IL-1 beta without altering differentiation. Analysis of IL-1 beta mRNA levels revealed that probucol and tocopherol had an inhibitory effect on the activation of expression of the IL-1 beta gene. The data suggest that the beneficial effects of probucol may be related to inhibition of IL-1 at an early phase of atherosclerotic plaque formation.