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D L Thomas

Publications and source records attributed to D L Thomas.

At least 19 recordsLinked to original sources
PubMed1996

Occupational risk of hepatitis C infections among general dentists and oral surgeons in North America.

PURPOSE: To assess the occupational risk of hepatitis C virus (HCV) infection among dental personnel. METHODS: Three hundred forty-three oral surgeons and 305 general dentists were recruited at national meetings of the American Dental Association and matched by gender, age, years of practice, and location of practice. Each participant completed a detailed questionnaire designated to measure occupational risk of blood-borne infections and supplied a sample of blood. Antibodies to HCV (anti-HCV) were assessed by second-generation enzyme immunoassay and recombinant immunoblot assay. As a marker of occupational exposure to blood-borne viruses, hepatitis B virus (HBV) surface antigen and antibodies to HBV surface and core antigens were measured by enzyme immunoassay. RESULTS: Anti-HCV was found in 2.0% of oral surgeons and 0.7% of general dentists (odds ratio [OR] = 3.2, P = 0.133). Anti-HCV was more prevalent (P < 0.01) in dental personnel who were older, had more years of practice, and had serologic markers of HBV infection. Serologic markers of HBV infection were found in 7.8% of general dentists and 21.2% of oral surgeons (OR 3.1, P < 0.001). CONCLUSIONS: These data confirm high rates of HBV infection among dental personnel, but suggest that the risk of HCV infection is considerably lower.

Adult↗
PubMed1995

Sexual transmission of hepatitis C virus among patients attending sexually transmitted diseases clinics in Baltimore--an analysis of 309 sex partnerships.

The prevalence of antibodies to hepatitis C virus (anti-HCV), the behavioral and laboratory-derived risk factors for anti-HCV, and the quantity and homology of HCV RNA were assessed among 1039 non-injection drug-using sexually transmitted disease (STD) patients representing 309 sex partnerships. Thirty-seven (7%) of 555 males and 19 (4%) of 484 females had anti-HCV. In logistic regression analyses, factors associated with anti-HCV included age (P < .001), greater numbers of lifetime sex partners (P = .023), human immunodeficiency virus infection (P < .001), Trichomonas infection (P < .001), cigarette smoking (P < .001), and male homosexual exposure (P = .012). Among couples, females whose sex partners were anti-HCV positive were 3.7 times more likely to have anti-HCV than females whose sex partners were anti-HCV negative (P = .039). The proportion of RNA homology between anti-HCV positive females and their male partners (94%) was higher than among randomly selected patients (82%). Sexual transmission of HCV may contribute to the high prevalence of anti-HCV reported in urban settings.

Adolescent↗
PubMed1995

Correlates of hepatitis C virus infections among injection drug users.

Injection drug users are at high risk for hepatitis C virus (HCV) infection. In Baltimore, Maryland, the prevalence of anti-HCV is greater among injection drug users who are black, human immunodeficiency virus (HIV) infected, have injected longer, have injected more frequently, and have injected cocaine than among other injection drug users. HCV infection occurs quickly after the initiation of injecting illicit drugs, with 78% of study participants anti-HCV positive after 2 years of injecting. The prevalence of anti-HCV among injection drug users does not appear to be related to socioeconomic factors or sexual practices. Some injection drug users remain free of anti-HCV even after years of injecting and serologic evidence of other bloodborne pathogens. Some of these injection drug users have HCV infection, demonstrated by HCV RNA in their sera. However, the basis for viral persistence in the absence of anti-HCV and for the absence of HCV infection in long-term drug users is not known. Further studies are indicated to determine the mechanism or mechanisms for the absence of anti-HCV in persons exposed to the virus, because the biologic basis for this condition may elucidate the elements missing in the immune response of the majority of HCV-exposed persons who acquire persistent infection. In addition, interventions to prevent HCV infections should be applied in populations at risk for injection drug use early or before drug use begins.

Adolescent↗
PubMed1995

Mechanism of cellulose synthesis in Agrobacterium tumefaciens.

Extracts of Agrobacterium tumefaciens incorporated UDP-[14C]glucose into cellulose. When the extracts were fractionated into membrane and soluble components, neither fraction was able to synthesize cellulose. A combination of the membrane and soluble fractions restored the activity found in the original extracts. Extracts of cellulose-minus mutants showed no significant incorporation of UDP-glucose into cellulose. When mixtures of the extracts were made, the mutants were found to fall into two groups: extracts of mutants from the first group could be combined with extracts of the second group to obtain cellulose synthesis. No synthesis was observed when extracts of mutants from the same group were mixed. The groups of mutants corresponded to the two operons identified in sequencing the cel genes (A. G. Matthysse, S. White, and R. Lightfoot. J. Bacteriol. 177:1069-1075, 1995). Extracts of mutants were fractionated into membrane and soluble components, and the fractions were mixed and assayed for the ability to synthesize cellulose. When the membrane fraction from mutants in the celDE operon was combined with the soluble fraction from mutants in the celABC operon, incorporation of UDP-glucose into cellulose was observed. In order to determine whether lipid-linked intermediates were involved in cellulose synthesis, permeablized cells were examined for the incorporation of UDP-[14C]glucose into material extractable with organic solvents. No radioactivity was found in the chloroform-methanol extract of mutants in the celDE operon, but radioactive material was recovered in the chloroform-methanol extract of mutants in the celABC operon. The saccharide component of these compounds was released after mild acid hydrolysis and was found to be mainly glucose for the celA insertion mutant and a mixture of cellobiose, cellotriose, and cellotetrose for the celB and celC insertion mutants. The radioactive compound extracted with chloroform-methanol form the celC insertion mutant was incorporated into cellulose by membrane preparations from celE mutants, which suggests that this compound is a lipid-linked intermediate in cellulose synthesis.

Agrobacterium tumefaciens↗
PubMed1995

High prevalence of hepatitis C in Egyptian patients with chronic liver disease.

The highest prevalence rates of hepatitis C virus infection in the world have been recently reported among Egyptian blood donors and frequent recipients of transfusions and other blood products. This is the first report, however, demonstrating hepatitis C as the most frequent association with chronic liver disease in Egypt. Of 1023 patients referred to the Liver Institute in Menoufia governorate for evaluation of chronic liver disease, 752 (73.5%) had antibodies to hepatitis C compared with 168 (16.4%) with hepatitis B surface antigen. Hepatitis C antibody was more common in patients with active schistosomiasis and patients without hepatitis B surface antigenaemia. Of 100 patients having liver biopsies, histological findings consistent with chronic viral hepatitis or its complications were found in 89 and antibody to hepatitis C was present in 75 (84.3%) of these patients with chronic hepatitis, active cirrhosis or hepatocellular carcinoma. These data pointing to the importance of hepatitis C as a cause of chronic liver disease in Egypt emphasise the necessity of studies delineating its routes of transmission in this country.

Chronic Disease↗
PubMed1995

Performance of hair breeds and prolific wool breeds of sheep in southern Illinois: lamb production of F1 adult ewes.

Two- and three-year-old F1 crossbred ewes produced from Suffolk and Targhee dams and sires of the prolific wool breeds of Finnsheep, Combo-6, and Booroola Merino and the hair breeds of St. Croix and Barbados were pasture-mated to Dorset rams over a 4-yr period at the Dixon Springs Agricultural Center in Southern Illinois. Booroola Merino sires were homozygous for the FecB allele for high number of ovulations. The effects of age of ewe, sex of lamb (where appropriate), breed of dam, and breed of sire on condition score, breeding weight, ovulation rate, breeding to lambing interval, fertility, prolificacy, lamb survival, weaning weight, and ewe productivity were estimated. All traits were analyzed using mixed-model methodology. Crossbred ewes from Suffolk dams had a higher (P < .01) condition score, heavier (P < .01) breeding weight, higher (P < .01) ovulation rate, shorter (P < .01) breeding to lambing interval, greater (P < .01) prolificacy, heavier (P < .01) lambs at weaning, and greater (P < .05) ewe productivity than crossbred ewes from Targhee dams. Ewes from hair-breed sires had lighter (P < .01) breeding weight, lower (P < .05) ovulation rate, shorter (P < .05) breeding to lambing interval, higher (P < .05) fertility, higher (P < .05) lamb survival, lower (P < .10) lamb weaning weight, and higher (P < .05) ewe productivity than ewes sired by the prolific wool-breed rams. The breed of sire x breed of dam interaction was a significant source of variation for breeding weight, fertility, lamb survival, and ewe productivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1994

Hepatitis C, hepatitis B, and human immunodeficiency virus infections among non-intravenous drug-using patients attending clinics for sexually transmitted diseases.

The seroprevalences of and risk factors for hepatitis C virus (HCV), hepatitis B virus (HBV), human immunodeficiency virus (HIV), and syphilis were determined among 1257 consecutive non-intravenous drug-using patients attending Baltimore sexually transmitted diseases clinics: 122 (9.7%) had antibodies to HCV (anti-HCV), 192 (15.3%) had antibodies to HBV (anti-HBc), 44 (3.5%) had antibodies to HIV (anti-HIV), and 60 (4.8%) were seropositive for syphilis. For males, independent predictors of anti-HCV were age > 29 years and lack of condom use in the month before their visit. Males with any one serologic marker (anti-HCV, anti-HBc, anti-HIV, or syphilis) were more likely to have each of the other markers. For females, anti-HCV was independently associated with age > 29 years and > 1 male sex partner in the prior month. Females with anti-HIV or anti-HBc were more likely to have anti-HCV. These observations among non-intravenous drug-using patients suggest that sexual transmission of HCV may occur.

Adolescent↗
PubMed1994

Association of hepatitis C virus infection with false-positive tests for syphilis.

The prevalence of false-positive reactions for syphilis (reactive rapid plasma reagin [RPR] test and nonreactive fluorescent treponemal antibody absorption [FTA-ABS] test) among patients at sexually transmitted disease (STD) clinics was assessed to evaluate the association between false-positive RPR reactions and hepatitis C virus (HCV) infections. Among 2672 patients, 400 (15.0%) had antibodies to HCV (anti-HCV) and 254 (9.5%) had a reactive RPR test. Of the 254 reactive RPR tests, 231 (90.1%) were also positive by FTA-ABS, leaving 23 false-positive RPR reactions. After excluding the 231 patients with positive FTA-ABS tests, false-positive RPR tests were found in 9 (2.7%) of 330 anti-HCV-positive patients compared with 14 (0.6%) of 2154 anti-HCV-negative participants (relative risk, 4.5; 95% confidence interval, 1.9-10.9; P = .0017). These data demonstrate that HCV infection is associated with false-positive RPR test results. However, because of the high prevalence of syphilis among STD patients, the RPR test remains a strong indicator of syphilis in this setting.

Adolescent↗
PubMed1994

A comparison of normal and nonnormal mixed models for number of lambs born in Norwegian sheep.

A comparison of linear (LM), threshold (TM), and Poisson (PM) mixed models for genetic analysis of number of lambs born (NLB) from 1-yr-old ewes was conducted using 37,718 and 18,633 records of two Norwegian breeds, Dala and Spaelsau, respectively. Models fitted included flock-year as a fixed effect and the random effect of sire. In the Poisson model, the residual variation was assumed to be Poisson, whereas it was normal in LM and multinomial in TM. The models were compared with respect to goodness of fit, predictive ability, and ranking of sires. Goodness of fit and predictive ability were assessed via the mean squared error and the correlation between observed NLB and fitted (predicted) values. Predictive ability was evaluated by estimating effects of sire and flock-year using a random half of the data and then using these estimates to predict records on the other half of the data. The heritability of NLB for Dala was estimated to be .20, .39, and .08 with LM, TM, and PM, respectively. For Spaelsau, corresponding estimates were .12, .26, and .00, respectively. In the PM, problems of low or zero estimates of sire variances were encountered. Hence, an alternative sire variance (PM-L) was approximated from the heritability estimated on the outward scale by REML. All models performed similarly with respect to goodness of fit, predictive ability, and ranking of sires. The TM was very slightly better for both breeds, but the PM and PM-L seemed clearly poorer than TM and LM. An approximate test rejected the hypothesis that the conditional distribution of NLB was Poisson.

Animals↗
PubMed1994

Electromagnetic scanning to predict lamb carcass composition.

The electromagnetic scanner generates a constant, low-level electromagnetic field (2.5 MHz) within a large plexiglass tube. The amount of electromagnetic (EM) energy transferred (to the carcass) is highly related to lean tissue. A plot of the absorption units over distance can be used to assess the total mass of lean tissue and of the respective primal cuts. The difference in curve height between two points (D), peak phase absorption, and linear carcass measurements (pre-rigor, HCWT or post-rigor, CWT carcass weight, and carcass length, LENG) were used to predict total dissected lean (TOTLEAN), dissected leg lean (LEGLEAN), and percentage of dissected carcass lean (PERLEAN). Twenty-one pre-rigor and 22 post-rigor (24 h chill) lamb carcasses, average weight 26.8 (+/- 4.2 kg) and 26.4 (+/- 4.1 kg) kg, respectively, were evaluated from measurements of total body electrical conductivity (TOBEC). Two geometric orientations were tested for statistical accuracy in this study: A) each carcass entered the EM tunnel rear leg first, on its left lateral side, neck facing the right side of the tunnel; and B) each carcass entered the EM tunnel rear leg first, breast down, and neck up. Orientation A proved more statistically efficient for pre-rigor carcasses, and orientation B was more desirable for post-rigor carcasses. Multiple-regression models involving HCWT, LENG, and a single D measure accounted for 98.0 and 95.0%, respectively, of the total variation in pre-rigor carcass TOTLEAN and LEGLEAN in A.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

High seroprevalence of hepatitis C infection among risk groups in Egypt.

High prevalence rates of hepatitis C virus (HCV) were recently reported among Egyptian blood donors. To confirm these observations and estimate the magnitude of HCV infection in this country, we determined the prevalence of antibodies to HCV (anti-HCV) in samples collected in 1992 from seven different populations of children and adults living in Egypt. Anti-HCV was found in 12.1% of rural primary schoolchildren, 18.1% of residents of a rural village, 22.1% of army recruits, 16.4% of children with hepatosplenomegaly, 54.9% of hospitalized, multitransfused children, 46.2% of adults on hemodialysis, and 47.2% of adults with chronic liver disease or hepatoma. Age-related prevalence of anti-HCV in a random sample of 270 inhabitants of a rural village increased progressively from zero in those 5-10 years of age to 41% in adults greater than the age of 50. Although the increased prevalence of anti-HCV among children and adults with parenteral exposures and chronic liver disease was expected, the prevalence of anti-HCV among persons representing the general population of Egypt was strikingly high. These data demonstrate the magnitude of HCV infection and its importance in chronic liver disease in Egypt. Future studies are needed to determine the routes of transmission of HCV in this country.

Adolescent↗
PubMed1994

Modernization theory revisited: a cross-cultural study of adolescent conformity to significant others in Mainland China, Taiwan, and the USA.

This paper examines modernization theory's explanation of adolescent conformity behavior to determine patterns in three different cultural settings. Questionnaire survey data were collected from college students in mainland China, Taiwan, and the U.S. LISREL models were used to analyze the data. It was fund that modernization theory was not well supported by the data. Analyses of the findings suggested that modernization theory tests with cross-cultural data should take into consideration cultural characteristics, since much of human behavior is culturally determined. Contrary to modernization theory's predictions, the social institution of education is less important, but religion is highly valued in American society, while the reverse was found in the two Chinese societies.

Adolescent↗
PubMed1993

Hot tub legionellosis. Legionnaires' disease and Pontiac fever after a point-source exposure to Legionella pneumophila.

Legionella pneumophila is associated with outbreaks of either Pontiac fever, a self-limited influenzalike condition without pneumonia, or Legionnaires' disease, a severe pneumonic disease affecting elderly or immunocompromised individuals. An outbreak of both Legionnaires' disease and Pontiac fever after a point-source exposure to L pneumophila was studied. Our observations demonstrated the spectrum of illness that L pneumophila may cause and emphasized the importance of host factors in affecting the expression of infection.

Adult↗
PubMed1993

Viral hepatitis in health care personnel at The Johns Hopkins Hospital. The seroprevalence of and risk factors for hepatitis B virus and hepatitis C virus infection.

BACKGROUND: Health care personnel are at increased risk of occupational acquisition of hepatitis B virus (HBV) infection. While effective vaccination for HBV is widely available, the prevalence of HBV and vaccine acceptance in hospital personnel have not been recently assessed. In addition, hepatitis C virus (HCV) is a newly recognized cause of parenterally acquired hepatitis, and the risk of HCV transmission to health care personnel remains unclear. METHODS: From April to December 1991, health care personnel at The Johns Hopkins Hospital, Baltimore, Md, were offered anonymous testing for HBV and HCV and were asked to complete a confidential questionnaire. Serum samples were tested for HBV surface antigen and antibodies to HBV core antigen, HBV surface antigen, and HCV. Seroprevalence rates were compared with those detected in local blood donors during the same year. RESULTS: Antibodies to HBV core antigen were found in 59 (6.2%) of 943 health care workers compared with 1879 (1.8%) of 104,239 local blood donors (P < .001). In contrast, antibodies to HCV were found in seven (0.7%) of 943 health care workers and 0.4% of local blood donors (P = .10). Infection with HBV was associated with age (> or = 33 years) (P < .001), black race (P < .001), type of health care worker (nurse) (P = .02), 10 ore more years of clinical employment (P = .003), and lack of HBV vaccination (P < .001). After logistic regression, only absence of HBV vaccination was independently associated with HBV infection (P < .001). CONCLUSION: These data suggest that the prevalence of HCV infection in health care personnel at The Johns Hopkins Hospital is similar to that observed in local blood donors, and that HBV may be more efficiently transmitted than HCV in the health care setting. Efforts to vaccinate health care personnel against HBV should be vigorously pursued since 23% remain unvaccinated after 9 years of HBV vaccine availability.

Adult↗
PubMed1993

Epidemiology of hepatitis E virus infection in Turkey.

The seroprevalence and risk factors for infection with hepatitis E virus (HEV) were analysed in five regions of Turkey, where one-third of acute hepatitis cases are non-A, non-B. Antibodies to HEV (anti-HEV) were found in 80 (5.9%) of 1350 subjects. Independent predictors of anti-HEV were age over 25 years, less than elementary education, antibodies to hepatitis C virus, and residence in the warmest region (Adana). Whereas none of 105 subjects in the second decade of life were HEV seropositive, 17 (3.7%) of 464 and 28 (9.1%) of 308 of those in the third and fourth decades of life, respectively, had anti-HEV (p < 0.001). These data demonstrate that in Turkey HEV is more prevalent in warmer regions and in adults, beginning in the third decade of life.

Adult↗
PubMed1993

60 Hz magnetic field acts as co-promoter in focus formation of C3H/10T1/2 cells.

Disruption of communication between transformed cells and normal cells is involved in tumor promotion. We have tested the hypothesis that 60 Hz electromagnetic (EM) field exposures and a chemical tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) are co-promoters that enhance focus formation of transformed cells in co-culture with normal cells. EM field exposures alone did not affect the growth curves of parental C3H/10T1/2 fibroblasts or daughter mutant cells, UV-TDTx10e. Furthermore, EM field exposures alone did not promote focus formation of mutant cells in co-culture with parental cells under the conditions tested. However, EM field exposures co-promoted with TPA by increasing focus formation in co-culture. Cell cultures were exposed to an EM field in custom-built solenoidal incubators. The field exposures were 1.0 Gauss in a schedule of 1 h epochs four times daily for 28 days. Video image analysis of three independent experiments showed that field-exposed cultures produced 1.9-fold more foci than sham-exposed cultures when treated with TPA. The total area of foci per dish increased 2.2-fold and the number of cells in stained foci increased 2.3-fold. In a TPA dose-response, focus formation began at 3 ng/ml with no difference between field-exposed and sham-exposed co-cultures. However, at the TPA concentrations of 10, 20, 40, 50 and 100 ng/ml EM field exposures enhanced focus formation by an average of 150%. This study suggests that chronic intermittent exposures to a 60 Hz EM field and a chemical tumor promoter influenced membrane-related events by co-promoting focus formation.

Animals↗