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Biomedical subjects

S J Clark

Publications and source records attributed to S J Clark.

At least 109 records · Page 6Linked to original sources
PubMed1994

High sensitivity mapping of methylated cytosines.

An understanding of DNA methylation and its potential role in gene control during development, aging and cancer has been hampered by a lack of sensitive methods which can resolve exact methylation patterns from only small quantities of DNA. We have now developed a genomic sequencing technique which is capable of detecting every methylated cytosine on both strands of any target sequence, using DNA isolated from fewer than 100 cells. In this method, sodium bisulphite is used to convert cytosine residues to uracil residues in single-stranded DNA, under conditions whereby 5-methylcytosine remains non-reactive. The converted DNA is amplified with specific primers and sequenced. All the cytosine residues remaining in the sequence represent previously methylated cytosines in the genome. The work described has defined procedures that maximise the efficiency of denaturation, bisulphite conversion and amplification, to permit methylation mapping of single genes from small amounts of genomic DNA, readily available from germ cells and early developmental stages.

5-Methylcytosine↗
PubMed1994

An early death.

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Adult↗
PubMed1994

Unsuspected primary human immunodeficiency virus type 1 infection in seronegative emergency department patients.

To estimate the number of recently infected patients in the window period before human immunodeficiency virus type 1 (HIV-1) seroconversion among patients seeking medical care, randomly selected adults presenting to an inner city emergency department were tested for HIV-1 antibody and p24 antigen. Of 2300 patients enrolled, 180 (7.8%; 95% confidence interval [CI]: 6.7%-8.9%) were Western blot (WB)-positive for HIV-1 antibodies. Of 2120 antibody-negative or WB-indeterminate patients, none of whom were identified on clinical grounds as having primary HIV-1 infection, 6 (0.28%; CI, 0.07%-0.51%) were p24 antigen-positive with serologies consistent with primary HIV-1 infection. Of these 6, 3 were seronegative even with third-generation antibody ELISA. HIV-1 infection in these 6 patients was further confirmed by polymerase chain reaction amplification of virion-associated RNA in serum demonstrating 10(4)-10(5) virions/mL. With 40,000 new HIV-1 infections in the United States annually, approximately 750 persons with undiagnosed primary HIV-1 infections may seek primary health care in any given week in the United States. Testing for viral antibodies alone will fail to detect a large proportion of these persons. Thus, early identification by p24 antigen testing may be important to diagnose and treat symptomatic illness, implement public health and counseling measures, and arrange appropriate medical follow-up.

Adult↗
PubMed1994

Passive smoking amongst asthmatic children. Questionnaire or objective assessment?

An increasing number of studies have implicated passive smoking as a definite threat to non-smokers' health. Self-reports of smoking status may not always be reliable, particularly in situations where the smoker feels under pressure to give up smoking. In this study questionnaire and salivary cotinine, an objective measure of nicotine exposure, were studied in asthmatic and age-matched control children. We have consequently developed a sensitive assay for cotinine using high performance liquid chromatography (HPLC) to quantitate environmental tobacco smoke (ETS) exposure in a group of 5- to 7-year-old asthmatic and control children. We chose to use mixed unstimulated saliva collected by absorption into dental rolls in the mouth for 5 min. Our modified extraction procedure was highly reproducible with a > 90% retrieval rate of cotinine from spiked saliva. The parents were asked to fill in a questionnaire on atmospheric pollutants to obtain an estimate of declared ETS exposure in the home. Results showed that 31% of the asthmatic patients were exposed to ETS, according to the parents, but by HPLC 69% had been so exposed (n = 19). From the control group the figures were 40% and 50% of patients, respectively. Therefore, an objective assessment is essential as ETS is more ubiquitous than is apparent from the questionnaire alone. Finally, in this small number of individuals our objective assessment demonstrates that ETS exposure is more prevalent in asthmatic children (69%) than age-matched controls (51%).

Asthma↗
PubMed1994

Universal hepatitis B immunization of infants: reactions of pediatricians and family physicians over time.

OBJECTIVE: In November 1991 the Advisory Committee on Immunization Practice (ACIP) recommended universal hepatitis B immunization of infants. In February 1992 the American Academy of Pediatrics (AAP) and in August 1992 the American Academy of Family Physicians (AAFP) issued similar recommendations. The purpose of this study was to assess over time the effectiveness and impact of the dissemination efforts of the ACIP, AAP, and AAFP regarding this new recommendation and to determine the factors affecting its adoption. DESIGN: Cohort survey over time. SETTING: North Carolina. PARTICIPANTS: All 778 pediatricians and a random sample of 300 family physicians in North Carolina were surveyed by mail 3 months after publication of the ACIP recommendation (January/February 1992), but before the AAP and AAFP recommendations. Response rate was 78%. Of these, 83% responded to a follow-up survey 8 months later (October 1992). MAIN OUTCOME MEASURES: Rates of agreement and adoption of the recommendation for universal infant immunization with hepatitis B vaccine; factors affecting agreement and adoption of the recommendation. RESULTS: In the first survey (3 months after the ACIP recommendation) more pediatricians than family physicians were aware of the new recommendation (82% vs 48%), yet only 37% of pediatricians and 23% of family physicians agreed that immunization of all newborns in their practice was warranted. Eight months later, after the AAP and AAFP recommendation, 66% of pediatricians and 32% of family physicians agreed universal immunization was warranted, but still only 53% of pediatricians and 23% of family physicians had adopted it into practice. Factors associated with these low rates of adoption include physician and practice characteristics, cost, perceived need for the vaccine, and aversion to multiple injections. CONCLUSIONS: Federal, AAP, and AAFP efforts have not been effective thus far in fostering widespread agreement and adoption of this recommendation. If this and future vaccine programs are to succeed, research is needed to determine influences on implementation of new recommendations and to address the economic and noneconomic concerns of physicians and parents.

Attitude of Health Personnel↗
PubMed1993

High levels of HIV-1 in plasma during all stages of infection determined by competitive PCR.

Quantitative competitive polymerase chain reaction (QC-PCR) methods were used to quantify virion-associated human immunodeficiency virus type-1 (HIV-1) RNA in plasma from 66 patients with Centers for Disease Control stage I to IVC1 infection. HIV-1 RNA, ranging from 100 to nearly 22,000,000 copies per milliliter of plasma (corresponding to 50 to 11,000,000 virions per milliliter), was readily quantified in all subjects, was significantly associated with disease stage and CD4+ T cell counts, and decreased by as much as 235-fold with resolution of primary infection or institution of antiretroviral therapy. Plasma virus levels determined by QC-PCR correlated with, but exceeded by an average of 60,000-fold, virus titers measured by endpoint dilution culture. Quantitation of HIV-1 in plasma by QC-PCR may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative.

Acquired Immunodeficiency Syndrome↗
PubMed1993

The acute retroviral syndrome and the pathogenesis of HIV-1 infection.

The acute retroviral syndrome associated with primary HIV-1 infection is characterized by clinical signs of immune activation, multi-system dysfunction, and high levels of cell-associated and plasma viremia, p24 antigenemia, and proviral burden. Clinical abnormalities associated with acute HIV-1 infection and measures of viral burden and replication generally decline in concert with seroconversion. Despite clearance of virus, patients experiencing severe forms of the acute retroviral syndrome appear to have a poorer prognosis than patients with asymptomatic primary infection. This accelerated natural history may be due to the virulence of strains causing symptomatic infection, sequelae of initial high-titer viremia and consequent high viral burden, or immune depletion through immunopathologic mechanisms accelerated by strong antigenic stimulus in primary infection. Early intervention with anti-retroviral and immune modulatory agents has the potential to alter the natural history of patients with this syndrome.

Acute Disease↗
PubMed1993

Age-related changes in serum free thyroxine during childhood and adolescence.

The purposes of this study were to reevaluate age-related changes in the concentration of serum free thyroxine (T4) between early infancy and adulthood, and to study the relationship of serum thyrotropin to these changes in free T4. Five hundred thirty-six healthy infants, children, adolescents, and adults between 1 day and 45 years of age were studied. Serum free T4 was determined by direct equilibrium dialysis, thyrotropin by a sensitive immunoassay, and total T4 by radioimmunoassay. Free T4 concentrations were age dependent and differed significantly (p < 0.001) at 1 to 4 days, 2 to 20 weeks, 5 to 24 months, 2 to 7 years, 8 to 20 years, and 21 to 45 years of age. Corresponding free T4 concentrations (mean +/- SEM) were 48.1 +/- 1.5, 20.3 +/- 0.6, 17.0 +/- 0.4, 19.9 +/- 0.4, and 21.2 +/- 0.4 pmol/L (3.74 +/- 0.12, 1.58 +/- 0.05, 1.32 +/- 0.03, 1.55 +/- 0.03, 1.32 +/- 0.03, and 1.65 +/- 0.03 ng/dl), respectively. Age-related reference ranges were determined. Changes in the relationship between serum thyrotropin and free T4 were complex, indicating age-related changes in pituitary thyroid regulation. No correlation existed between concentrations of free T4 and total T4 after the first 13 days of life (r2 < 0.01). We conclude that (1) pediatric free T4 concentrations and free T4-thyrotropin relationships differ from those in adults and (2) age-related changes in total T4 do not indicate age-related changes in either free T4 or thyroid function, after 13 days of age.

Adolescent↗
PubMed1993

Determination of plasma viral load in HIV-1 infection by quantitative competitive polymerase chain reaction.

OBJECTIVES: To better characterize viral load profiles through the course of HIV-1 disease and in response to treatment, and to further evaluate quantitative competitive polymerase chain reaction for measurement of viral load, we extended our comparative evaluation of this and other viral load measurements to a total of 118 patients, representing all stages of HIV-1 disease. DESIGN: For cross-sectional analysis across the spectrum of HIV-1 disease, plasma viral load was evaluated in 112 HIV-1-infected patients by quantitative competitive polymerase chain reaction analysis, plasma p24 antigen assay, plasma immune complex-dissociated p24 antigen assay and an endpoint dilution viral culture. Longitudinal specimens from six additional patients were analyzed, extending from the time of presentation with symptomatic acute HIV-1 infection through up to more than 2 years of follow-up. Longitudinal specimens were also studied for three patients over the period of initiation of zidovudine treatment, for 6 weeks of treatment and following temporary withdrawal of the treatment. METHODS: All measurement techniques were assessed in replicate aliquots of plasma. RESULTS: Quantitative competitive polymerase chain reaction was the most sensitive measure of viral load, and was best correlated with CD4+ T-cell counts. In longitudinally studied patients, this technique also allowed measurement of plasma virus levels throughout the period of follow-up, even when culture and p24 assays became negative following resolution of acute HIV-1 infection. The quantitative competitive polymerase chain reaction was also able to detect rapid and substantial changes in viral load associated with initiation and temporary withdrawal of antiviral treatment. CONCLUSIONS: The quantitative competitive polymerase chain reaction is promising as a sensitive and accurate method for measuring plasma viral load in HIV-1-infected patients, and is useful for following changes in viral load over the natural history of infection and following treatment intervention. The technique is particularly useful for patients with > 200 x 10(6) CD4+ T cells/l, in whom other viral markers are typically negative.

Biomarkers↗
PubMed1993

Second trimester ambulatory blood pressure in nulliparous pregnancy: a useful screening test for pre-eclampsia?

OBJECTIVE: To assess the effectiveness of second trimester 24-hour ambulatory blood pressure measurement as a screening test for pre-eclampsia. DESIGN: Prospective interventional study. SETTING: John Radcliffe Maternity Hospital, Oxford, and Queen Charlotte's and Chelsea Hospital, London. SUBJECTS: One hundred and sixty-two normotensive nulliparous women recruited at hospital booking clinics. INTERVENTION: Ambulatory blood pressure was measured at 18 and 28 weeks gestation using the TM2420 monitor. MAIN OUTCOME MEASURE: The development of pre-eclampsia. RESULTS: Awake systolic and mean arterial pressures were significantly increased (P < 0.02) at 18 weeks in those who later developed pre-eclampsia. Those differences were more apparent at 28 weeks at which time the diastolic pressure was also increased (P < 0.01). At both stages of gestation the higher readings were sustained during sleep so that the awake-sleep differences were similar in relation to each outcome. The group with incipient pre-eclampsia had a significantly faster heart rate at both 18 and 28 weeks (P < 0.002) The sensitivity in predicting pre-eclampsia for a mean arterial pressure of 85 mmHg or greater at 28 weeks was 65%, with a positive predictive value of 31%. The sensitivity and positive predictive value for a test combining a mean arterial pressure of 85 mmHg or greater and a heart rate of 90 bpm or greater were 53% and 45%, respectively. CONCLUSION: Although second trimester ambulatory blood pressure is significantly increased in women who later develop pre-eclampsia, the predictive values for blood pressure alone are low. The efficiency of the test is increased by combining the awake ambulatory heart rate and blood pressure measurement together. If an effective method for preventing pre-eclampsia becomes available (commencing at 28 weeks gestation), then awake ambulatory blood pressure and heart rate may have some clinical value as a screening test.

Adolescent↗
PubMed1993

Reactions of pediatricians to a new Centers for Disease Control recommendation for universal immunization of infants with hepatitis B vaccine.

Despite immunization programs targeting high-risk groups, the incidence of hepatitis B has risen 37% over the last decade with 300,000 new infections and 5000 related deaths now occurring annually in the United States. As a new strategy to control the spread of hepatitis B, the Advisory Committee on Immunization Practices of the Centers for Disease Control (CDC) recommended in November 1991 universal hepatitis B immunization of infants. Details were published in an addendum to Morbidity and Mortality Weekly Report. There was no other federal effort to disseminate this recommendation. On February 14, 1992, the American Academy of Pediatrics (AAP) issued a similar recommendation. The time between the CDC and AAP recommendations presented the opportunity to determine the singular effect on clinical practice of the CDC's dissemination effort. The purpose of this study was to assess (1) the effectiveness of the CDC in disseminating a new immunization recommendation, (2) the effect of the new recommendation on clinical practice, and (3) the degree to which noneconomic barriers may affect adoption of universal hepatitis B immunization. All 778 pediatricians in North Carolina were surveyed by mail 2 to 3 months after publication of the new CDC recommendation. Descriptive statistics, chi 2 analysis, and logistic regression were used to assess the relationship of variables hypothesized to predict physician awareness of and/or agreement with the new recommendation. The response rate was 78%. Although 82% of pediatricians who administer immunizations were aware of the new recommendation, only 32% believed it was warranted in their practices.(ABSTRACT TRUNCATED AT 250 WORDS)

Attitude of Health Personnel↗
PubMed1993

Chondrosarcoma of the cricoid: the role of larynx preservation.

Chondrosarcoma of the cricoid cartilage historically has been treated by total laryngectomy. Recent reports lend support for the role of local excision. We present one case and discuss the surgical management for a 63-year-old patient with excellent results.

Biopsy↗
PubMed1993

Family physician acceptance of universal hepatitis B immunization of infants.

BACKGROUND: The incidence of hepatitis B infection has risen 37% over the last decade; 300,000 new infections and 5000 deaths occur annually in the United States. Because immunization programs that targeted high-risk groups failed to abate this increase, the Centers for Disease Control (CDC) recommended in November 1991 universal hepatitis B immunization of infants. Details were published in an addendum to Morbidity and Mortality Weekly Report. The purpose of this study was to assess (1) the effectiveness of the CDC in disseminating a new immunization recommendation to family physicians, (2) the effect of the new recommendation on clinical practice, and (3) the degree to which noneconomic barriers may affect adoption of universal hepatitis B immunization. METHODS: A random sample of 300 family physicians in North Carolina was surveyed by mail. Descriptive statistics and chi-square analysis were used to assess the relationship of variables hypothesized to predict physician awareness of, and agreement with, the new recommendation. RESULTS: The response rate was 78%. Overall, 48% of family physicians who administered immunizations to children were aware of the new hepatitis B vaccine recommendation. However, only 17% agreed that it was warranted for all newborns in their practice. Twenty-five percent expected more than one half of the parents to refuse three injections at a single well-child visit, a result of adding this vaccine to the current primary immunization schedule. Additionally, 42% expected nurses to resist giving three injections at one visit. CONCLUSIONS: The CDC does not have an effective mechanism for disseminating information to all physicians who care for children. Improved coordination of recommendations between the CDC and relevant specialty societies may help to increase physician adoption of new immunization recommendations in their clinical practice. Additionally, practical concerns of physicians and their patients regarding multiple injections and other practice-relevant issues must be considered when formulating new immunization recommendations, if their implementation is to be successful. Additional research is needed to determine effective methods to disseminate immunization information and to address practical concerns of clinicians.

Adult↗
PubMed1992

Magic bullets.

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Chronic Disease↗
PubMed1992

The influence of ambulatory blood pressure monitoring on the design and interpretation of trials in hypertension.

OBJECTIVE: To describe the reproducibility of diastolic blood pressure (DBP) measurement by clinic and ambulatory monitoring and to evaluate the effects of this reproducibility on the design and interpretation of clinical trials in hypertension research. DESIGN: Prospective single-blind study of repeat measurement reproducibility of blood pressure recording. SETTING: Tertiary referral hospital hypertension clinic. PATIENTS: One hundred untreated mild-to-moderate hypertensive subjects taking 1 month of single-blind placebo. MAIN OUTCOME MEASURES: A single clinic measurement of DBP was poorly reproducible and the results for single DBP estimates taken out of a daytime ambulatory recording were similar. Average ambulatory DBP was much more reproducible, although this improvement depended upon the averaging of many measurements taken throughout the day. CONCLUSIONS: Ambulatory monitoring would decrease antihypertensive trial size by a factor of four or halve the size of detectable DBP difference between treatments. The use of poorly reproducible DBP measurements such as single clinic readings may have led to an underestimation of the risks of minor degrees of blood pressure elevation because of a 'regression dilution' bias. For single clinic DBP readings, we calculate this underestimation to be as much as 69%, and for average ambulatory DBP approximately 20%.

Adult↗