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Biomedical subjects

Mark Davis

Publications and source records attributed to Mark Davis.

At least 19 recordsLinked to original sources
PubMed2007

Barebacking among HIV-positive gay men in London.

OBJECTIVES: The objectives of this study were to examine the extent to which HIV-positive gay men in London intentionally seek unprotected anal intercourse ("barebacking") and the contribution this makes to total sexual risk. STUDY DESIGN: In 2002 to 2003, HIV-positive gay men surveyed in an HIV outpatient clinic or on the Internet were asked whether they had intentionally looked for anal sex without a condom in the previous 12 months. RESULTS: Of 481 men in the clinic, 59 (12.3%) said they had intentionally looked for anal sex without a condom, 34 (7.1%) only with another HIV-positive man and 25 (5.2%) with a man of unknown or discordant HIV status. Overall, 85 men reported unprotected anal intercourse (UAI) with a casual partner of unknown or discordant HIV status; 20 (23.5%) had intentionally looked for UAI with such a partner, whereas the remaining 65 (76.5%) had not. Of 66 men surveyed on the Internet, 32 (48.5%) said they had intentionally looked for anal sex without a condom. CONCLUSION: Although barebackers made a disproportionate contribution to sexual risk, three-fourths of high-risk sex reported by HIV-positive gay men in London was not intentional. The Internet sample overestimated the prevalence of barebacking among HIV-positive gay men because of sampling bias.

Adult↗
PubMed2006

Energetics of xylose decomposition as determined using quantum mechanics modeling.

The decomposition of xylose has been studied using quantum mechanical calculations supported by NMR data. Proposed mechanisms for the decomposition of xylose have been investigated by obtaining the structures and energies of transition states and products. The intent of this study was to understand the experimentally observed formation of furfural and formic acid that occurs during the decomposition of xylose in mildly hot acidic solutions. A mechanism of furfural formation involving the opening of the pyranose ring and subsequent dehydration of the aldose was compared to a direct intramolecular rearrangement of the protonated pyranose. Energies were determined using CBS-QB3, and it was shown that the barriers for dehydration of the aldose were high compared to intramolecular rearrangement. This result suggests that the latter mechanism is a more likely mechanism for furfural formation. The intramolecular rearrangement step results from protonation of xylose at the O2 hydroxyl group. In addition, it has been shown that formic acid formation is a likely result of the protonation of xylose at the O3 hydroxyl group. Finally, solvation of xylose decomposition was studied by calculating energy barriers for xylose in selected water clusters. The mechanisms proposed here were supported in part by 13C-labeling studies using NMR.

Formates↗
PubMed2006

Activity-induced weakness in recessive myotonia congenita with a novel (696+1G>A) mutation.

OBJECTIVE: To investigate the cause of the transient weakness that occurs in recessive myotonia congenita (RMC) following sustained muscle contraction. METHODS: Nerve excitability studies were performed on a 35-year-old male with RMC due to a novel 696+1G>A CLCN1 mutation. The median nerve was stimulated at the wrist and compound muscle action potentials (CMAPs) were recorded from abductor pollicis brevis (APB). Stimulus-response behaviour using two stimulus durations, threshold electrotonus to 100-ms polarizing currents, a current threshold relationship and the recovery of excitability following supramaximal stimulation were recorded at rest. Excitability parameters were also recorded before and after maximal voluntary contraction (MVC) of APB against resistance for 60s. Results were compared to data obtained from 12 normal controls. RESULTS: Baseline axonal excitability parameters were all normal, indicating that axonal function was normal at the point of stimulation. Following one minute of MVC, excitability parameters demonstrated a significant increase in threshold when compared to controls (RMC 54.9%; controls 15.5+/-3.1%). In the RMC patient, this increase in threshold was associated with a 39% reduction in the amplitude of the maximal CMAP, which remained unaffected in controls. CONCLUSIONS: The reduction in maximal CMAP is likely to represent muscle activation failure due to depolarization block, with the increase in threshold possibly reflecting a compensatory attempt by motor axons to overcome prolonged contraction-induced changes in the muscle membrane. SIGNIFICANCE: The prolonged recovery of excitability following sustained muscle contraction is likely to be a contributing factor to symptoms of weakness and fatigue experienced by RMC patients.

Action Potentials↗
PubMed2006

E-dating, identity and HIV prevention: theorising sexualities, risk and network society.

This paper addresses how London gay men use the internet to meet sexual partners, or for e-dating. Based on qualitative interviews conducted face-to-face or via the internet, this research develops an account of how information technologies mediate the negotiation of identity and risk in connection with sexual practice. E-dating itself is a bricolage, or heterogeneous DIY practice of internet-based-communication (IBC). A central aspect of IBC is "filtering" in and out prospective e-dates based on the images and texts used to depict sexual identities. Interpretations and depictions of personal HIV risk management approaches in IBC are framed by the meanings of different identities, such as the stigma associated with being HIV positive. This paper argues for a sexualities perspective in a theory of network society. Further, HIV prevention in e-dating can potentially be addressed by considering the interplay of the HIV prevention imperatives associated with different HIV serostatus identities. There is a case for encouraging more explicit IBC about risk in e-dating and incorporating the expertise of e-daters in prevention activity. There is also a need to rethink traditional conceptions of risk management in HIV prevention to make space for the risk management bricolage of network society.

Adult↗
PubMed2006

Uncertainty and 'technological horizon' in qualitative interviews about HIV treatment.

Highly Active Anti-Retroviral Treatment (HAART) has reduced death and morbidity among people with HIV. However, HAART is not always effective, can produce serious side-effects and implies uncertainty for patients. To address HAART-related uncertainty, 20 qualitative interviews were conducted with gay men with HIV in Glasgow and London. The interviewees were purposively selected to reflect diversity in terms of year of diagnosis, experiences of illness and treatment-related side-effects. The interviews were analysed using the constant comparison method to derive themes. Among those using HAART, analysis identified themes of 'good health', 'illness' and 'loss of confidence'. Uncertainty was managed through a discourse of 'technological horizon' that combined the ongoing innovations of HAART and biographical time. These themes are discussed in terms of the implications for HIV care. In particular, technological horizon provides a basis for the management of uncertainty in the prescribing relationship between patient and clinician.

Adult↗
PubMed2006

Heterosexual men and women who seek sex through the Internet.

Heterosexual women (n = 330), heterosexual men (n = 319) and gay men (n = 331) attending a London HIV-testing clinic in 2002-03 completed a confidential self-administered questionnaire concerning their sexual behaviour and use of the Internet for seeking sexual partners (response rate 70%). One-in-twenty (5%) heterosexual women and one-in-ten (10%) heterosexual men had used the Internet to look for sexual partners in the previous 12 months compared with nearly half (43%) the gay men (P<0.001). Rates of high-risk sexual behaviour with a casual partner were elevated among those who used the Internet to look for sex (compared with those who did not). However, people who looked for sex through the Internet were just as likely to meet their high-risk casual partners offline as online. Our findings suggest that high-risk heterosexual women and men are selectively using the Internet to look for sex rather than the Internet per se leading to riskier sexual behaviour.

Adolescent↗
PubMed2005

Ab initio molecular dynamics simulations of beta-D-glucose and beta-D-xylose degradation mechanisms in acidic aqueous solution.

Ab initio molecular dynamics simulations were employed to investigate, with explicit solvent water molecules, beta-D-glucose and beta-D-xylose degradation mechanisms in acidic media. The rate-limiting step in sugar degradation was found to be protonation of the hydroxyl groups on the sugar ring. We found that the structure of water molecules plays a significant role in the acidic sugar degradation pathways. Firstly, a water molecule competes with the hydroxyl group on the sugar ring for protons. Secondly, water forms hydrogen bonds with the hydroxyl groups on the sugar rings, thus weakening the C-C and C-O bonds (each to a different degree). Note that the reaction pathways could be altered due to the change of relative stability of the C-C and C-O bonds. Thirdly, water molecules that are hydrogen-bonded to sugar hydroxyls could easily extract a proton from the reaction intermediate, terminating the reaction. Indeed, the sugar degradation pathway is complex due to multiple protonation probabilities and the surrounding water structure. Our experimental data support multiple sugar acidic degradation pathways.

Computer Simulation↗
PubMed2005

Gay men who look for sex on the Internet: is there more HIV/STI risk with online partners?

OBJECTIVE: To examine whether the excess risk for HIV and sexually transmitted infection (STI) seen among gay men who look for sex through the Internet occurs with men they meet online (through the Internet) rather than offline (in bars, clubs, etc). METHODS: In 2002-2003, 4225 London gay men were surveyed in an HIV treatment clinic, HIV testing clinic, gyms and on UK Internet sites (gaydar and gay.com). All men completed a self-administered questionnaire concerning Internet use and sexual risk behaviour. Unprotected anal intercourse (UAI) with a partner of unknown or discordant HIV status was classified as non-concordant. RESULTS: Between 40 and 50% of men surveyed in the clinics and gyms used the Internet to look for sex. HIV-positive men who looked for sex through the Internet were more likely to report UAI with HIV-positive casual partners they met online rather than offline (clinic sample: met online only 9.9%, met offline only 3.8%, McNemar P < 0.05). Regardless of HIV status, however, men who looked for sex through the Internet were no more likely to report UAI with non-concordant casual partners they met online than offline (eg, HIV-negative men, Internet sample: met online only 9.7%, offline only 11.1%, McNemar P = 0.6). CONCLUSIONS: In London, HIV-positive gay men appear to meet casual UAI partners of the same status through the Internet. This presents a risk for STI transmission. However, gay men were no more likely to meet casual UAI partners of unknown or discordant HIV status--which presents a risk for HIV transmission--online rather than offline.

Adolescent↗
PubMed2005

Venous ulcers.

Veneous ulcers are extremely common, accounting for a large proportin of all lower extremity ulcers. Due to their chronicity and relatively high prevalence, their impact on the cost of healthcare and the lives of the patients affected is quite significant. There has been progress in understanding the pathophysiology, clinical features, and diagnosis of these ulcers, but the basic principles of care have remained consistent for almost a half century. To allow for optimal healing, it is important to maintain a clean moist wound bed, treat any clinically significant infection, and decrease surrounding edema.

Cost of Illness↗
PubMed2005

Health service use in Rett syndrome.

Rett syndrome is a severe neurodevelopmental disorder affecting girls, caused by mutations in the MECP2 gene. There are no population-based data on the extent and determinants of health service use in this disorder. The population-based registry, the Australian Rett Syndrome database, was the source of phenotype data. This also contains data from mutation screening and X-inactivation studies. Data on retrospective (n = 152) and prospective (n = 162) health service use were collected in 2000 from a questionnaire and a calendar study, respectively. Health service use was highest in younger cases (P = .001) and lowest in cases with milder phenotypes (P < .001). Random X-inactivation was associated with service use (P = .02). Maternal education, phenotype, and individual mutations were determinants of health service use. The use of a retrospective and prospective data set enabled accurate assessment of service use in Rett syndrome. Both genetic and sociodemographic determinants of health service use were identified, with important implications for the optimal and equitable management of children with Rett syndrome.

Adolescent↗
PubMed2005

Differentiating causes of respiratory distress.

Respiratory emergencies will continue to make up a large percentage of our EMS calls. Many of these conditions will be managed in the same fashion early on with a focus on oxygenation and adequate ventilation. Once the ABCs have been stabilized, use your assessment skills to create a differential diagnosis for respiratory distress. Once a field impression has been made, you can better direct a specific treatment. As always, follow your local treatment protocols established by your medical director. Practice your assessment skills and attend as much training as you can on airway and respiratory emergencies.

Diagnosis, Differential↗
PubMed2004

Prevention of type I diabetes transfer by glutamic acid decarboxylase 65 peptide 206-220-specific T cells.

Glutamic acid decarboxylase (GAD) 65 is one of the major pancreatic antigens targeted by self-reactive T cells in type I diabetes mellitus. T cells specific for GAD65 are among the first to enter inflamed islets and may be important for the initiation of autoimmune diabetes. However, we previously reported that nonobese diabetic (NOD) mice transgenic for a T cell antigen receptor (TCR) specific for one of the immunodominant epitopes of GAD65, peptide 286-300 (G286), are protected from insulitis and diabetes. To examine whether other GAD65-reactive T cells share this phenotype, we have generated TCR transgenic NOD mice for a second immunodominant epitope of GAD65, peptide 206-220 (G206). As in G286 mice, G206 mice do not develop islet inflammation or diabetes. When adoptively transferred along with diabetogenic T cells, activated G206 T cells significantly delayed the onset of diabetes in NOD.scid recipients. Both G206 and G286 T cells produce immunoregulatory cytokines IFN-gamma and IL-10 at low levels when activated by cognate antigens. These data suggest that GAD65-specific T cells may play a protective role in diabetes pathogenesis by regulating pathogenic T cell responses. A better understanding of the functions of autoreactive T cells in type I diabetes will be necessary for choosing desirable targets for immunotherapy.

Amino Acid Sequence↗
PubMed2004

The Internet and HIV study: design and methods.

BACKGROUND: The Internet provides a new meeting ground, especially for gay men, that did not exist in the early 1990s. Several studies have found increased levels of high risk sexual behaviour and sexually transmissible infections (STI) among gay men who seek sex on the Internet, although the underlying processes are not fully understood. Research funded by the UK Medical Research Council (2002-2004) provided the opportunity to consider whether the Internet represents a new sexual risk environment for gay and bisexual men living in London. METHODS: The objectives of the Internet and HIV study are to: (i) measure the extent to which gay men living in London seek sexual partners on the Internet; (ii) compare the characteristics of London gay men who do and do not seek sex on the Internet; (iii) examine whether sex with Internet-partners is less safe than with other sexual partners; (iv) compare use of the Internet with other venues where men meet sexual partners; (v) establish whether gay men use the Internet to actively seek partners for unprotected anal intercourse; (vi) determine the potential for using the Internet for HIV prevention. These objectives have been explored using quantitative and qualitative research methods in four samples of London gay men recruited and interviewed both online and offline. The four samples were: (i) gay men recruited through Internet chat rooms and profiles; (ii) HIV positive gay men attending an NHS hospital outpatients clinic; (iii) gay men seeking an HIV test in an NHS HIV testing or sexual health clinic; (iv) gay men recruited in the community. RESULTS: Quantitative data were collected by means of confidential, anonymous self-administered questionnaires (n>4000) completed on-line by the Internet sample. Qualitative data were collected by means of one-to-one interviews (n = 128) conducted either face-to-face or on-line. CONCLUSION: The strength of the Internet and HIV study is its methodological plurality, drawing on both qualitative and quantitative research among online and offline samples, as well as taking advantage of recent advances in web survey design. The study's findings will help us better understand the role of the Internet in relation to gay men's sexual practice.

Adult↗
PubMed2004

Clinical management. Where medicine meets management. Way to go.

When setting up an ICP, invite participation from all relevant healthcare professionals in both primary and secondary care. Gather all research and best practice using national guidelines or best available evidence. Consult patients: they often have knowledge unavailable to medical professionals.

Benchmarking↗
PubMed2004

Web-based behavioral surveillance among men who have sex with men: a comparison of online and offline samples in London, UK.

OBJECTIVE: To compare the characteristics of men who have sex with men (MSM) surveyed online (through gay Internet chat rooms and profiles) and offline (in community venues) in London, UK. METHODS: In February and March 2002, 879 MSM completed a self-administered pen-and-paper questionnaire distributed in central London gyms (offline sample). In May and June 2002, 1218 London MSM completed a self-administered questionnaire online, accessed through Internet chat rooms and profiles on gaydar and gay.com. RESULTS: Compared with men surveyed offline, those surveyed online were significantly less likely to only have sex with men (89 vs. 94%), to be in a relationship with a man (44 vs. 52%), or to have been tested for HIV (68 vs. 80%) (P < 0.001). Men recruited online were also younger (mean age, 34 vs. 36 years) and less likely to have had a higher education (67 vs. 79%) (P < 0.001). However, differences between online and offline samples were less pronounced for HIV-positive men and more pronounced for HIV-negative men and those who had never been tested for HIV. Regardless of HIV status, men recruited online were more likely to report high-risk sexual behavior (i.e., unprotected anal intercourse with a partner of unknown or discordant HIV status) than men surveyed offline (32 vs. 22%, P < 0.001). Men recruited online were also significantly more likely to have used the Internet to look for sex (85 vs. 45%, P < 0.001); for HIV-positive and negative men, seeking sex on the Internet was associated with high-risk sexual behavior (P < 0.01). In multivariate analysis, after controlling for confounding factors, being surveyed online was independently associated with high-risk sexual behavior for HIV-negative and never-tested men (HIV-negative men, adjusted odds ratio for online vs. offline samples, 1.73; 95% CI, 1.23, 2.42; P < 0.01; never-tested men adjusted odds ratio 2.45; 95% CI, 1.40, 4.29; P < 0.01). This was not the case for HIV-positive men (adjusted odds ratio for online vs. offline samples, 1.32; 95% CI, 0.69, 2.50; P = 0.4). CONCLUSION: The Internet offers valuable opportunities for conducting behavioral surveillance among MSM because it reaches some men who may not be easily accessed in the community yet who are at high risk for HIV and sexually transmitted diseases. Comparisons of the social, demographic, and behavioral characteristics of online and offline samples must, however, take into account the confounding effects of HIV status and seeking sex on the Internet.

Adult↗
PubMed2004

Preventing hepatitis C: 'common sense', 'the bug' and other perspectives from the risk narratives of people who inject drugs.

There is little published research about how people who inject drugs are responding to the hepatitis C epidemic. This study seeks to address the prevention of hepatitis C using qualitative interviews with people who inject drugs in London. We explored narratives about risk reduction and hepatitis C in the social and historical context of other risks such as HIV, vein damage and overdose. Themes of the narratives included: the importance of autonomy in the acquisition of safer injecting skills; that safer injection was regarded as 'common sense', normalised and predicated on the risk of HIV; that hepatitis C risk was relativised with HIV risk and thereby seen as less important; and that hepatitis C infection was also seen as unavoidable. These narrative forms represent significant challenges for the management of the hepatitis C epidemic, both in terms of the existing risk reduction efforts designed for HIV and in terms of the articulation of risk reduction for injectors with general public health policy.

Adolescent↗