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Biomedical subjects

A Nicoll

Publications and source records attributed to A Nicoll.

At least 91 records · Page 5Linked to original sources
PubMed1997

Epidemiology of genital Chlamydia trachomatis in England and Wales.

OBJECTIVE: To describe the recent epidemiology of genital Chlamydia trachomatis infection in England and Wales. DESIGN: Retrospective study of routinely available surveillance datasets and ad hoc prevalence studies. METHODS: Numbers of new cases of genital C trachomatis infection, obtained from the Department of Health and Welsh Office, were combined with the estimated mid-year resident population of England and Wales. Rates were analysed for trend over time using a log linear age period model in GLIM4. Ad hoc prevalence and case finding studies carried out over the past 20 years were critically assessed in terms of study design and testing methodologies. RESULTS: Attendance rates at genitourinary medicine (GUM) clinics were higher for women than men over the period 1989 to 1994 as were the number of laboratory reports. The highest rate of attendance (GUM clinic data) was for women aged 16 to 19 years. There was an overall significant linear decrease in the attendance rates over time for both men (p = 0.0172) and women (p = 0.0000) between 1989 and 1994. There was considerable variation in the prevalence of genital C trachomatis infection detected within different clinical settings, together with a substantial level of asymptomatic infection. CONCLUSIONS: Genital C trachomatis infection is broadly distributed throughout the sexually active population, with a substantial reservoir of asymptomatic infection among those generally perceived to be at low risk of a sexually transmitted infection. Young people, particularly women aged 16 to 19 years, are at highest risk of genital C trachomatis infection. This is of concern since younger women are more susceptible than older women to developing complications of chlamydial infection, such as pelvic inflammatory disease. The broad distribution of infection across all sexually active health service attenders and the high level of asymptomatic infection suggest that a new, screening based, approach to the control of genital C trachomatis infection is required. Recommendations are made as to the epidemiological research required to guide such work.

Adolescent↗
PubMed1997

Direct estimates of prevalent HIV infection in adults in England and Wales for 1991 and 1993: an improved method.

OBJECTIVE: To estimate the number of prevalent HIV infections in England and Wales at the end of 1991 and 1993. METHOD: A direct method was used whereby population estimates derived from the National Survey of Sexual Attitudes and Lifestyle (NATSAL) and prevalence data from the Unlinked Anonymous HIV Prevalence Monitoring Programme (UAPMP) were combined to produce estimates of the number of adults infected and alive in the population. RESULTS: In the population of England and Wales the numbers of prevalent infections for defined transmission categories, at the end of 1993, were as follows: 12,600 through sex between men, 2500 through injecting drug use, and 6900 through heterosexual intercourse. The overall estimate was 22,800 HIV seropositive individuals. CONCLUSIONS: The direct method attempts to provide an estimate of the number of HIV infections using population based survey data. These estimates are consistent with other approaches using independent methods. Such methods are essential for inferring recent HIV incidence, projecting future AIDS cases, and for healthcare planning.

Adolescent↗
PubMed1996

Interpreting HIV seroprevalence data from pregnant women.

HIV prevalence estimates for pregnant women from unlinked anonymous surveys are becoming increasingly available and can be used to determine the prevalence of HIV in women in the same population. The ratio of prevalence in pregnant women to that in all women is influenced by HIV-related risk behaviours that are different for pregnant and nonpregnant women and also by differences in fertility level among infected and uninfected women. This ratio is affected by biases that are likely to be culturally and socially specific. A model is proposed for the qualification and quantification of these biases and hence the estimation of general female population prevalence from serosurveillance data on pregnant women.

Female↗
PubMed1996

Laminar origins of inhibitory synaptic inputs to pyramidal neurons of the rat neocortex.

1. Inhibitory neuron-pyramidal cell interactions were investigated in slices of rat somatosensory cortex in which excitatory synaptic transmission was blocked with bath-applied glutamate receptor antagonists. Local inhibitory neurons were excited by focal pressure ejections of small (approximately 40 pl) volumes of 1-10 mM acetylcholine. 2. The frequency of inhibitory postsynaptic potentials (IPSPs) ("responses per trial' or R/T) declined as the stimulation distance was increased. Inhibitory inputs were most prevalent in layer II/III regular spiking (RS) pyramidal neurons (30 cells) where median R/T was 0.020. In layer V, the median R/T was 0.024 for RS neurons (25 cells), but significantly lower for burst-firing (IB) neurons (17 cells), where median R/T was 0.007 (P = 0.039). 3. IPSPs in individual layer V pyramidal cells were recorded with CsCl electrodes. In eight neurons, spontaneous picrotoxin-sensitive IPSPs were recorded and found to display a wide range of 10-90% rise times (1-34 ms), not correlated with amplitude (0.2-18 mV). For a further ten pyramidal neurons, extracellular stimulating electrodes were placed simultaneously in layers II/III and V/VI in order to evoke pairs of IPSPs whose waveforms were averaged and compared. In seven cells, IPSPs evoked from layer II/III (distal location) had longer 10-90% rise times than IPSPs evoked from layer V/VI stimulating electrodes (proximal location). In addition, "proximal' IPSPs could always be reversed by membrane depolarization whereas "distal' ones could not (n = 4/4). 4. This study showed that pyramid cell-inhibitory neuron interconnections are extensive but their spatial organization varies with cell class and with cortical layer. In addition, pyramidal neurons can receive inhibitory inputs from locations on their apical dendrites.

Acetylcholine↗
PubMed1996

Continuing transmission of sexually transmitted diseases among patients infected with HIV-1 attending genitourinary medicine clinics in England and Wales.

OBJECTIVE: To determine whether those who are aware of being infected with HIV continue to adopt behaviours that place others at risk of HIV infection. DESIGN: Ongoing survey of current diagnosis of sexually transmitted disease and awareness of HIV infection among patients attending genitourinary medicine clinics. SETTING: Six genitourinary medicine clinics in England and Wales (two in London and four outside) participating in unlinked anonymous HIV serosurveillance during 1990-3. SUBJECTS: All attenders having blood drawn for syphilis serology for the first time during the calendar quarter of attendance. MAIN OUTCOME MEASURES: The proportion of syphilis serology specimens with antibody to HIV-1 detected by unlinked anonymous testing of the residue. The proportion of attenders infected with HIV-1 who remained clinically undetected, and the proportion who had another recently acquired sexually transmitted disease. RESULTS: Of 85441 specimens tested, 2328 (2.7%) were positive for antibodies to HIV-1. About 30% of these specimens were from attenders whose HIV-1 infection remained clinically undetected. HIV-1 infection was found to coexist with another recently acquired sexually transmitted disease in 651 attenders, of whom 522 were homosexual or bisexual men. Of these, 245 (47%) already knew themselves to be infected with HIV-1. This proportion increased between 1990 and 1993. CONCLUSIONS: A considerable proportion of patients infected with HIV-1 are not identified by voluntary confidential HIV testing in genitourinary medicine clinics. Substantial numbers of homosexual or bisexual men attending genitourinary medicine clinics continue to practise unsafe sex despite being aware of their infection with HIV-1.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Impact of incomplete coverage of neonatal dried blood spot screening on estimating HIV-1 seroprevalence.

The aim of this study was to determine the extent to which selective under-coverage of births to mothers more likely to be at risk of HIV-1 infection will result in a significant under-estimation of the true neonatal seroprevalence. Census data, local birth statistics, maternity data and data from the prevalence monitoring programme were used to produce a model to predict the effects of under-coverage in the uptake of neonatal metabolic screening which has been observed in babies with a mother of ethnic group black African. The adjustment factor which allows for under-coverage is the relative inclusion ratio (RIR); the probability that samples from a group at different risk of HIV infection were included in the survey divided by the probability of inclusion for samples from all other babies. The RIR was found to be close to unity (0.97), indicating a minimal bias. Under usual conditions only if the relative inclusion ratio (RIR) declined to values of 0.87 or below would there be a substantial bias. Despite some selective under representation, the results obtained from the Unlinked Anonymous HIV Monitoring Programme Dried Blood Spot Survey would seem to identify levels of prevalence in the population of child-bearing women with a good degree of accuracy and remains a useful tool for resource allocation, planning of services, provision of care and counselling.

Adolescent↗
PubMed1996

The impact of HIV-1 infection on child health in sub-Saharan Africa: the burden on the health services.

HIV-1 infection in sub-Saharan Africa is resulting in substantial child mortality and an increase in the number of sick children presenting to health services. Many of the sick children come to health centres and hospitals, inflating numbers on paediatric wards. The presentations of childhood HIV-1 infection are many and varied so that HIV-1 infection is the new "great imitator' of other conditions. Some other infections are more severe in HIV-1 infected children (specifically bacterial infections and measles). However, there is no clear evidence of consequent rises in the incidence of other childhood infections, though this is likely to be the case of tuberculosis. HIV-1 infected children with other infections often respond to locally available anti-microbials, but may require longer courses. Treatment is problematic because of the impossibility of distinguishing infected from uninfected children and because of shortages of medicines, which are being intensified further by the child and adult HIV-1 epidemics. Severe HIV disease in adult family members is adding to child morbidity and creating substantial orphanhood. Staff fear nosocomial infection, while simultaneously experiencing falling personal incomes and lacking resources to care for their patients. Substantial numbers of trained staff are being lost because of HIV-1 caused disease and death. The reality of HIV-1 infection through breast-feeding is not yet appreciated. When this becomes generally apparent, there is a risk that a lethal increase in bottle feeding could occur in some areas. Reduction in the number of new paediatric HIV-1 infections in sub-Saharan Africa can be achieved only by ameliorating the adult HIV-1 epidemic, reducing unnecessary blood transfusions and ensuring a safe blood supply.

Adult↗
PubMed1995

Impact of improved treatment of sexually transmitted diseases on HIV infection in rural Tanzania: randomised controlled trial.

A randomised trial was done to evaluate the impact of improved sexually transmitted disease (STD) case management at primary health care level on the incidence of HIV infection in the rural Mwanza region of Tanzania. HIV incidence was compared in six intervention communities and six pair-matched comparison communities. A random cohort of about 1000 adults aged 15-54 years from each community was surveyed at baseline and at follow-up 2 years later. Intervention consisted of establishment of an STD reference clinic, staff training, regular supply of drugs, regular supervisory visits to health facilities, and health education about STDs. 12,537 individuals were recruited. Baseline HIV prevalences were 3.8% and 4.4% in the intervention and comparison communities, respectively. At follow-up, 8845 (71%) of the cohort were seen. Of those initially seronegative, the proportions seroconverting over 2 years were 48 of 4149 (1.2%) in the intervention communities and 82 of 4400 (1.9%) in the comparison communities. HIV incidence was consistently lower in the intervention communities in all six matched pairs. Allowing for the community-randomised design and the effects of confounding factors, the estimated risk ratio was 0.58 (95% CI 0.42-0.79, p = 0.007). No change in reported sexual behaviour was observed in either group. We conclude that improved STD treatment reduced HIV incidence by about 40% in this rural population. This is the first randomised trial to demonstrate an impact of a preventive intervention on HIV incidence in a general population.

Adolescent↗
PubMed1995

An investigation assessing the fraction of human immunodeficiency virus infection attributable to ethnic group variations in risk.

Considerable speculation and a recent publication has suggested that much of the human immunodeficiency virus (HIV-1) infection in the subset of the UK population represented by women having babies in Metropolitan London is substantially imported from Africa. Other data are supportive of this hypothesis. Ades et al. (1992) concluded that the fraction of HIV seroprevalence, identified in a large London-based study using neonatal blood from the dried blood spots on Guthrie cards, attributable to mothers born in Africa was 92.4% with 95% CI: 82-100%. This is an important observation which requires confirmation. This paper reports on an attempt to do this with closely similar methodology using the Unlinked Anonymous Survey (UAS) of HIV-1 seroprevalence in pregnant women attending antenatal centres, together with data from the Office of Population Censuses and Surveys (OPCS) on the country of origins of mothers delivering in 1991 at the 15 London centres included in the UAS. As in Ades' analysis there appeared to be a strong association between centre prevalences and the proportions of women of African origin delivering at those centres. This was consistent with a high fraction of seroprevalence attributable to such women, but it was also clear that the assumptions required for the estimation of the attributable fractions were not fully met. Analyses modified to justify the assumptions produced attributable fraction estimates ranging from 44% to 96% with lower 95% confidence limits 20% or less.(ABSTRACT TRUNCATED AT 250 WORDS)

Africa↗
PubMed1995

A community trial of the impact of improved sexually transmitted disease treatment on the HIV epidemic in rural Tanzania: 1. Design.

OBJECTIVE: To describe the rationale and design of a randomized trial of the impact of improved services for the treatment of sexually transmitted diseases (STD) on the incidence of HIV infection in Mwanza Region, Tanzania. METHODS: The likely impact of improved STD treatment services on HIV incidence, and the need for empirical information on the effectiveness of this intervention strategy, are discussed. The rationale and design of such an intervention programme in Mwanza Region, and of a community-randomized trial to measure the impact of the programme on HIV and other STD, are presented. Problems in the design and interpretation of the trial are reviewed. RESULTS: Results of the baseline survey of the cohort of over 12,000 adults in 12 communities are presented in a companion paper. CONCLUSION: There is an urgent need for effective preventive measures against the HIV epidemic in sub-Saharan Africa and other developing regions. Improved STD treatment has been promoted as a potentially effective strategy, but there is little empirical information on its impact. The trial in Mwanza Region is the first randomized study of this intervention and should provide valuable data for health policy makers.

Adult↗
PubMed1995

How much paediatric HIV infection could be prevented by antenatal HIV testing?

OBJECTIVE: To estimate the reduction in the number of children infected with HIV that might be achieved by extending the provision of voluntary antenatal HIV testing. This effect would be mediated by increased numbers of women infected with HIV who receive an intervention to reduce the risk of vertical transmission (for example, zidovudine or caesarean section delivery), who use an alternative to breast feeding, or whose pregnancy is terminated. SETTING: London, United Kingdom. METHODS: Relevant data were derived from neonatal seroprevalence studies, obstetric and paediatric reporting schemes, and review of external information. Sensitivity analyses were performed for certain parameters. RESULTS: Of 106,000 births annually in London, an estimated 169 are to women infected with HIV whose infection is not currently recognised before pregnancy. An estimated 28-33 children born to these women will be infected. Precise prediction of the number of paediatric HIV infections that could be prevented is difficult because of uncertainty in certain factors, particularly the uptake of antenatal testing and the efficacy and acceptability of interventions to reduce prenatal or perinatal transmission. If a testing programme detected 70% of infected women, none of whom opted for a termination but all of whom exclusively bottle fed and received an intervention which halved the risk of transmission, about 12-16 (42-46%) paediatric HIV infections would be prevented annually. CONCLUSIONS: The estimated cost of preventing each paediatric infection is high, but this should be seen in the context of the lifetime health and social care costs for a child infected with HIV. The feasibility of selective testing should be considered when formulating policies on antenatal HIV testing. Programmes that are introduced should be audited to obtain better estimates of costs and benefits.

Bottle Feeding↗
PubMed1994

Survey of human immunodeficiency virus infection among pregnant women in England and Wales: 1990-93.

We report on the first four years (1990-93) of a survey within the national HIV prevalence monitoring programme. The survey's objective is to monitor the prevalence of infection with the human immunodeficiency virus (HIV) in pregnant women in London and elsewhere in England. The survey--based in forty centres that offer antenatal care in London, Greater Manchester, West Yorkshire, and adjacent non-metropolitan areas--uses repeated cross sectional serosurveillance for anti-HIV-1 and 2 and the unlinked anonymous test method on blood left over from specimens collected for antenatal screening for immunity to rubella. The seroprevalence of HIV-1 ranged from 0.007% (1 in 14,530) in non-metropolitan areas, to 0.011% (1 in 8790) in metropolitan areas outside London, and 0.23% (1 in 440) in London. Evidence of HIV-2 infection was found in only four specimens, in London (1 in 50,300). The seroprevalence of HIV-1 in London varied more than tenfold between centres, from 0.03% (1 in 3190) to 0.51% (1 in 200). The highest prevalence of infection was in London in women aged between 20 and 30 (0.30%; 1 in 335). The seroprevalence in London centres rose from 0.18% in 1990 (1 in 560) to 0.26% in 1993 (1 in 390) and the rise was significant in all age groups. If voluntary confidential HIV testing (with counselling) among pregnant women in England were to be promoted, its cost effectiveness would be greater if focused on particular centres that provide antenatal care in London.

Adult↗