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Biomedical subjects

R M Anderson

Publications and source records attributed to R M Anderson.

At least 217 records · Page 12Linked to original sources
PubMed1990

Autosomal recessive hydrocephalus with third ventricle obstruction.

Here we report a brother and sister who presented in the neonatal period with hydrocephalus. Ultrasonography showed marked dilatation of the lateral ventricles but not the third ventricle. One child with postnatal onset was shunted and had normal development at 3 years. The other child had severe hydrocephalus at birth and was not treated. Neuropathologic studies demonstrated dilatation of the lateral ventricles and marked narrowing of the posterior part of the third ventricle but no other malformations other than those that result directly from hydrocephalus. The potential for a good prognosis is emphasized.

Cerebral Ventricles↗
PubMed1990

Measuring the attitudes of patients towards diabetes and its treatment.

The following is a study of the general diabetes-related attitudes of 1202 patients with diabetes in Michigan. The instrument used to measure attitudes was a revised version of the Diabetes Attitude Scale (DAS) designed to measure the attitudes of health care professionals. A factor analysis of the revised DAS yielded seven diabetes attitude factors. These factors represented patients' attitude toward: (1) the need for special training in order to provide diabetes care; (2) patient compliance; (3) the seriousness of noninsulin-dependent diabetes (NIDDM); (4) the relationship between blood glucose levels and complications; (5) the impact of diabetes on the patient's life; (6) patient autonomy; (7) team care. Overall, the respondents to this survey displayed attitudes consistent with the current recommendations of health care professionals in the field of diabetes. The revised DAS is an instrument that can be used to measure and compare the attitudes of both health care professionals and patients on a variety of diabetes-related issues.

Attitude of Health Personnel↗
PubMed1990

A guide for assessing a patient's level of personal responsibility for diabetes management.

This paper presents a guide for assessing a diabetic patient's level of personal responsibility. In the general population, high levels of personal responsibility have been shown to be related to psychological well-being and are especially appropriate for chronic disease such as diabetes. With diabetes, patients are required to deliver virtually all of the daily self-care. Successful adaptation to this role is enhanced when patients are able to accept personal responsibility for having and treating their diabetes. The paper describes five levels of personal responsibility starting with the lowest level in which patients feel overwhelmed, hopeless, and helpless and ending with the highest level in which patients accept diabetes as a fact of their lives and fully accept responsibility for it. A discussion of assessing the patient's level of personal responsibility and responding appropriately to patients at different levels is included.

Adaptation, Psychological↗
PubMed1990

Serological study of the epidemiology of mumps virus infection in north-west England.

Serum samples from individuals of a wide age range, collected in northwest England in 1984 and 1986, provide the basis for an analysis of the epidemiology of mumps virus infection. A radial haemolysis test yielding quantitative antibody measurements was used to screen samples for mumps-specific IgG. Analyses of resultant age-seroprevalence profiles, using statistical models, revealed an age-related pattern in the rate of infection per susceptible similar to that observed for other childhood infections. This rate, or force of infection, was low in young children, high in older children, and low in adults. In addition, the serological surveys provide evidence for time-dependent changes (both epidemic and longer-term) in the rate of mumps virus transmission. The longer-term changes, reflected in the pattern of the age-acquisition of specific antibodies, are supported by evidence from case notification data. The implications of temporal changes in incidence to the interpretation and design of serological surveys are considered.

Adolescent↗
PubMed1990

Measles immunization strategies for countries with high transmission rates: interim guidelines predicted using a mathematical model.

This study addresses the problem of measles immunization in communities experiencing unacceptably high numbers of cases in young infants, under circumstances where high dose Edmonston-Zagreb vaccine is not yet available. Where the continued use of standard potency vaccines (eg Schwarz) is unavoidable we have investigated the merits of new policies which aim to offer better protection to children below the currently recommended vaccination age of nine months. These policies are intended for implementation in communities with intense measles transmission. Predictions, spanning five years, using a previously developed mathematical model are presented for two types of potential new policies: a 'switch' to a younger target age, or a 'two-dose' strategy incorporating vaccination at a younger age in addition to the current schedule at nine months. We conclude that a switch in immunization policy to a younger age is of doubtful worth, but that supplementary vaccination at around six months in addition to existing coverage at nine months (ie two-dose policy) is a desirable option.

Age Factors↗
PubMed1990

Reducing the spread of HIV infection in sub-Saharan Africa: some demographic and economic implications.

Any reduction in the rate of spread of HIV infection has consequences for the incidence and demographic effects of AIDS. In this paper, output from a published mathematical model of the dynamics of HIV transmission through heterosexual contact is used to study the implications of reducing HIV transmission on demographic patterns and national health budgets in sub-Saharan Africa. The major conclusion is that both the timing and the effectiveness of reducing HIV transmission are non-linearly related to their potential demographic and economic effects. The analysis emphasizes the benefits to be gained from a concerted effort to reduce the spread of HIV infection as early as possible in the time course of the epidemic.

Africa↗
PubMed1990

The evolutionary dynamics of HIV-1 quasispecies and the development of immunodeficiency disease.

This paper presents a theory to explain the development of immunodeficiency disease after a long and variable incubation period of infection with HIV-1. Two assumptions are central to the theory: (1) mutation via reverse transcription during viral replication can generate viral strains resistant to neutralization by antibodies specific to earlier mutants in a particular host; (2) the virus can kill the CD4-positive lymphocytes that play a role in mounting an immunological attack directed at the virus. The theory is examined via the development of a mathematical model which reveals that an increasing number of antigenically distinct viral strains may overwhelm the immune system of the host. As the viral diversity increases beyond a certain level the immune system is unable to suppress the population growth of all the strains simultaneously. The intuitive explanation of this pattern of model behaviour lies in the assumption that each virus can kill CD4-positive lymphocytes that are specific to any of the viral strains, but each lymphocyte only directs immunological attack against a single viral strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1990

The role related attitudes of physicians, nurses, and dieticians in the treatment of diabetes.

The treatment of diabetes requires role changes for physicians, nurses, dieticians, and patients. The nature of diabetes care results in a diffusion of responsibility for care from physicians to nurses, dieticians, and patients. This responsibility for diabetes treatment is often carried out under the rubric of team care. This study indicates that physicians, nurses, and dieticians with a special interest in diabetes are supportive of their own roles but that physicians tend to see themselves being in charge of diabetes care while nurses and dieticians value patient autonomy more.

Attitude of Health Personnel↗
PubMed1990

The significance of sexual partner contact networks for the transmission dynamics of HIV.

The paper provides a brief review of the significance of heterogeneity in sexual behaviour to the transmission dynamics of HIV and the spread of AIDS. It addresses the formulation of mathematical models to encapsulate variability in the rate of sexual partner change, the structure of networks of sexual partner contact, and age dependency in sexual activity. A particular focus is the significance of high or low preference (or choice) of sexual partners from an individual's own sexual activity class (defined on the basis of partner change rate or other criteria). Numerical studies of model behaviour reveal that a high degree of assortativeness (high level of "like with like" mixing) results in a more rapid initial spread of HIV, a smaller overall epidemic, and the possibility of a multipeak or long and drawn out epidemic, by comparison with those induced by high degrees of disassortativeness (low level of "like with like" mixing) in sexual contact patterns. The structure of a sexual network is shown to be a major determinant of the temporal pattern and magnitude of an epidemic. The demographic impact of HIV in developing countries is also examined in the context of choice matrices based on age as well as sexual activity. The potential demographic impact of AIDS is shown to be enhanced by age dependency in levels of activity (high in the young and lower in older age classes), a male preference for females of younger age, and a higher efficiency of HIV transmission from male to female than vice versa. The paper ends with a discussion of the need for better quantitative data on sexual behaviour.

Adult↗
PubMed1990

Age-dependent sexual behaviour amongst male homosexuals and the transmission dynamics of HIV-1.

The paper describes the development of an age-structured model of the transmission dynamics of HIV-1 in a male homosexual population with age-dependent rates of sexual partner acquisition, and explores the properties of the model by means of numerical methods. Age-dependency in rates of sexual partner change acts to increase the initial growth rate of the epidemic and raises the equilibrium level of endemic infection in the population when compared with the prediction of a model without age structure but with identical initial overall population mean rate of partner acquisition. In addition, age-dependency in sexual activity acts to induce demographic changes in the population where the younger more sexually active males represent an increasing proportion of the population as the epidemic develops over time. One consequence of this is an increase in the overall population mean rate of sexual partner change as a direct result of the mortality induced by AIDS in the older less sexually active classes who acquired infection at a younger age. The results are discussed in relation to the interpretation of current patterns of HIV-1 spread and the acquisition of quantitative information on sexual behaviour.

Adolescent↗
PubMed1990

Loglinear models, sexual behavior and HIV: epidemiological implications of heterosexual transmission.

An analysis is presented of sexual behaviour data from a "random" sample (n = 780) of the adult population of England and Wales. Sex stratified frequency distributions of the reported number of sex partners/time were analysed for heterosexuals, demographic characteristics associated with the number of sex partners/time were identified, and epidemiological parameters (the basic reproductive rate of HIV and the doubling time of the epidemic) were calculated. These analyses suggest that the size of the group at risk for acquiring the virus by heterosexual transmission may be large and that the age of first sexual intercourse (for males and females) is decreasing in younger cohorts. Members of the potential heterosexual at-risk group may be identified by demographic variables such as marital status (males and females) and age (females only), but not by socioeconomic class. The epidemiological implications of our results for the heterosexual transmission of HIV are discussed.

Adolescent↗
PubMed1989

Epidemiological and statistical aspects of the AIDS epidemic: introduction.

In 1988, a government working party studied estimates of incidence and prevalence of numbers of acquired immunodeficiency syndrome (AIDS) cases. They investigated a series of epidemiological, statistical and mathematical problems associated with predicting trends in incidences of AIDS. This paper introduces a series of papers that give a fuller and more technical exposition of the appendixes of that working party report. The papers provide a brief background to the current state of knowledge on the epidemiology of the infection and the disease; a deterministic model for human immunodeficiency virus (HIV) transmission in the male homosexual community in England and Wales is introduced. Back-projection methods are studied in two papers, following the distribution of the incubation period of the disease. The concept of minimum size of the epidemic is introduced. Mathematical functions to describe the spread of HIV infection are refined by using past trends in the incidence of AIDS to estimate values for some parameters. Survival times for AIDS patients from the point of diagnosis are considered and evidence for changes in male homosexual sexual behaviour is studied; lag-time from the point of diagnosis to the report of the case is also examined. There is a comparative analysis of the AIDS epidemic in various European countries. The incubation period of HIV in patients with haemophilia A and B infections and the problems associated with making predictions for different at-risk groups or small subgroups based on geographical area are discussed. Reasons for fluctuation between the number of reported cases from month to month are provided.

Acquired Immunodeficiency Syndrome↗
PubMed1989

The transmission dynamics of the human immunodeficiency virus type 1 in the male homosexual community in the United Kingdom: the influence of changes in sexual behaviour.

This paper examines the transmission dynamics of human immune deficiency virus type 1 (HIV-1) in the male homosexual population in the U.K. via numerical studies employing a mathematical model representing the principal epidemiological process. The model is based on an assumption of proportionate mixing between different sexual-activity classes (defined by the rate of sexual partner change per unit of time) and incorporates heterogeneity in sexual activity, distributed infection and incubation periods and the recruitment of susceptibles to the sexually active population. The sensitivity of model predictions to various assumptions and parameter assignments is examined. Numerical studies of model behaviour focus on the influence of changes in the magnitudes of the transmission parameters, associated with three periods of infectiousness during the incubation period of acquired immune deficiency syndrome (AIDS), on the magnitude and duration of the epidemic and on the level of the endemic equilibrium state. Predicted temporal trends in the incidence of AIDS are shown to be particularly sensitive to changes in the intensities and durations of the stages of infectiousness. Most of the paper addresses the influence of changes in sexual behaviour on the magnitude and duration of the epidemic. Numerical simulations show that the manner in which behavioural changes occur and who is influenced by such changes (i.e. infecteds or susceptibles, the sexually active population or new recruits to this population) have a major impact on the future timecourse of the epidemic. The greatest reduction in the incidence of AIDS over the coming decades is induced by changes in the rate of sexual-partner change among the sexually active population, particularly those currently infected. The time periods at which changes in behaviour occur, in relation to the starting point of the epidemic (assumed to be 1979), are also of particular significance to the future pattern of the incidence of disease and infection. Changes in behaviour early on in the timecourse of the epidemic have a much greater impact than equivalent changes at latter time points. On the basis of limited data on the pattern of change in sexual behaviour among the male homosexual community in the U.K., numerical studies of model behaviour tentatively suggest that the epidemic is at, or near to, a period of peak incidence of the disease AIDS. Analyses suggest that, following the peak in incidence, there will be a period of slow decline over many decades provided recent changes in behaviour are maintained in the coming years.(ABSTRACT TRUNCATED AT 400 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1989

Pertussis in England and Wales: an investigation of transmission dynamics and control by mass vaccination.

The epidemiology of pertussis and its prospects for control by mass vaccination in England and Wales are investigated by analyses of longitudinal records on incidence and vaccine uptake, and horizontal data on age-stratified case reports. Mathematical models of the transmission dynamics of the infection that incorporate loss of natural and vaccine-induced immunity plus variable vaccine efficacy are developed, and their predictions compared with observed trends. Analyses of case reports reveal that the individual force of infection is age dependent, with peak transmission in the 5- to 10-year-old age class. A model incorporating this age dependency, along with partial vaccine efficacy and loss of vaccine-induced immunity, generates predicted patterns that best mirror observed trends since mass vaccination was inaugurated in 1957 in England and Wales. Model projections accurately mirror the failure of mass vaccination to increase the inter-epidemic period of the infection (three years) over that pertaining before control. The analysis suggests that this is due to the impact of partial vaccine efficacy. Projected trends do not accurately reflect the low levels of pertussis incidence reported between epidemics in the periods of high vaccine uptake. This is thought to arise from a combination of factors, including loss of natural and vaccine induced immunity, biases in case reporting (where reporting efficiency is positively associated with the incidence of pertussis), and seasonal variations in transmission. Model predictions suggest that the vaccination of 88% of each birth cohort before the age of 1 year will eliminate bacterial transmission, provided the vaccine confers lifelong protection against infection. If vaccine-induced immunity is significantly less than lifelong (or if vaccination fails to protect all its recipients) repeated cohort immunization is predicted to be necessary to eliminate transmission. Future research needs are discussed, and emphasis is placed on the need for more refined data on vaccine efficacy, the duration of natural and vaccine-induced immunity and the incidence of clinical pertussis and subclinical infections (perhaps by the development of reliable serological tests). Future mathematical models will need especially to incorporate seasonality in transmission.

England↗
PubMed1989

The influence of individual, social group and household factors on the distribution of Ascaris lumbricoides within a community and implications for control strategies.

The distribution of Ascaris lumbricoides within a community was examined at an initial mass anthelmintic treatment programme (January 1984) and following an 11-month period of reinfection (November 1984). Similar patterns of the negative binomial parameter kappa (an inverse measure of parasite aggregation) and the proportion of parasites within the most heavily infected quartile of the community were recorded at the two dates. The pattern of parasite aggregation within individuals, measured by parameter k, appears to be a stable characteristic of this host-parasite relationship. Significant variation in the intensity of infection was observed between households in the community. The number of family members living in the house strongly influenced the mean Ascaris burden and proportion of relatively heavy infections within adults and children. This finding suggests that the density of people in a house positively influences the frequency of exposure to infective stages of Ascaris, which in turn plays a major role in determining which individuals will harbour heavy infections. Positive correlations were recorded between the initial and reinfection burdens of individuals, relative to others in the community. The correlations were strongest in the youngest and oldest age groups and were more frequently significant among age-stratified groups of females, compared to males. A comparative examination of hypothetical treatment strategies suggests that for Ascaris infections in this community, targetting age groups with anthelmintic treatment would probably be more cost-effective in the long term in reducing the abundance of this parasite than selective treatment of individually identified heavy infections.

Adolescent↗
PubMed1989

Non-linear phenomena in host-parasite interactions.

The paper examines non-linear dynamical phenomena in host-parasite interactions by reference to a series of different problems ranging from the impact on transmission of control measures based on vaccination and chemotherapy, to the effects of immunological responses targeted at different stages in a parasite's life-cycle. Throughout, simple mathematical models are employed to aid in interpretation. Analyses reveal that the influence of a defined control measure on the prevalence or intensity of infection, whether vaccination or drug treatment, is non-linearly related to the magnitude of control effort (as defined by the proportion of individuals vaccinated or treated with a drug). Consideration of the relative merits of gametocyte and sporozoite vaccines against malarial parasites suggests that very high leves of cohort immunization will be required to block transmission in endemic areas, with the former type of vaccine being more effective in reducing transmission for a defined level of coverage and the latter being better with respect to a reduction in morbidity. The inclusion of genetic elements in analyses of the transmission of helminth parasites reveals complex non-linear patterns of change in the abundance of different parasite genotypes under selection pressures imposed by either the host immunological defences or the application of chemotherapeutic agents. When resistance genes are present in parasite populations, the degree to which abundance can be suppressed by chemotherapy depends critically on the frequency and intensity of application, with intermediate values of the former being optimal. A more detailed consideration of the impact of immunological defences on parasite population growth within an individual host, by reference to the erythrocytic cycle of malaria, suggests that the effectiveness of a given immunological response is inversely related to the life-expectancy of the target stage in the parasite's developmental cycle.

Animals↗
PubMed1989

Seroepidemiological study of the transmission of the mumps virus in St. Lucia, West Indies.

A seroepidemiological study of the prevalence of mumps virus specific antibodies reveals a pattern of endemic persistence on the island of St Lucia in the West Indies. In the unvaccinated population the proportion seropositive rose rapidly in the child age classes to attain a stable plateau close to unity in value in the teenage and adult age groups. The average age at infection was estimated to be between 3 and 4 years of age and the average duration of detectable levels of maternally derived antibodies was approximately 3 months. Analyses based on mathematical models of the transmission dynamics of the virus suggest that in excess of 75% of each cohort of 1- to 2-year-old children must be effectively immunized to eliminate mumps virus transmission. A mumps radial haemolysis test, developed for quantitative measurements of antibody, is discussed.

Adolescent↗