Assessment of guidelines for limiting exposures to emf using methods of probabilistic risk analysis.

Allowable limits of human exposure to radiofrequency fields commonly include a "factor of safety," typically between 10 to 50, which is somewhat arbitrary. The broad objective in our work is to assess radiofrequency exposure limits, hazard thresholds, and safety factors using methods of probabilistic risk analysis. We focus our analysis on the variables affecting peak radiofrequency specific energy absorption rate (SAR) values in the brain from digital mobile telephones operating at approximately 900 MHz. As SAR is defined as a product of positive random variables, it is not unreasonable to assume that SAR has a lognormal distribution. Our analysis of component SAR variables such as conductivity and permittivity of grey brain matter and radiated field strengths using experimental and numerical modeling data strongly supports our hypothesis that SAR values are distributed lognormally. It then follows that the probability that the SAR exceeds a certain threshold can be derived directly and is shown to be very low for handset SARs relative to presently allowable standard limits.

Blood pressure patterns and cardiovascular risk factors in rural and urban gambian communities.

Hypertension is emerging as an important public health problem in sub-Saharan Africa. We studied blood pressure (BP) patterns, hypertension and other cardiovascular risk factors in a rural and an urban area of The Gambia. A total of 5389 adults (> or =15 years) were selected by cluster sampling in the capital Banjul and a rural area around Farafenni. A questionnaire was completed, BP, pulse rate, height and weight were recorded. Glucose was measured 2 h after a 75 g glucose load among participants > or =35 years (n = 2301); total cholesterol, triglycerides, creatinine and uric acid were measured among a stratified subsample (n = 1075). A total of 7.1% of the study participants had a BP > or =160/95 mm Hg; 18.4% of them had a BP > or =140/90 mm Hg. BP was significantly higher in the urban area. BP increased with age in both sexes in both areas. Increasing age was the major independent risk factor for hypertension. Related cardiovascular risk factors (obesity, diabetes and hyperlipidaemia) were significantly more prevalent in the urban area and among hypertensives; 17% of measured hypertensives were aware of this, 73% of people who reported to have been diagnosed as hypertensive before had discontinued treatment; 56% of those who reported being on treatment were normotensive. We conclude that hypertension is no longer rare in either urban or rural Gambians. In the urban site hypertension and related cardiovascular risk factors were more prevalent. Compliance with treatment was low. Interventions aimed at modifying risk factors at the population level, and at improving control of diagnosed hypertension are essential to prevent future increases of cardiovascular morbidity and mortality. In view of limited resources and feasibility of intervention in rural Gambia, these could initially be directed towards urbanised populations.

Is there a role for glycosuria testing in sub-Saharan Africa?

BACKGROUND: With increasing urbanization and westernization, rates of diabetes in sub-Saharan Africa (sSA) are likely to rise. Early detection and intervention plays an important role in delaying development of complications. In sSA in particular there is need for an affordable, reliable, safe, feasible test to avert human suffering and exhausting already stressed health facilities. METHODS: Data from two large community-based studies were used to assess the value of glycosuria testing in the detection of diabetes in adults in a sub-Saharan country. A first study (A) tested participants for glycosuria by dipstick; if positive, fasting capillary glucose was measured. A later study (B) measured glucose concentration in venous blood 2 h after a 75-g glucose load; if glycaemia was > or = 10 mmol/l, urine was tested for glycosuria. RESULTS: The positive predictive value of glycosuria for a diagnosis of diabetes (fasting glucose > or = 6.7 mmol/l) was 48%. Sensitivity was 64% (57% if a 2-h-value > or = 10 mmol/l was used as gold standard). Sensitivity was higher among overweight and/or hypertensive subjects, among elderly people in the urban area, and among subjects with higher blood glucose levels. Extrapolated specificity was 99.7%, and the likelihood ratio 190. CONCLUSIONS: Glycosuria testing can identify a considerable number of undiagnosed diabetic patients when specially targeted at high-risk groups (obese, hypertensive, or elderly people). Dipstick glycosuria testing is an appropriate, safe, feasible test for sSA, where the prevalence of diabetes is expected to increase considerably in the near future.

Eyelid movements and mental activity at sleep onset.

The nature and time course of sleep onset (hypnagogic) mentation was studied in the home environment using the Nightcap, a reliable, cost-effective, and relatively noninvasive sleep monitor. The Nightcap, linked to a personal computer, reliably identified sleep onset according to changes in perceived sleepiness and the appearance of hypnagogic dream features. Awakenings were performed by the computer after 15 s to 5 min of sleep as defined by eyelid quiescence. Awakenings from longer periods of sleep were associated with (1) an increase in reported sleepiness, (2) a decrease in the length of mentation reports, (3) a decrease in the frequency of reports of normal, wake-like thoughts, (4) an increase in the frequency of "unusual thoughts," and (5) increased frequencies of formal dream features, including visual hallucination, self-representation, fictive movement, narrative plot, and bizarreness. While sleep-onset reports can include all features of rapid eye movement (REM) dream reports, the number of such features is markedly reduced at sleep onset, suggesting that this mentation is a greatly diminished version of REM dreaming.

Global prevalence and incidence estimates of selected curable STDs.

OBJECTIVES: To update the WHO global and regional estimates of the prevalence and incidence of syphilis, gonorrhoea, chlamydia, and trichomoniasis. METHODS: Prevalence estimates for syphilis, gonorrhoea, chlamydia, and trichomoniasis were generated for each of the nine UN regions for males and females between the ages of 15 and 49 in 1995 based on an extensive review of the published and unpublished medical literature since 1985. Incidence estimates were based on the prevalence figures and adjusted to take into account the estimated average duration of infection for each disease in a particular region. The latter was assumed to depend upon a number of factors including the duration of infection in the absence of treatment, the proportion of individuals who develop symptoms, the proportion of individuals treated, and the appropriateness of treatment. RESULTS: In 1995 there were over 333 million cases of the four major curable STDs in adults between the ages of 15 and 49--12 million cases of syphilis, 62 million cases of gonorrhoea, 89 million cases of chlamydia, and 170 million cases of trichomoniasis. Geographically, the vast majority of these cases were in the developing world reflecting the global population distribution. CONCLUSIONS: STDs are among the most common causes of illness in the world. Estimates of the global prevalence and incidence of these infections are limited by quantity and quality of data available from the different regions of the world. Improving global STD estimates will require more well designed epidemiological studies on the prevalence and duration of infection.

Modeling the impact and cost-effectiveness of HIV prevention efforts.

OBJECTIVES: This study explores how mathematical models can be used to examine the relationship between the effectiveness and costs of different prevention strategies. The analysis, based on a model designed to simulate the spread of HIV in sub-Saharan Africa, illustrates how the impact and relative cost-effectiveness of a prevention programme are sensitive to a number of factors including the rate of spread of HIV prior to the introduction of the programme, the measure used to evaluate the impact of the programme, and the point when the programme is introduced in the epidemic. RESULTS: Assessing the impact and cost-effectiveness of different HIV prevention strategies is problematic. Not only are there difficulties in collecting the relevant data, but the impact of a prevention programme may be highly non-linear in character because of the many factors that determine the net rate of viral transmission. The long incubation period of HIV further complicates the analysis as the benefits from preventing a case of infection extend over a number of years. CONCLUSIONS: The results highlight the need to collect more data on the impact and costs of prevention programmes if we are to ensure that the available resources for HIV prevention are to be used both efficiently and equitably.

Age-dependent choice of sexual partners and the transmission dynamics of HIV in Sub-Saharan Africa.

A mathematical model of the transmission of HIV-1 within heterosexual populations in Sub-Saharan Africa is described and its properties analysed. The model incorporates epidemiological and demographic processes and extends previous work in this area via the inclusion of age and sex dependency in rates of sexual partner change, and sexual partner choice dependent on age. Parameter assignments are made on the basis of current data on the transmission dynamics of HIV-1 and the demography of human populations in Africa. Both age-dependent rates of sexual activity and the sexual contact of males with females younger than themselves act to enhance the predicted demographic impact. With realistic parameter values, the model suggests AIDS is able to reverse the sign of population growth rates from positive to negative values over a timescale of a few decades. The sensitivity of this prediction is examined in relation to changes in the pattern of sexual contact between different age classes of females and males, different patterns of change in the age-dependent rate of sexual partner change, different assumptions concerning the doubling time of the epidemic in its early stages, and the relative efficiencies of viral transmission between men and women, and vice versa. The impact AIDS is predicted to have on the number of young and elderly persons as a fraction of the number of productive adults (the dependancy ratio) is examined under various assumptions concerning the weighting to be applied to mirror the burden imposed by the care of those with AIDS. The paper includes an assessment of the influence of the timing of changes in sexual behaviour, or the promotion of the use of condoms, on the predicted course of the epidemic. The paper concludes with a discussion of data needs and the model refinements required to more accurately mirror current understanding of the epidemiology of HIV-1.

PIP: This paper describes and analyzes a mathematical model of HIV-1 transmission in heterosexual populations of sub-Saharan Africa. The model includes both epidemiological and demographic processes. It extends work previously performed in the field by including age and sex dependency in the rates of sexual partner change and sexual partner choice dependent on age. The model demonstrates how age-dependent rates of sexual activity and male sexual contact with younger females enhances the predicted demographic impact. Over a few decades, and with realistic parameters, the model suggests that AIDS may feasibly reduce population growth from current positive to negative rates. The model is tested under different variable and assumptions to evaluate the sensitivity of predictions. Additional data and model refinements needed for future research are mentioned.

The spread of HIV-1 in Africa: sexual contact patterns and the predicted demographic impact of AIDS.

The spread of HIV-1 in Africa is examined here in the light of recent information on the main epidemiological and behavioural determinants of transmission. Mathematical models incorporating demographic, epidemiological and behavioural processes are used to assess the potential demographic impact of the disease AIDS. These analyses highlight the significance of patterns of sexual behaviour, and in particular networks of sexual contact, on the predicted spread of infection. Current data reveal substantial variations in the degree of spread between and in countries, but new analyses support earlier predictions that in the worst-afflicted areas AIDS is likely to change population growth rates from positive to negative values in a few decades.

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.

PIP: A previously published mathematical model of the transmission of dynamics of HIV is used to simulate the demographic and economic consequences of introducing various degrees of control measures to reduce heterosexual transmission of HIV in sub-Sahara Africa. The model is fully age-structured and its output is projection over time (100 years) of total population size, broken down by age and sex, and numbers with HIV or AIDS. The doubling time of the epidemic is set at 1.5 years; the mean incubation period for AIDS 8 years for adults and 2 years for children; life expectancy of infected persons is set at 1 year; probability of heterosexual transmission 10% per partner contact; that of vertical transmission 50%. The factor beta c, or average rate at which an infected person infects others, varies with level of control introduced. For a population of 16.6 million multiplying at 3.8% per year, with AIDS and no controls, growth rates will begin to decline at year 30, to reach 8.6 million by year 100. Without AIDS, it would have reached 740 million. With AIDS, the structure of the population would change to a higher proportion under 15 and over 25, but lower proportion between 15-25 years. Economically, assuming a GNP of $300 per capita, and an expenditure of $100 per AIDS patient, by year 50 2.4% of the GNP would be spent treating AIDS victims. Figures are also estimated for a fixed or falling GNP, such that funds to spend on AIDS treatment per person would fall over time. If control measures were taken, savings in treatment costs would be substantial, as much as $2.4 billion if transmission were reduced 75% over 25 years. If was noted that sub- Sahara African countries simply do not have funds to pay for Western style treatment of AIDS patients. The cost of the drug zidovudine (AZT) for 1 person is more than that of 1 community health center for a year. Already half the hospital beds are taken up by AIDS patient in some urban areas.

Tetrahydrocannabinol inhibits adenyl cyclase in human leukemia cells.

Delta 9-tetrahydrocannabinol has been shown to induce incomplete maturation in ML2 human leukemia cell lines. We extend the observation of its induction of morphologic maturation to HL60 cells and of its induction of growth restriction to HL60 and K562 cells. We show that tetrahydrocannabinol reduces the cyclic AMP content of ML2 cells. Finally we demonstrate that this agent inhibits adenyl cyclase activity in ML2 cell membrane-enriched fractions. This finding in myeloid cells is compatible with one hypothesis of cannabinoid action in neuronal cells.