Coverage Threshold Research Articles

Preventing Childhood Malaria in Africa by Protecting Adults from Mosquitoes with Insecticide-Treated Nets

BackgroundMalaria prevention in Africa merits particular attention as the world strives toward a better life for the poorest. Insecticide-treated nets (ITNs) represent a practical means to prevent malaria in Africa, so scaling up coverage to at least 80% of young children and pregnant women by 2010 is integral to the Millennium Development Goals (MDG). Targeting individual protection to vulnerable groups is an accepted priority, but community-level impacts of broader population coverage are largely ignored even though they may be just as important. We therefore estimated coverage thresholds for entire populations at which individual- and community-level protection are equivalent, representing rational targets for ITN coverage beyond vulnerable groups.Methods and FindingsUsing field-parameterized malaria transmission models, we show that high (80% use) but exclusively targeted coverage of young children and pregnant women (representing <20% of the population) will deliver limited protection and equity for these vulnerable groups. In contrast, relatively modest coverage (35%–65% use, with this threshold depending on ecological scenario and net quality) of all adults and children, rather than just vulnerable groups, can achieve equitable community-wide benefits equivalent to or greater than personal protection.ConclusionsCoverage of entire populations will be required to accomplish large reductions of the malaria burden in Africa. While coverage of vulnerable groups should still be prioritized, the equitable and communal benefits of wide-scale ITN use by older children and adults should be explicitly promoted and evaluated by national malaria control programmes. ITN use by the majority of entire populations could protect all children in such communities, even those not actually covered by achieving existing personal protection targets of the MDG, Roll Back Malaria Partnership, or the US President's Malaria Initiative.

Model Projections on the Required Coverage of Syringe Distribution to Prevent HIV Epidemics Among Injecting Drug Users

Although syringe distribution is effective in preventing HIV transmission among injecting drug users (IDUs), there is little evidence on the required coverage to substantially reduce HIV transmission. A mathematical model is developed to explore the relationship between the endemic HIV prevalence among IDUs and the coverage of syringe distribution. Data from IDU populations in the United Kingdom and Belarus are used to explore the implications of increasing coverage and the effect of changes in other behaviors. Projections suggest that there is a coverage threshold, which, if reached, could lead to substantial decreases in HIV prevalence. The threshold largely depends on the frequency that IDUs inject and (safely) reuse their syringes, and corresponds to less than 4 syringe-sharing events per IDU per month. Other factors, such as the injecting cessation rate and efficacy of syringe cleaning, only have substantial impact near threshold coverage levels. Our results support a policy of increasing the coverage of syringe distribution but highlight the difficulty in producing a universal coverage target. Great public health benefit could be conferred by encouraging the safe reuse of an IDU's own syringes and small stable injecting groups. Policies that discourage this will negate the impact of syringe distribution interventions.

The Small Firm Exemption and the Single Employer Doctrine in Employment Discrimination Law

The small firm exemption is a provision of Title VII and the other major federal employment discrimination laws that exempts very small firms from coverage as employers. Under the Title VII version of the exemption, for example, an employer is exempt as long as it employs no more than fourteen employees. However, a small firm might be affiliated or integrated with other firms, which collectively employ more than the number of employees required for coverage. The single employer doctrine is a rule for treating affiliated but separately organized firms as if they were one employer, for purposes of meeting the statutory threshold for coverage. Lately, a number of critics lead by Judge Posner have questioned the doctrine's place in discrimination law. The critics charge that the collective bargaining cases in which the doctrine first evolved are not valid precedents for the doctrine's use as a rule of coverage in discrimination cases, and that the doctrine defeats the purposes of the small firm exemption. Judge Posner and other critics would treat affiliated but separately organized firms as a single employer only if it would be appropriate to pierce the corporate veil or hold the firms jointly liable under traditional rules of corporate law. In this article I explore the origins of the single employer doctrine and its vivid presence in the background of the Congressional debates leading to the small firm exemption. I also find support for the doctrine in the text of Title VII, and I show that the doctrine is not only consistent with the purpose of the small firm exemption but is necessary to fully achieve the exemption's purpose.

Vaccination coverage survey versus administrative data in the assessment of mass yellow fever immunization in internally displaced persons—Liberia, 2004

Yellow fever (YF) is a mosquito-borne vaccine-preventable disease with high mortality. In West Africa, low population immunity increases the risk of epidemic transmission. A cluster survey was conducted to determine the effectiveness of a mass immunization campaign using 17D YF vaccine in internally displaced person (IDP) camps following a reported outbreak of YF in Liberia in February 2004. Administrative data of vaccination coverage were reviewed. A cluster sample size was determined among 17,384 shelters using an 80% vaccination coverage threshold. A questionnaire eliciting demographic information, household size, and vaccination status was distributed to randomly selected IDPs. Data were analyzed to compare vaccination coverage rates of administrative versus survey data. Among 87,000 persons estimated living in IDP camps, administrative data recorded 49,395 (57%) YF vaccinated persons. A total of 237 IDPs were surveyed. Of survey respondents, 215 (91.9%, 95% CI 88.4–95.4) reported being vaccinated during the campaign and 196 (83.5%, 95% CI 78.6–88.5) possessed a valid campaign vaccination card. The median number of IDPs living in a shelter was 4 (range, 1–8) and 69,536 persons overall were estimated to be living in IDP camps. Coverage rates from a rapid survey exceeded 90% by self-report and 80% by evidence of a vaccination card, indicating that the YF immunization campaign was effective. Survey results suggested that administrative data overestimated the camp population by at least 20%. An emergency, mop-up vaccination campaign was avoided. Coverage surveys can be vital in the evaluation of emergency vaccination campaigns by influencing both imminent and future immunization strategies.

Acetylene Coupling on Cu(111): Formation of Butadiene, Benzene, and Cyclooctatetraene

Acetylene trimerizes to benzene on the (111) face of copper, as it does on the (100) and (110) planes. However, Cu(111) also yields butadiene and cyclooctatetraene, the latter never previously found with Cu or any other material. No coverage threshold is observed for the onset of these coupling reactions, implying high adsorbate mobility: gaseous benzene is formed by a surface reaction rate-limited process, whereas butadiene and cyclooctatetraene are formed by desorption rate-limited processes. H/D isotope tracing shows that benzene formation proceeds via a statistically random associative mechanism, whereas butadiene formation is associated with strong kinetic isotope effects, probably associated with C-H cleavage. A pericyclic mechanism involving dimerization of C4H4 metallocycles is proposed to account for the formation of cyclooctatetraene. We also found that approximately 45 nm alpha-alumina supported copper particles operated under catalytic conditions at atmospheric pressure yield the same principal reaction products as those found with Cu(111) under vacuum conditions. It therefore seems likely that the elementary reaction steps that describe the surface chemistry of the model system are also important under practical conditions. Comparison of the structure, bonding, and reactivity of acetylene on Cu(111) and Pd(111) indicates that the effectiveness of copper in promoting C-H cleavage in adsorbed acetylene is associated with greater rehybridization of the C-C bond with concomitant weakening of the C-H bond.

A qualitative study of a vaccination model with non-linear incidence

We propose a new deterministic model for the dynamics of an infectious disease in the presence of a preventive (prophylactic) vaccine and an effective therapeutic treatment. The three-dimensional model, which assumes a non-linear incidence rate, is analysed qualitatively to determine the stability of its equilibria. The optimal vaccine coverage threshold needed for disease control and eradication is determined analytically (and verified using numerical simulations). The case where no vaccination is given (vaccination-free model) is also investigated. Using a Dulac function, it is shown that the vaccination-free model has no limit cycles.

Predicting the effect of the Oregon Health Plan on Medicaid coverage for outpatients with HIV.

The Oregon Health Plan, which took effect in February 1994, extends Medicaid eligibility but limits coverage to conditions and treatments above a certain threshold on a prioritized list. Retrospective analysis was conducted on records of visits to two Oregon human immunodeficiency virus (HIV) outpatient clinics in 1991 and 1992 to determine Medicaid coverage if the plan had been operational. Of 1129 patients, 21.1% were Medicaid-eligible; an additional 56.5% would have been eligible under the Oregon plan. Only 5.0% to 6.8% of these patients' visits were for conditions listed below the plan's coverage threshold; almost none of these were for HIV-specific conditions.

Moral Hazard Cycles in Individual‐Coverage Crop Insurance

AbstractThis paper examines the moral hazard implications of individual‐coverage crop insurance contracts. Individual‐coverage contracts are informationally superior to standard contracts because the farmer's coverage is proportional to his average historical yield. Despite this apparent benefit, the steady‐state solution is shown to be characterized by moral hazard cycles, where moral hazard is practiced in alternative periods. The amplitude of the cycle and, thus, the variability in planned production is shown to be larger the lower the degree of production uncertainty, the fewer the number of years used in the averaging process, the higher the coverage threshold, and the lower the level of co‐insurance.

Submonolayer Na coverage threshold for water vapour adsorption on Cu (111)/Na

When Na-covered Cu(111) is exposed to water vapour the adsorption proceeds rapidly only if the amount of Na on the surface is greater tha 10% of full monolayer coverage. The adsorption is monitored via the electron energy loss spectrum which for the coadsorption system shows vibrational excitations at 18 and 36 meV while for Na on Cu (111) the adsorbate vibrations perpendicular to the surface produce a loss peak at 21 meV.

Electron yield from an alkali submonolayer: Li/Be(0001)

Total and partial electron yield spectra at the Li 1s threshold for a subsaturation coverage of Li/Be(0001) are presented. Our goal is to understand the electronic properties of a metal as a function of its dimensionality, which for two‐dimensional films also involves understanding the role of the substrate chosen, including background contributions in overlayer core spectra. We discuss a method which we have found effective in analyzing the yield data.

Lepton pairs from heavy quarks produced in hadron colliders.

Distributions with respect to rapidity and transverse momenta are studied for lepton pairs arising from decays of heavy quarks produced in hadron-hadron colliders. Particular attention is paid to the merits of complete angular coverage and low threshold in transverse momentum.

Structure and electrical conduction of discontinuous gold films evaporated in vacuum on carbon and silicon monoxide substrates

Abstract Experimental results concerning the structure and d.c. electrical conductance of discontinuous gold films evaporated in vacuum (1×10-7 Torr) on amorphous carbon and SiO substrates are reported. It is shown that the distribution of gold islands can be described by a log-normal distribution with d =10–73 nm and σ=1.22–1.59. For the “maze” structure the “break-up” effect was observed at about 360 K for Au/C films and at about 320 K for Au/SiO films. We observed a high threshold (about 0.85) of metal surface coverage to be necessary for the transition from activated to metallic conduction in the film. A discussion of the observed effects and of discrepancies between experimental data and relevant current theories is given.