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Biomedical subjects

R W Snow

Publications and source records attributed to R W Snow.

At least 37 records · Page 2Linked to original sources
PubMed2002

A comparative cost analysis of insecticide-treated nets and indoor residual spraying in highland Kenya.

The relative cost of indoor residual house-spraying (IRS) versus insecticide-treated bednets (ITNs) forms part of decisions regarding selective malaria prevention. This paper presents a cost comparison of these two approaches as recently implemented by Merlin, a UK emergency relief organization funded through international donor support and working in the highland districts of Gucha and Kisii in Kenya. The financial costs (cash expenditures) and the economic costs (including the opportunity costs of using existing staff and volunteers, and an annualized cost for capital items) were assessed. The financial cost for IRS was US dollars 0.86 per person protected, compared with 4.21 dollars for ITNs (reducing to 3.42 dollars to the provider assuming cost recovery). The economic cost per person protected for IRS was 0.88 dollars, compared with 2.34 dollars for ITNs. The costs for ITNs were sensitive to the number of nets sold per community group ('efficiency'), as the delivery costs constituted upwards of 40% of the total cost. However, even marked increases in efficiency of these groups could not reduce the costs of ITNs to that comparable with IRS, except if more than one cycle of IRS was needed. The implications of predicted reductions in the cost of insecticide for both IRS and ITNs are also explored. The provision of itemized cost data allows predictions to be made on changes in the design of these programmes. Under almost all design scenarios, IRS would appear to be a more cost-efficient means of vector control in the Kenyan highlands.

Bedding and Linens↗
PubMed2002

Intra-household relations and treatment decision-making for childhood illness: a Kenyan case study.

This study, conducted on the Kenyan coast, assesses the effect of intra-household relations on maternal treatment-seeking. Rural and urban Mijikenda mothers' responses to childhood fevers in the last 2 weeks (n=317), and to childhood convulsions in the previous year (n=43), were documented through survey work. The intra-household relations and decision-making dynamics surrounding maternal responses were explored through in-depth individual and group interviews, primarily with women (n=223). Responses to convulsions were more likely than responses to fevers to include a healer consultation (p<0.0001), and less likely to include the purchase of over-the-counter medications (p<0.0001). Mothers received financial or advisory assistance from others in 71% (n=236) of actions taken outside the household in response to fevers. In-depth interviews suggested that general agreement on appropriate therapy results in relatively few intra-household conflicts over the treatment of fevers. Disputes over perceived cause and appropriate therapy of convulsions, however, highlighted the importance of age, gender and relationship to household head in intra-household relations and treatment decision-making. Although mothers' treatment-seeking preferences are often circumscribed by these relations, a number of strategies can be drawn upon to circumvent 'inappropriate' decisions, sometimes with implications for future household responses to similar syndromes. The findings highlight the complexity of intra-household relations and treatment decision-making dynamics. Tentative implications for interventions aimed at improving the home management of malaria, and for further research, are presented.

Adaptation, Psychological↗
PubMed2001

Malaria early warning in Kenya.

Kenya displays large spatiotemporal diversity in its climate and ecology. It follows that malaria transmission will reflect this environmental heterogeneity in both space and time. In this article, we discuss how such heterogeneity, and its epidemiological consequences, should be considered in the development of early warning systems for malaria epidemics.

Disease Outbreaks↗
PubMed2001

The past, present and future of childhood malaria mortality in Africa.

During the past few years, there has been a historic series of declarations of renewed commitment to malaria control in Africa. Whether the burden of malaria is increasing in Africa is a moot point. This article attempts to re-construct the evidence for the trends in childhood mortality as a result of Plasmodium falciparum infection over the last century in Africa.

Africa↗
PubMed2001

Relationships between drinking problems and drinking locations among convicted drinking drivers.

This study examines relationships between drinking problems and the frequency of drinking in eight types of places within a sample of convicted drinking drivers. Drinking problems were measured by two instruments, the Mortimer-Filkins Questionnaire (MFQ) and the Alcohol Use Disorders Identification Test (AUDIT) Core Questionnaire. Data were collected from convicted drinking drivers who were ordered by the court to attend the Mississippi Alcohol Safety Education Program (MASEP). Both the MFQ and the AUDIT were found to be more strongly related to the frequency of drinking in moving automobiles than to the frequency of drinking in any other type of place. This suggests that drinking drivers with severe drinking problems are more likely to drink in moving automobiles than are those with less severe problems. The strong linkage between severe alcohol problems and drinking in automobiles has important implications with respect to highway safety.

Adult↗
PubMed2000

Etiology of interepidemic periods of mosquito-borne disease.

Dengue viruses and malaria protozoa are of increasing global concern in public health. The diseases caused by these pathogens often show regular seasonal patterns in incidence because of the sensitivity of their mosquito vectors to climate. Between years in endemic areas, however, there can be further significant variation in case numbers for which public health systems are generally unprepared. There is an acute need for reliable predictions of within-year and between-year epidemic events. The prerequisite for developing any system of early warning is a detailed understanding of the factors involved in epidemic genesis. In this report we discuss the potential causes of the interepidemic periods in dengue hemorrhagic fever in Bangkok and of Plasmodium falciparum malaria in a highland area of western Kenya. The alternative causes are distinguished by a retrospective analysis of two unique and contemporaneous 33-year time series of epidemiological and associated meteorological data recorded at these two sites. We conclude that intrinsic population dynamics offer the most parsimonious explanation for the observed interepidemic periods of disease in these locations.

Animals↗
PubMed2000

Earth observation, geographic information systems and Plasmodium falciparum malaria in sub-Saharan Africa.

This review highlights the progress and current status of remote sensing (RS) and geographical information systems (GIS) as currently applied to the problem of Plasmodium falciparum malaria in sub-Saharan Africa (SSA). The burden of P. falciparum malaria in SSA is first summarized and then contrasted with the paucity of accurate and recent information on the nature and extent of the disease. This provides perspective on both the global importance of the pathogen and the potential for contribution of RS and GIS techniques. The ecology of P. falciparum malaria and its major anopheline vectors in SSA in then outlined, to provide the epidemiological background for considering disease transmission processes and their environmental correlates. Because RS and GIS are recent techniques in epidemiology, all mosquito-borne diseases are considered in this review in order to convey the range of ideas, insights and innovation provided. To conclude, the impact of these initial studies is assessed and suggestions provided on how these advances could be best used for malaria control in an appropriate and sustainable manner, with key areas for future research highlighted.

Africa South of the Sahara↗
PubMed2000

Comparing the predictive validity of DUI risk screening instruments: development of validation standards.

AIMS: This study compares the predictive efficacy of driving under the influence (DUI) screening instruments validated in previous studies, illustrates how variations in base rates of failure and selection ratios affect conclusions concerning the efficacy of different instruments, and develops evaluation standards to ensure valid comparisons of risk prediction instruments. DESIGN: The study: (1) examines a sample of 4815 DUI offenders to illustrate how variations in base rates of failure and selection ratios affect traditional measures of predictive efficacy, (2) uses such measures to compare the predictive efficacy of 10 instruments validated in previous studies, and (3) demonstrates the use of a measure of predictive efficacy which is relatively insensitive to the aforementioned variations. FINDINGS: While three instruments examined at specific cut-points consistently ranked highest on several measures of predictive efficacy, use of different evaluation standards produced substantively different conclusions regarding the efficacy of different instruments. Based on the analyses, standards for validation of risk prediction instruments were developed. CONCLUSIONS: The findings illustrate how failure to use equivalent standards have led to erroneous conclusions concerning the relative predictive efficacy of different risk prediction instruments. The standards developed in this study should facilitate equivalent comparisons of the predictive efficacy of risk prediction instruments.

Alcohol Drinking↗
PubMed2000

Paediatric survival and re-admission risks following hospitalization on the Kenyan coast.

The district general hospital (DGH) is a common feature of health service provision in many developing countries. We have used linked demographic and clinical surveillance in a rural community located close to a DGH on the Kenyan coast to define the use and public health significance of essential clinical services provided by it. Of a birth cohort of over 4000 children followed for approximately 6 years, about a third were admitted to hospital at least once. Significantly more children admitted with major infectious diseases such as malaria and acute respiratory tract infections were readmitted with the same condition during the surveillance period than would have been expected by chance. Among surviving admissions, mortality post-discharge was significantly higher than in the cohort which had not been admitted within 3, 6 and 12 months. Most of the patients who died after discharge had been admitted with a diagnosis of gastroenteritis. Most children admitted to the DGH survive hospitalization and the remaining period of childhood. Despite no clinical trial evidence to support the claim, it seems reasonable to assume that in the absence of intensive clinical management provided by a DGH, a significant proportion of these children would not have survived. However, the DGH is able to define a group of at-risk children who re-present with severe complications of infectious disease, and of these several may have underlying conditions not amenable to DGH intervention and continue to have a poor prognosis. Both groups of children represent statistically significant subsets of a rural paediatric community and the future organization and co-ordination of DGH and primary care services need to work in unison to strengthen the service needs of children at risk.

Child↗
PubMed2000

Using evidence to change antimalarial drug policy in Kenya.

Chloroquine resistance was first detected in Kenya in 1978 and escalated during the 1980s. Chloroquine remained the treatment of choice for uncomplicated malaria infections until revised guidelines were launched in 1998 despite a plethora of scientific evidence on failure. This review analyses the range and quality of the evidence base that was used to change the drug policy in Kenya from chloroquine to SP and examines the process of consensus building and decision making. Our review illustrates the difficulties in translating sensitivity data with gross geographical, temporal and methodological variations into national treatment policy. The process was complicated by limited options, unknown adverse effects of replacement therapies, cost, as well as limited guidance on factors pertinent to changing the drug policy for malaria. Although > 50% of the studies showed parasitological failures by 1995, there was a general lack of consensus on the principles for assessing drug failures, the inclusion criteria for the study subjects and the relative benefits of parasitological and clinical assessments. A change in international recommendations for assessment of drug efficacy in 1996 from parasitological to clinical response further perplexed the decisions. There is an urgent need for international standards and evidence-based guidelines to provide a framework to assist the process by which decision-makers in malaria-endemic countries can make rational choices for antimalarial drug policy change.

Antimalarials↗
PubMed2000

Malaria control in East Africa: the Kampala Conference and the Pare-Taveta Scheme: a meeting of common and high ground.

The 1950 Malaria Conference in Equatorial Africa, held in Kampala, Uganda, has been remembered primarily for its decision to control malaria '...by modern methods as soon as feasible, whatever the original degree of endemicity, and without awaiting the outcome of further experiments.' This decision was far from conclusive and, indeed, reflects only one side of the argument which brought two groups of malariologists into direct opposition on the wisdom of malaria control in equatorial Africa, using modern methods such as DDT. Through an examination of the unpublished verbatim transcript of the Kampala Conference, we are able to document the 'furious debates' which took place at Kampala in 1950. We highlight, in particular, the adamant concerns expressed by some of the delegates that intervention in areas of high malaria transmission might lead to a loss of naturally acquired immunity which, in turn, could give rise to a resurgence of malaria, should the control strategies fail to be sustained. As we show, this concern had been expressed by a number of malariologists working in East Africa in the first half of the twentieth century, but it was only with the advent of DDT, as a residual insecticide, that the implications of wide-spread control, in the absence of any knowledge of the long-term consequences, became a serious possibility. While the Kampala Conference gave the 'go ahead' to control malaria in Africa without awaiting the outcome of 'further experiments', a number of participants insisted that a field trial should be set up to evaluate the impact of malaria on areas of high transmission both before and after spraying: to this end, a field trial in Pare-Taveta was carried out in 1954-59. In this paper we look at the Kampala Conference for its scientific debates and the Pare-Taveta Scheme for its field applications. In the final part of the paper, we address a number of questions raised at Kampala which have, once more, become contentious issues, following the recent successful trials of ITBNs. We believe that an understanding of the historical foundations of these issues should provide an important component of the new WHO campaign to Roll Back Malaria.

Adult↗
PubMed1999

Malaria epidemiology and economics: the effect of delayed immune acquisition on the cost-effectiveness of insecticide-treated bednets.

An understanding of the epidemiology of a disease is central in evaluating the health impact and cost-effectiveness of control interventions. The epidemiology of life-threatening malaria is receiving renewed interest, with concerns that the implementation of preventive measures such as insecticide-treated bednets (ITNs) while protecting young children might in fact increase the risks of mortality and morbidity in older ages by delaying the acquisition of functional immunity. This paper aims to illustrate how a combined approach of epidemiology and economics can be used to (i) explore the long-term impact of changes in epidemiological profiles, and (ii) identify those variables that are critical in determining whether an intervention will be an efficient use of resources. The key parameters for determining effectiveness are the protective efficacy of ITNs (reduction in all-cause mortality), the malaria attributable mortality and the increased malaria-specific mortality risk due to delays in the acquisition of functional immunity. In particular, the analysis demonstrates that delayed immune acquisition is not a problem per se, but that the critical issue is whether it occurs immediately following the implementation of an ITN programme or whether it builds up slowly over time. In the 'worst case' scenario where ITNs immediately increase malaria-specific mortality due to reduced immunity, the intervention might actually cost lives. In other words, it might be better to not use ITNs. On the other hand, if reduced immunity takes two years to develop, ITNs would still fall into the category of excellent value for money compared to other health interventions, saving a year of life (YLL) at a cost of between US$25-30. These types of calculations are important in identifying the parameters which field researchers should be seeking to measure to address the important question of the net impact of delaying the acquisition of immunity through preventive control measures.

Adolescent↗
PubMed1999

Acquired immunity and postnatal clinical protection in childhood cerebral malaria.

By analysing data on the age distribution of cerebral malaria among sites of different transmission intensities, we conclude that the most plausible explanation for the epidemiological patterns seen is that (i) cerebral malaria is caused by a distinct set of Plasmodium falciparum antigenic types; (ii) these antigenic types or 'CM strains' are very common and induce strong strain-specific immunity; and (iii) the postnatal period of protection against cerebral malaria is much longer than the period of protection against other forms of severe disease. The alternative hypothesis that cerebral malaria may be caused by any 'strain' of P. falciparum is compatible with the data only if a single exposure is sufficient to protect against further episodes. This is not consistent with observations on the history of exposure of patients with cerebral malaria. Finally, it is clear that although the delayed peak in incidence of cerebral malaria (with age) can be generated by assuming that subsequent exposures carry a higher risk of disease, such an explanation is not compatible with the observation that severe disease rates are low among infants and young children in areas of high transmissibility.

Africa South of the Sahara↗
PubMed1999

A preliminary continental risk map for malaria mortality among African children.

Approaches to global public health are increasingly driven by an understanding of regional patterns of disease-specific mortality and disability. Current estimates of disease risks associated with Plasmodium falciparum in sub-Saharan Africa remain poorly defined. Through the integration of high-resolution population and climate probability models of P. falciparum transmission, geographical information systems have been used to define the spatial limits of populations exposed to the risk of infection in Africa. These estimates were combined with a range of annual malaria-specific mortality rates, derived from a variety of epidemiological approaches, among children aged 0-4 years. The best estimates of malaria-attributable mortality using this approach ranged between 0. 43 million and 0.68 million deaths per annum among an exposed population of approximately 66 million children in 1990. Despite the limitations of modelled transmission and population distributions, these empirical approaches to probabilities of infection risk and epidemiological data on mortality provide a novel approach to present and projected burdens of malaria mortality, as discussed here by Bob Snow, Marlies Craig, Uwe Deichmann and Dave le Sueur.

Africa South of the Sahara↗
PubMed1999

A climate-based distribution model of malaria transmission in sub-Saharan Africa.

Malaria remains the single largest threat to child survival in sub-Saharan Africa and warrants long-term investment for control. Previous malaria distribution maps have been vague and arbitrary. Marlies Craig, Bob Snow and David le Sueur here describe a simple numerical approach to defining distribution of malaria transmission, based upon biological constraints of climate on parasite and vector development. The model compared well with contemporary field data and historical 'expert opinion' maps, excepting small-scale ecological anomalies. The model provides a numerical basis for further refinement and prediction of the impact of climate change on transmission. Together with population, morbidity and mortality data, the model provides a fundamental tool for strategic control of malaria.

Africa South of the Sahara↗