(25/276) The impact of HIV epidemic phases on the effectiveness of core group interventions: insights from mathematical models.

Mathematical models have highlighted the disproportionate contribution of core group transmitters to the spread of sexually transmitted diseases. Because the effectiveness of interventions varies with time, it has been suggested that epidemic phases should be considered in the design of prevention strategies. This study aimed to examine the impact of HIV epidemic phases on the effectiveness of HIV interventions based on gonorrhoea screening and condom use, targeted to core groups. The results are based on a mathematical model of gonorrhoea and HIV transmission in a relatively slow spreading HIV epidemic using Cotonou (Benin) as an example. For epidemics with a low reproductive potential modest core group interventions can significantly reduce HIV incidence and prevalence. As the epidemic matures, effective interventions should also incorporate core and non-core populations. For epidemics with a high reproductive potential, core group interventions are necessary but not sufficient to have a rapid and large scale impact. A more general population approach is also needed early in the epidemic. Epidemic phases are also important in the evaluation of prevention strategies.  (+info)

(26/276) Identifying West Nile virus risk areas: the Dynamic Continuous-Area Space-Time system.

The Dynamic Continuous-Area Space-Time (DYCAST) system was developed to identify and prospectively monitor high-risk areas for West Nile virus in New York, New York (New York City). The system is based on a geographic model that uses a localized Knox test to capture the nonrandom space-time interaction of dead birds, as an indicator of an intense West Nile virus amplification cycle, within a 1.5-mile (2.41-km) buffer area and 21-day moving window. The Knox analysis is implemented as an interpolation function to create a surface of probabilities over a grid of 1,400 cells overlaying New York City. The model's parameters were calibrated using year 2000 data and information on the vector-host transmission cycle. The DYCAST system was implemented in a geographic information system and used operationally in year 2001. It successfully identified areas of high risk for human West Nile virus infection in areas where five of seven human cases resided, at least 13 days prior to the onset of illness, and proved that it can be used as an effective tool for targeting remediation and control efforts.  (+info)

(27/276) Spatial clustering of amyotrophic lateral sclerosis in Finland at place of birth and place of death.

Previous evidence for spatial clustering of amyotrophic lateral sclerosis is inconclusive. Studies that have identified apparent clusters have often been based on a small number of cases, which means the results may have occurred by chance processes. Also, most studies have used the geographic location at the time of death as the basis for cluster detection, rather than exploring clusters at other points in the life cycle. In this study, the authors examine 1,000 cases of amyotrophic lateral sclerosis distributed throughout Finland who died between June 1985 and December 1995. Using a spatial-scan statistic, the authors examine whether there are significant clusters of the disease at both time of birth and time of death. Two significant, neighboring clusters were identified in southeast and south-central Finland at the time of death. A single significant cluster was identified in southeast Finland at the time of birth, closely matching one of the clusters identified at the time of death. These results are based on a large sample of cases, and they provide convincing evidence of spatial clustering of this condition. The results demonstrate also that, if the cluster analysis is conducted at different stages of the cases' life cycle, different conclusions about where potential risk factors may exist might result.  (+info)

(28/276) A different kind of contextual effect: geographical clustering of cocaine incidence in the USA.

STUDY OBJECTIVE: Outline the use of the pairwise odds ratio (PWOR) to quantify the extent to which a binary outcome clusters geographically. Quantify the extent to which first experience with cocaine is spatially correlated within US neighbourhoods and cities. Quantify geographical clustering of first experience with cocaine by neighbourhood context. DESIGN: Estimate the PWOR of incident cocaine experience at two levels (neighbourhood, city) and compare across years. Within years, estimate the PWOR by neighbourhood disadvantage and test for trend. SETTING: US National Household Survey on Drug Abuse. PARTICIPANTS: Civilian, non-institutionalised household residents of the United States age 12 years and older interviewed in person during 1979, 1988, 1990, 1991, 1992, 1993. MAIN RESULTS: First experience with cocaine clusters within US neighbourhoods and cities. There is some evidence that the spatial correlation of first experience with cocaine increases with percentage of neighbourhood households living in poverty. CONCLUSIONS: The gradient in spatial correlation of incident cocaine experience by neighbourhood poverty level is consistent with current theories of concentrated disadvantage. The possibility that the direction of the poverty gradient might change over the course of a drug epidemic is discussed.  (+info)

(29/276) An analytic framework fo space-time aberrancy detection in public health surveillance data.

Public health surveillance is changing in response to concerns about bioterrorism, which have increased the pressure for early detection of epidemics. Rapid detection necessitates following multiple non-specific indicators and accounting for spatial structure. No single analytic method can meet all of these requirements for all data sources and all surveillance goals. Analytic methods must be selected and configured to meet a surveillance goal, but there are no uniform criteria to guide the selection and configuration process. In this paper, we describe work towards the development of an analytic framework for space-time aberrancy detection in public health surveillance data. The framework decomposes surveillance analysis into sub-tasks and identifies knowledge that can facilitate selection of methods to accomplish sub-tasks.  (+info)

(30/276) Leukaemia clusters in Great Britain. 1. Space-time interactions.

STUDY OBJECTIVE: The aim was to test a large set of childhood leukaemia and lymphoma registrations for the presence of clusters in space and in time. DESIGN: The study was a space-time cluster analysis. SETTING: England, Wales and Scotland. PATIENTS: All registrations for leukaemia and lymphoma between 1966 and 1983 in children aged 0 to 14 years were examined. The records included date and age of registration, sex, diagnosis, and the map reference of the postcode of residence. Of the 9411 registrations, 8888 were suitable for inclusion. MAIN RESULTS: There was a statistically significant excess of case pairs occurring jointly within 0.5 km and 60 d of each other: 68 pairs compared with 50.0 expected. The excess was detectable in central England, in the north of England and Scotland, but not in the south west of England. It was concentrated within the age band 4 to 7 years and among the lymphatic leukaemias. Several potential artefacts were considered and excluded, but the possibility remained that clustered detections might be triggered by haematological examinations undertaken for some communicable disease. CONCLUSIONS: There was strong evidence of joint spatial-temporal clustering, with an excess of pairs separated by very short time and distance intervals. The causes are probably biological rather than artefactual, but further work will be necessary in order to exclude the latter.  (+info)

(31/276) Leukaemia clusters in Great Britain. 2. Geographical concentrations.

STUDY OBJECTIVE: The aim was to test a large set of childhood leukaemia and lymphoma registrations for the presence of short radius spacial clusters. DESIGN: The study was a geographical cluster analysis. SETTING: England, Wales and Scotland. PATIENTS: All registrations for leukaemia and lymphoma between 1966 and 1983 in children aged 0 to 14 years were examined. The records included date and age of registration, sex, diagnosis, and the map reference of the postcode of residence. Of the 9411 registrations, 8888 were suitable for inclusion. MAIN RESULTS: There was a significant excess of case pair addresses separated by < 0.5 km. There was also a significant excess of pairs sharing the same postcode. Both findings were based upon comparison with random pairs of postcodes drawn from the Central Postcode Directory. Examination for clustering at this very short range was based upon a clear prior hypothesis derived from the results of a study of space-time interaction, reported in a companion paper. CONCLUSIONS: It is postulated that the space-time interaction and the geographical concentrations shown here result from a common epidemic process. The epidemiology of this disease is characterised by short range geographical concentrations, with temporal non-homogeneity superimposed. The findings exclude certain artefacts which remained unresolved in the space-time interaction study. The distributions almost certainly reflect biological processes, and the most probable explanation is in terms of an infective process.  (+info)

(32/276) Statistical inference and model selection for the 1861 Hagelloch measles epidemic.

A stochastic epidemic model is proposed which incorporates heterogeneity in the spread of a disease through a population. In particular, three factors are considered: the spatial location of an individual's home and the household and school class to which the individual belongs. The model is applied to an extremely informative measles data set and the model is compared with nested models, which incorporate some, but not all, of the aforementioned factors. A reversible jump Markov chain Monte Carlo algorithm is then introduced which assists in selecting the most appropriate model to fit the data.  (+info)