[Show abstract][Hide abstract] ABSTRACT: A Bayesian latent class model was used to estimate the sensitivity and specificity of an immunoglobulin G1 serum enzyme-linked immunosorbent assay (Paralisa) and individual fecal culture to detect young deer infected with Mycobacterium avium subsp. paratuberculosis. Paired fecal and serum samples were collected, between July 2009 and April 2010, from 20 individual yearling (12-24-month-old) deer in each of 20 South Island and 18 North Island herds in New Zealand and subjected to culture and Paralisa, respectively. Two fecal samples and 16 serum samples from 356 North Island deer, and 55 fecal and 37 serum samples from 401 South Island deer, were positive. The estimate of individual fecal culture sensitivity was 77% (95% credible interval [CI] = 61-92%) with specificity of 99% (95% CI = 98-99.7%). The Paralisa sensitivity estimate was 19% (95% CI = 10-30%), with specificity of 94% (95% CI = 93-96%). All estimates were robust to variation of priors and assumptions tested in a sensitivity analysis. The data informs the use of the tests in determining infection status at the individual and herd level.
Preview · Article · Oct 2013 · Journal of veterinary diagnostic investigation: official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc
[Show abstract][Hide abstract] ABSTRACT: Until recently New Zealand had one of the highest rates of human campylobacteriosis reported by industrialized countries. Since the introduction of a range of control measures in the poultry production chain a reduction in human cases of around 50% has been observed nationwide. To inform risk managers a combination of spatial, temporal and molecular tools - including minimum spanning trees, risk surfaces, rarefaction analysis and dynamic source attribution modelling - was used in this study to formally evaluate the reduction in disease risk that occurred after the implementation of control measures in the poultry industry. Utilizing data from a sentinel surveillance site in the Manawatu region of New Zealand, our analyses demonstrated a reduction in disease risk attributable to a reduction in the number of poultry-associated campylobacteriosis cases. Before the implementation of interventions poultry-associated cases were more prevalent in urban than rural areas, whereas for ruminant-associated cases the reverse was evident. In addition to the overall reduction in prevalence, this study also showed a stronger intervention effect in urban areas where poultry sources were more dominant. Overall a combination of molecular and spatial tools has provided evidence that the interventions aimed at reducing Campylobacter contamination of poultry were successful in reducing poultry-associated disease and this will inform the development of future control strategies.
No preview · Article · Aug 2011 · Preventive Veterinary Medicine
[Show abstract][Hide abstract] ABSTRACT: Combining data sources is often seen as a panacea, having the potential to produce more to produce cost-effective, accurate, fine-level statistics for a lower cost. This paper clarifies conditions under which Official Statistics data sources, particularly surveys and censuses or surveys and administrative sources, should and should not be combined using statistical models based on mass imputation, spatial microsimulation, and small area and domain estimation. The theoretical links between these three techniques are explored. The wider research from which this paper is a report considers the relevant literature in depth, further develops existing statistical methods, considers their application in principle to set of case studies in sociology, economics, and business, and provides guidelines for use of the three techniques based on this research.
[Show abstract][Hide abstract] ABSTRACT: Integrated surveillance of infectious multi-source diseases using a combination of epidemiology, ecology, genetics and evolution can provide a valuable risk-based approach for the control of important human pathogens. This includes a better understanding of transmission routes and the impact of human activities on the emergence of zoonoses. Until recently New Zealand had extraordinarily high and increasing rates of notified human campylobacteriosis, and our limited understanding of the source of these infections was hindering efforts to control this disease. Genetic and epidemiological modeling of a 3-year dataset comprising multilocus sequence typed isolates from human clinical cases, coupled with concurrent data on food and environmental sources, enabled us to estimate the relative importance of different sources of human disease. Our studies provided evidence that poultry was the leading cause of human campylobacteriosis in New Zealand, causing an estimated 58-76% of cases with widely varying contributions by individual poultry suppliers. These findings influenced national policy and, after the implementation of poultry industry-specific interventions, a dramatic decline in human notified cases was observed in 2008. The comparative-modeling and molecular sentinel surveillance approach proposed in this study provides new opportunities for the management of zoonotic diseases.
No preview · Article · Sep 2009 · Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases
[Show abstract][Hide abstract] ABSTRACT: A Bayesian approach was developed by Hald et al.((1)) to estimate the contribution of different food sources to the burden of human salmonellosis in Denmark. This article describes the development of several modifications that can be used to adapt the model to different countries and pathogens. Our modified Hald model has several advantages over the original approach, which include the introduction of uncertainty in the estimates of source prevalence and an improved strategy for identifiability. We have applied our modified model to the two major food-borne zoonoses in New Zealand, namely, campylobacteriosis and salmonellosis. Major challenges were the data quality for salmonellosis and the inclusion of environmental sources of campylobacteriosis. We conclude that by modifying the Hald model we have improved its identifiability, made it more applicable to countries with less intensive surveillance, and feasible for other pathogens, in particular with respect to the inclusion of nonfood sources. The wider application and better understanding of this approach is of particular importance due to the value of the model for decision making and risk management.
[Show abstract][Hide abstract] ABSTRACT: This study quantifies the spatio-temporal association between outbreaks of highly pathogenic avian influenza H5N1 in domestic poultry (n = 3050) and human cases (n = 99) in Vietnam during 2003-2007, using rare events logistic regression. After adjusting for the effect of known confounders, the odds of a human case being reported to authorities increased by a factor of 6.17 [95% confidence interval (CI) 3.33-11.38] and 2.48 (95% CI 1.20 - 5.13) if poultry outbreaks were reported in the same district 1 week and 4 weeks later respectively. When jointly considering poultry outbreaks in the same and neighbouring districts, occurrence of poultry outbreaks in the same week, 1-week later, and 4 weeks later increased the odds of a human case by a factor of 2.75 (95% CI 1.43-5.30), 2.56 (95% CI 1.31-5.00) and 2.70 (95% CI 1.56-4.66) respectively. Our study found evidence of different levels of association between human cases and poultry outbreaks in the North and the South of the country. When considering the 9-week interval extending from 4 weeks before to 4 weeks after the week of reporting a human case, in the South poultry outbreaks were recorded in 58% of cases in the same district and 83% of cases in either the same or neighbouring districts, whereas in the North the equivalent results were only 23% and 42%. The strength of the association between human and poultry cases declined over the study period. We conclude that owner reporting of clinical disease in poultry needs to be enhanced by targeted agent-specific surveillance integrated with preventive and other measures, if human exposure is to be minimized.
No preview · Article · Jul 2009 · Transboundary and Emerging Diseases
[Show abstract][Hide abstract] ABSTRACT: The motivation for this work was to investigate the possibility of accurately determining the age of a tern chick using easily
obtained body measurements. We describe the construction of a nonlinear multivariate hierarchical model for chick growth and
show how it can be estimated using Markov chain Monte Carlo techniques. A simple extension of the analysis allows for estimation
of the ages of unknown chicks. Posterior distributions of the unknown ages are derived, so that the accuracy of age determination
can be examined. We further extend our model and analysis to include the possibility that chicks fall into distinct groups
with different growth characteristics. The technique is illustrated using data on the weight and wing length of black-fronted
terns from the Ohau River, New Zealand. It is found that dating to within one day is possible, but only in some areas of the
data space. The concept of “braiding” of multivariate growth curves is introduced to explain the varying accuracy of age determination.
No preview · Article · Sep 2005 · Journal of Agricultural Biological and Environmental Statistics