A modelling approach to support dynamic decision-making in the control of FMD epidemics.

Most studies on control strategies for contagious diseases such as foot-and-mouth disease (FMD) evaluate pre-defined control strategies and imply static decision-making during epidemic control. Such a static approach contradicts the dynamic nature of the decision-making process during epidemic control. This paper presents an integrated epidemic-economic modelling approach to support dynamic decision-making in controlling FMD epidemics. This new modelling approach reflects ongoing uncertainty about epidemic growth during epidemic control and provides information required by a dynamic decision process. As demonstrated for a Dutch FMD-case, the modelling approach outperforms static evaluation of pre-fixed control strategies by: (1) providing guidance to decision-making during the entire control process; and (2) generating more realistic estimation of the costs of overreacting or underreacting in choosing control options.

Effectiveness of simulated interventions in reducing the estimated prevalence of E. coli O157:H7 in lactating cows in dairy herds.

A transmission model developed to investigate the dynamics of Escherichia coli O157:H7 bacteria in a typical Dutch dairy herd was used to assess the effectiveness of vaccination, diet modification, probiotics (colicin) and hygienic measures as to water troughs and bedding, when they are applied single or in combination, in reducing the prevalence of infected animals. The aim was to rank interventions based on their effectiveness in reducing the baseline prevalence of infected animals in the lactating group. The baseline prevalence of the lactating group and the within-herd prevalence were estimated by the model to be 5.02% and 13.96% respectively. The results show that all four interventions, if applied to all four animal groups or only to young stock, are the most effective and will reduce the baseline prevalence by 84% to 99%. In general, combinations of hygiene (applied in all groups) and one other intervention had the highest effectiveness in reducing prevalence in the lactating group. Vaccination and diet modification show a slightly higher effectiveness than colicin and hygiene.

Sensitivity analysis to evaluate the impact of uncertain factors in a scenario tree model for classical swine fever introduction.

Introduction of classical swine fever virus (CSFV) is a continuing threat to the pig production sector in the European Union. A scenario tree model was developed to obtain more insight into the main risk factors determining the probability of CSFV introduction (P(CSFV)). As this model contains many uncertain input parameters, sensitivity analysis was used to indicate which of these parameters influence model results most. Group screening combined with the statistical techniques of design of experiments and meta-modeling was applied to detect the most important uncertain input parameters among a total of 257 parameters. The response variable chosen was the annual P(CSFV) into the Netherlands. Only 128 scenario calculations were needed to specify the final meta-model. A consecutive one-at-a-time sensitivity analysis was performed with the main effects of this meta-model to explore their impact on the ranking of risk factors contributing most to the annual P(CSFV). The results indicated that model outcome is most sensitive to the uncertain input parameters concerning the expected number of classical swine fever epidemics in Germany, Belgium, and the United Kingdom and the probability that CSFV survives in an empty livestock truck traveling over a distance of 0-900 km.

Simulating Escherichia coli O157:H7 transmission to assess effectiveness of interventions in Dutch dairy-beef slaughterhouses.

Beef contamination with Escherichia coli O157:H7 (VTEC) is an important food-safety issue. To investigate the effectiveness of interventions against VTEC in Dutch beef industrial slaughterhouses that slaughter 500 dairy cattle per day, a Monte Carlo simulation model was built. We examined seven carcass-antimicrobial interventions, namely: hot-water wash, lactic-acid rinse, trim, steam-vacuum, steam-pasteurization, hide-wash with ethanol and gamma irradiation, and their combinations. The estimated daily prevalence of contaminated beef-carcass quarters as the output of the model was 9.2%. Contaminated was defined as containing one or more CFU on the surface of a carcass quarter at the end of the quartering stage. Single interventions (except irradiation) could reduce the prevalence to from 6.2% to 1.7%, whereas the combination of interventions could lower it to from 1.2% to 0.1%. The most powerful intervention was irradiation, which could reduce the prevalence to <0.1%. The results of this study indicate that application of single interventions might be useful, although not sufficient. Hence, a combination of interventions along the slaughter process is the more promising approach to reduce the prevalence of contaminated beef quarters.

Risk factors for sick leave due to musculoskeletal disorders among self-employed Dutch farmers: a case-control study.

BACKGROUND: In Dutch agriculture, musculoskeletal disorders are a main cause of sick leave. Among self-employed insured farmers, neck, shoulder, upper extremity, and back disorders accounted for 30% of the claims for sick leave of less than 1 year This case-control study set out to identify and quantify risk factors for sick leave due to musculoskeletal disorders among self-employed Dutch farmers. METHODS: Sick leave, claimed at an insurance company from 1998 to 2001 for back (SL-BP, n = 198) or neck/shoulder/upper extremity trouble (SL-EXT, n = 89) was analyzed; the controls did not file any claim in this period (n = 816). RESULTS: Multivariate analysis showed that risk factors for SL-BP were increased age (OR = 1.06 per year, CI = 1.04-1.09), body mass index (BMI) >27 (OR = 1.93, CI = 1.2-3.2), smoking (OR = 1.90, CI = 1.2-2.9), former pain (OR = 3.28, CI = 2.1-5.1), tractor driving >1,000 hr/year (OR = 2.44, CI = 1.0-6.4), and "high work pace and workload" (OR = 1.59, CI = 1.0-2.4). SL-EXT was associated with pig (OR = 3.63, CI = 1.4-9.7), mushroom (OR = 6.14, CI = 1.4-27.2), or dairy/pig farming (OR = 4.56, 1.1-19.5), while age (OR = 1.10, CI = 1.06-1.14), smoking (OR = 1.79, CI = 1.0-3.2), and former pain (OR = 3.37, CI = 1.9-6.1) were also contributing. CONCLUSIONS: Prevention of sick leave of self-employed farmers should focus on life style (obesity, smoking), reducing older farmers' exposure to physical load, exposure to long-term tractor driving. Specific attention should be paid to animal and mushroom farmers.

Scenario tree modeling to analyze the probability of classical swine fever virus introduction into member states of the European Union.

The introduction of classical swine fever virus (CSFV) into a country free of disease without vaccination may have huge consequences in terms of both disease spread and economic losses. More quantitative insight into the main factors determining the probability of CSFV introduction (PCSFV) is needed to optimally use resources for the prevention of CSFV introduction. For this purpose a spreadsheet model was constructed that calculates the annual PCSFV into member states of the European Union (EU). The scenario pathway approach was used as most probabilities in the model are very small. Probability distributions were used to take into account inherent variability of input parameters. The model contained pathways of CSFV introduction including the import of pigs and pork products, returning livestock trucks, and contacts with wild boar. All EU member states were included as possible sources of CSFV. Default results for the Netherlands showed a mean overall annual PCSFV of approximately 0.06, indicating that the Netherlands can expect CSFV introduction on average once every 18 years from the pathways and countries included in the model. Almost 65% of this probability could be attributed to the pathway of returning livestock trucks. The most likely sources of CSFV introduction were Germany, Belgium, and the United Kingdom. Although the calculated probabilities were rather low when compared with expert estimates and recent history, the most likely causes of CSFV introduction indicated by the model were considered to be realistic. It was therefore concluded that the model is a useful tool to structure and analyze information for decision making concerning the prevention of CSFV introduction.