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Work Package 2 – Epidemiology

Work Package-leader: Inger Marie Bernhoft, Danmarks Tekniske Universitet, Denmark

The objectives of this work package is to assess the situation in Europe regarding the prevalence of alcohol and other psychoactive substances in drivers in the general traffic and drivers involved in injury accidents, to calculate the accident risk for drug impaired drivers and to identify characteristics of drug impaired drivers.

Several methodological approaches are used both for estimating the prevalence of drug driving and the accident risk for drug impaired drivers, each with different sensitivity and specificity. The prevalence of drug driving is estimated by means of road side surveys and a travel survey and the prevalence of drugs in injury accidents is estimated by means of hospital surveys of seriously injured and killed drivers. Accident risk estimates for drug impaired drivers are based on linkage of results on drugs in drivers in traffic to drugs in injured drivers, on linkage of medication records to accident data and linkage of analyses of accidents with drug impaired drivers to accidents without. Furthermore, characteristics of drivers who have been involved in accidents while drug impaired or convicted for drug driving will be investigated by means of interviews.

The results from various European countries (for example Northern, Western, Southern and Eastern Europe) will be compared in order to reveal any differences regarding use of psychoactive substances.

All studies that require approval from medical ethics committees will be conducted according to the code of ethics on human experimentation established by the declaration of Helsinki (1964) and amended in Edinburgh (2000). Approval for each of the studies will be obtained from the local, independent medical ethics committee by each of the partners. As a consequence of obtaining information on personal data, like National Insurance number, name, address and phone number, the studies that contain such information will also be announced to the national data protection agencies for information or approval, depending on national rules. All persons working in the project are bound to observe professional secrecy. This applies both to researchers, hospital staff and toxicologists. All information are collected and kept strictly confidential so there will be no relation to any individual person. After termination of the project, all data will be destroyed.

Research studies in work package 2 cover prevalence studies and relative risk estimation studies.

1. Prevalence studies

Drugs in the general population: Data about drug consumption in the general population will give information about the size of the problem and about the distribution of specific psychoactive substances in the different European countries. These data will also contribute to the decision regarding which substances should be analysed for in the prevalence studies. An overview of epidemiological research that has proved to give important information will also be carried out.

Prevalence of drugs in the general driving population: Information about the prevalence of drugs in drivers is crucial for road safety policies, that means as the basis for recommendations for the implementation of enforcement strategies as well as recommendations for rehabilitation programmes, including information about the variety of psychoactive substances in the different countries. This information will be collected by means of roadside-surveys in 13 European countries where randomly stopped drivers are checked for drug consumption. These countries are Denmark, Belgium, The Netherlands, Sweden, Finland, Italy, Hungary, Lithuania, Poland, Spain, Czech Republic, Norway and Portugal. Although blood analyses give the most significant results, unfortunately, collection of this specimen will generally not be possible. Therefore analyses of saliva will be used, combined with a breath test for alcohol, and combined with a blood test in a subset of the drivers in some of the countries.

Information on the prevalence of drugs will also be collected in Germany by means of self-reported substance use, collected in interviews over the mobile phone. This method is carried out as an alternative to road side testing.

Prevalence of drugs in crash-involved drivers: In order to get information about the role of various drugs in accident involved drivers, data from drivers who have been involved in a traffic accident are necessary. Blood samples from seriously injured drivers in eight countries will be collected and analysed for drugs in a dedicated co-operation with selected hospitals. These countries are Denmark, Belgium, The Netherlands, Sweden, Finland, Italy, Hungary and Lithuania. In most countries, the data collection will demand informed consent from the drivers.

Prevalence of drugs in drivers involved in fatal accidents: Based on urine screening or blood analysis of drugs in 10.000 drivers involved in fatal accidents, the role of drugs in these accidents will be studied. The study will be carried out in France, as a supplement to the data collections in hospitals.

Driver characteristics: Motives leading to drug driving will be studied by means of semi-structured interviews of drivers who have been charged for drink and drug driving. 30 interviews will be carried out in Sweden and 30 interviews in Hungary in order to compare the motives in two countries with different cultures but both with a zero-tolerance law for driving while impaired by illegal drugs.

Accident causation factors will be sought from 100 drug related accidents by means of in-depth interviews of the drivers, passengers other victims etc. regarding the accident occurrence. The study will be carried out in Italy. Both studies will provide useful information regarding effective measures to prevent drug driving, information addressing the implementation of guidelines to every day medical and pharmaceutical practice, for example use of a language which addresses the psycho-social processes, as well as proposals for personal rehabilitation programmes.

2. Relative risk estimations

Accident risk based on case-control studies: The prevalence of drugs in accident involved drivers based on hospital case studies will be compared to the prevalence of drugs in the general driving population based on road side surveys. The result will be a calculation of the relative risk for drug drivers of being seriously injured in an accident. By means of logistic regression the influence of confounding factors (like gender, age, day of the week and time of the day) can be adjusted for. A relative risk exceeding the value 1 means an increased accident risk for drug impaired drivers. The relative risk will be calculated in the eight countries where the prevalence of drugs in crash-involved drivers is studied, that is Denmark, Belgium, The Netherlands, Sweden, Finland, Italy, Hungary and Lithuania.

Accident risk based on pharmacoepidemiology: Relative accident risk will be estimated for different medicines on the base of a comparison of individual medication records with the respective accident data of the same person. One important outcome will be the impact of specific medicinal drug use patterns, such as the differences within the same therapeutic class of drugs (for example differences between short- and long-acting benzodiazepines), furthermore the risk associated with the first weeks or months after the start of medication. The study will be carried out in the Netherlands.

Culpability studies: In this type of study a distinction is made between drivers who are responsible for the accident and those who are not. The former are taken as cases and the latter as controls, for determining the odds ratio for responsibility for traffic accidents under the influence of a certain substance. It is important that the assessment of culpability will be conducted without knowing if the driver was under influence or not. Culpability studies will result in estimates of accident risk for the most frequently used substances. Studies based on fatal accidents will be carried out in France and Finland and a third study will focus on a comparison between Germany, Sweden and Lithuania.

Relative risk estimates will serve as input to various studies in other work packages, for example regarding recommendations for thresholds of drug concentrations in relation to traffic safety, classification of medicines and guidelines to medical and pharmaceutical practice.

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