Quantitative Assessment of High School Students' Poly-drug Use: Related Social Aspects and School Dropout.

INTRODUCTION: Poly-drug use has increased in recent decades, especially in young drugusing groups. Classic epidemiological indicators of drug use, such as prevalence and incidence of users of specific substances, are not adequate as measures of the possible harms of poly-drug use. We applied poly-drug use indicators, based on substance-specific harm scores reported by van Amsterdam and Nutt in 2015, to data from high school student surveys, showing their usefulness in identifying high-risk drug consumption. Analysing the 'correlation' between high-risk drug use of high school students and school dropout allows the evaluation of adopted prevention policies and may suggest more suitable approaches. METHODS: Each drug user is characterized by two specific scores: overall frequency of use of substances during the period of interest (FUS) and poly-drug use score (PDS). The poly-drug use score is a weighted average of the harm scores of the individual substances used multiplied by their respective frequencies of use. The PDS increases with the frequency of use, with the number of substances used, and with the specific harm scores of each substance. This indicator consists of two components, one representing the health harm score toward self and the other the social harm score toward others. RESULTS: The indicators have been applied to sample data involving youth population, specifically the ESPAD®Italia survey data on high school students conducted annually in Italy. The trends of poly-drug use at different ages of students, 15-19 years, over time, and gender have been studied. The results have been linked to educational outcomes, early school leaving and social aspects, making it possible to assess present prevention interventions and suggest appropriate planning of future prevention interventions. CONCLUSION: Poly-drug use indicators allow a comprehensive quantitative evaluation of the risks of drug use. The analysis of the links between heavy use of drugs, school performance and dropout, and the social variables that influence them, shown in this work, suggests how best to plan secondary or indicated prevention interventions at school. The problem of including "new" NPS in analyses is also briefly discussed.

Cost-effectiveness of varicella and herpes zoster vaccination in Sweden: An economic evaluation using a dynamic transmission model.

OBJECTIVES: Comprehensive cost-effectiveness analyses of introducing varicella and/or herpes zoster vaccination in the Swedish national vaccination programme. DESIGN: Cost-effectiveness analyses based on epidemiological results from a specifically developed transmission model. SETTING: National vaccination programme in Sweden, over an 85- or 20-year time horizon depending on the vaccination strategy. PARTICIPANTS: Hypothetical cohorts of people aged 12 months and 65-years at baseline. INTERVENTIONS: Four alternative vaccination strategies; 1, not to vaccinate; 2, varicella vaccination with one dose of the live attenuated vaccine at age 12 months and a second dose at age 18 months; 3, herpes zoster vaccination with one dose of the live attenuated vaccine at 65 years of age; and 4, both vaccine against varicella and herpes zoster with the before-mentioned strategies. MAIN OUTCOME MEASURES: Accumulated cost and quality-adjusted life years (QALY) for each strategy, and incremental cost-effectiveness ratios (ICER). RESULTS: It would be cost-effective to vaccinate against varicella (dominant), but not to vaccinate against herpes zoster (ICER of EUR 200,000), assuming a cost-effectiveness threshold of EUR 50,000 per QALY. The incremental analysis between varicella vaccination only and the combined programme results in a cost per gained QALY of almost EUR 1.6 million. CONCLUSIONS: The results from this study are central components for policy-relevant decision-making, and suggest that it was cost-effective to introduce varicella vaccination in Sweden, whereas herpes zoster vaccination with the live attenuated vaccine for the elderly was not cost-effective-the health effects of the latter vaccination cannot be considered reasonable in relation to its costs. Future observational and surveillance studies are needed to make reasonable predictions on how boosting affects the herpes zoster incidence in the population, and thus the cost-effectiveness of a vaccination programme against varicella. Also, the link between herpes zoster and sequelae need to be studied in more detail to include it suitably in health economic evaluations.

Some model based considerations on observing generation times for communicable diseases.

The generation time of an infectious disease is usually defined as the time from the moment one person becomes infected until that person infects another person. The concept is similar to "generation gap" in demography, with new infections replacing births in a population. Originally applied to diseases such as measles where at least the first generations are clearly discernible, the concept has recently been extended to other diseases, such as influenza, where time order of infections is usually much less apparent. By formulating the relevant statistical questions within a simple yet basic mathematical model for infection spread, it is possible to derive theoretical properties of observations in various situations e.g. in "isolation", in households, or during large outbreaks. In each case, it is shown that the sampling distribution of observations depends on a number of factors, usually not considered in the literature and that must be taken into account in order to achieve unbiased inference about the generation time distribution. Some implications of these findings for statistical inference methods in epidemic spread models are discussed.

Estimating the incidence, prevalence and clinical burden of hepatitis C over time in Italy.

Our objective was to estimate HCV clinical burden over time in Italy. A national age-specific HCV prevalence in 1995 was obtained from studies conducted in general population samples and intravenous drug users. Age profile of new HCV infections and trend of incidence since 1985 were derived from a database of reported acute HCV infections. These incidence and prevalence data were used to estimate HCV burden from 1950 to 2030 by mathematical modelling. Different rates of HCV related liver disease progression were tested to assess the robustness of estimates. It is estimated that HCV had a major spread in Italy in 1945-1969. HCV RNA-positive subjects peaked around 1970; their prevalence in 2005 was 3.2%, 58% of them being >65 y of age. The number of individuals with HCV related cirrhosis and that of HCV liver related deaths peaked in 1980-1985. In 2005, they were approximately 230,000 (range 150,000-240,000, according to lower or higher disease progression rates) and approximately 7,000 (range 2200-12,300), respectively: both will be halved by 2025. In conclusion, unlike other industrialized countries, the burden of clinically relevant HCV-positive cases in Italy is already on the decline and will further reduce in the future. This is due to differences in the age-specific prevalence, most of HCV-positive Italians currently being >65 y of age.