Terminology and data
The prevalence of a disease measures the number of cases of existing disease in the population at a given time, or over a period such as the past 12 months. It is calculated as the number of people with the disease divided by the total population, and is usually expressed as a percentage. Age- and sex- specific prevalences can also be calculated. The prevalence of a disease can be difficult to measure directly as these data are usually not collected routinely. In this book, we present information for a number of countries on the prevalence of asthma and COPD derived through multi-centre cross-sectional surveys which have used the same methodology. Data on some other conditions, such as cystic fibrosis and occupational lung diseases, are available through local or national registries.
The incidence of a disease measures the number or rate of new cases of disease occurring in the population, over a specified period such as 12 months. Annual incidence is calculated as the number of new cases of a disease occurring in 12 months divided by the population who were disease-free at the beginning of the period. Incidence can be hard to measure, as it involves knowing who was disease-free at the beginning of the period. Incidence data for lung cancer, tuberculosis and certain occupational diseases are available through routine data collection sources and are usually related to an estimate of the mid-year population. Incidence data for other diseases and conditions are sparse.
Deaths are coded to an underlying cause using conventions established by the WHO’s International Classification of Diseases (ICD). Mortality data are available for European countries coded under the ICD-10, ICD-9 and ICD-8 revisions. In the data presented here, most countries used ICD-10 coding, usually individual ICD-10 codes, although a few used one of two ICD-10 condensed lists or an ICD-9 condensed list and Turkey used an ICD-8 condensed list. A list of the required respiratory conditions with ICD-10 codes was drawn up and a mapping exercise carried out to ascertain the equivalent ICD-9 and ICD-8 codes. The World Detailed Mortality Database (World DMDB, November 2011 update) was used as the primary source and numbers of deaths and corresponding populations by year, sex and 5-year age-group for 50 European countries were extracted. For each country, the latest available year of data was used (2005–2010). No data were available for Bosnia & Herzegovina, and no recent data were available for Turkmenistan (latest available 1998). For countries not reporting by individual ICD-10 codes, data for some conditions, such as asthma and COPD, were not available. To increase coverage, the WHO Europe Detailed Mortality Database was also downloaded (Europe DMDB, last accessed February 2012) as this database contains deaths coded by individual ICD-9 codes.
Admissions are episodes of hospital in-patient care, classified by ICD coding on discharge. They are a measure of health service utilisation and reflect local medical care practices, data coding and recording patterns as well as the epidemiology of the conditions described. Since admissions are a complex outcome (measuring episodes or patients, including or excluding transfers and emergency admissions and sometimes covering multiple comorbidities), in this book we present admissions data from two large international databases – the WHO Europe Hospital Morbidity Database (HMDB) and data from the European Commission statistics agency, Eurostat – for greater comparability. This publication uses information from HMDB where available, supplemented with Eurostat data. Data are available from the WHO database on hospital admissions (discharges and deaths), day-cases, and bed-days for 27 European countries. Eurostat supplies discharge data for 30 countries of which nine supplement the HMDB data. These are available for a limited set of conditions on the International Short Hospital Morbidity Tabulation (HMT). For some countries in the Eurostat database (Bulgaria, Estonia, Romania, Sweden), data are only available for all ages combined so for these countries, admission rates for age-specific conditions (childhood and adult asthma, paediatric respiratory disease and acute lower respiratory infections in adults) are not available.
In this book, most of the country-specific hospital admission and mortality rates presented are age-standardised to the European Standard Population. The age-standardised rate for a particular disease or condition is calculated by applying the country’s age-specific rates to the standard population. This enables comparisons to be made between countries with different age-structures and time-periods. As some conditions vary with age, countries with a relatively high proportion of elderly people might have proportionately more cases. The European Standard Population is the same for males and females.