Version 10 of the QRESEARCH database was used for this analysis. This database contains representative anonymised aggregated health data derived from 422 general practices throughout England. Although these practices are self-selected, they are broadly representative of primary care practices in the UK.8
Data for this analysis were available for the period 1 January 2001 to 31 December 2005. Data were extracted for the period 1 January 2001 (2 885 724 patients) to 31 December 2005 (2 968 495 patients). The same practices were used throughout the study period. The methods used to collect primary care data for the QRESEARCH database have been previously described.9–12
In the UK, the majority of individuals resident (including children) are registered with primary care, which is free at the point of contact. Patients were included if they were registered on the first day of each year (for example, 1 January 2001) and were registered for the preceding 12 months. Those with incomplete data, that is, temporary residents, newly registered patients, and those who joined, left, or died during each study year were excluded. Patients were considered to have physician-diagnosed COPD if they had a relevant computer-recorded diagnostic Read Code (Box 1
) in their electronic health record during the time period of interest.
Box 1. Chronic obstructive pulmonary disease Read Codes used in these analyses.
|Read Code||Read term|
|H3…||Chronic obstructive pulmonary disease|
|H310||Simple chronic bronchitis|
|H3100||Chronic catarrhal bronchitis|
|H310z||Simple chronic bronchitis NOS|
|H311.||Mucopurulent chronic bronchitis|
|H3110||Purulent chronic bronchitis|
|H3111||Fetid chronic bronchitis|
|H311z||Mucopurulent chronic bronchitis NOS|
|H312.||Obstructive chronic bronchitis|
|H3120||Chronic asthmatic bronchitis|
|H3210-1||Chronic wheezy bronchitis|
|H3122||Acute exacerbation of chronic obstructive airways disease|
|H312z||Obstructive chronic bronchitis NOS|
|H313.||Mixed simple and mucopurulent chronic bronchitis|
|H31y.||Other chronic bronchitis|
|H31yz||Other chronic bronchitis NOS|
|H31z.||Chronic bronchitis NOS|
|H320.||Chronic bullous emphysema|
|H3200||Segmental bullous emphysema|
|H3201||Zonal bullous emphysema|
|H3202||Giant bullous emphysema|
|H3203||Bullous emphysema with collapse|
|H320z.||Chronic bullous emphysema NOS|
|H32y0||Acute vesicular emphysema|
|H32y1||Atrophic (senile) emphysema|
|H32y2||Acute interstitial emphysema|
|H32yz||MacLeod’s unilateral emphysema|
|H32yz-1||Other emphysema NOS|
|H37..||Mild chronic obstructive pulmonary disease|
|H38..||Moderate chronic obstructive pulmonary disease|
|H3y..||Severe chronic obstructive pulmonary disease|
|H3y-1||Other specified chronic obstructive airways disease|
|H3y0||Chronic obstructive pulmonary disease with acute lower respiratory infection|
|H3y1||Chronic obstructive pulmonary disease with acute exacerbation, unspecified|
|H3z..||Chronic obstructive airways disease NOS|
Incidence rate was defined as the number of patients with a new case of physician-diagnosed COPD in a specific year, with the denominator being the number of patient-years of observation (calculated from the number of patients who were registered with practices for the entire year). Lifetime prevalence was defined as the proportion of people with COPD ever diagnosed by a physician, recorded (that is, on at least one occasion) in the GP records prior to the end of each study year (for example, before 31 December 2001); the denominator used to calculate the lifetime prevalence was the number of patients registered with the study practices at the end of each study year (for example, 31 December 2001). Smokers were defined as the proportion of patients with physician-diagnosed COPD and a smoking status code (Read Code: 137 and below) in the last 5 years recorded as a current smoker (in the year of study). Consultation rates (for any reason) per person per year were calculated. These included consultation with a GP or nurse in the home, at the surgery, and/or on the telephone.
How this fits in
In England, there is growing concern that the disease burden and healthcare costs associated with chronic obstructive disease (COPD) will continue to rise. This study found a large rise in the lifetime prevalence of physician-diagnosed COPD between 2001 and 2005, but a peak in the incidence rate. Although we may be approaching the peak of the COPD incidence and prevalence in England, the number of people affected remains high and poses a major challenge for health services, particularly those in the north east of the country and in the most deprived communities in England where high rates of COPD exist. The very limited decrease in smoking rates among the more deprived groups of patients with COPD is also a cause for concern.
Socioeconomic deprivation was defined on the basis of the Townsend score associated with the output area of the patient’s postcode. The Townsend score is a composite score based on unemployment, overcrowding, lack of car, and non-owner occupancy. Higher scores indicate greater levels of socioeconomic deprivation. The cut-offs for the quintiles are based on the national distribution of Townsend scores derived from the 2001 Census.
Because of known age and sex variations, rates of disease were standardised by sex and 5-year age bands. The mid-year population estimates for England in each year of study were used as the reference population and to estimate the actual number of people with COPD in England.13
test was used to compare categorical variables in different groups of patients. The Mantel-Haenszel χ2
test was used to investigate trends over time, this analysis was undertaken using EpiInfo2000 (World Health Organization, Geneva, Switzerland). Where appropriate, 95% confidence intervals (CIs) are reported.