JRSM >
Volume 101, Number 9 >
Pp. 466-472
1 Ayr Hospital
2 Community Health Sciences, University of Nottingham
3 University of Manchester
4 Division of Community Health Sciences: GP Section, University of Edinburgh 20 West Richmond Street, Edinburgh EH8 9DX, UK
Correspondence to: Aziz Sheikh aziz.sheikh{at}ed.ac.uk
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Design Analysis of primary healthcare datasets.
Setting The UK prevalence of allergic rhinitis has increased very significantly over recent decades. Analysis of primary healthcare datasets offers the possibility to advance understanding about the changing epidemiology and management of allergic rhinitis. QRESEARCH is one of the world's largest national aggregated health databases containing the records of over nine million patients. We extracted data on all patients with a recorded diagnosis of allergic rhinitis and calculated annual age–sex standardized incidence and lifetime period prevalence rates for each year from 2001–2005. We also analysed prescribing trends for antihistamines and drugs used in nasal allergy in those with a recorded diagnosis of allergic rhinitis.
Main outcome measures Age-sex standardized incidence, lifetime prevalence rates and prescribing trends for symptom relief medication for allergic rhinitis in England.
Results The age-sex standardized incidence of allergic rhinitis was 5.57 per 1000 person-years in 2001 and increased by 33.0% to 7.41 per 1000 person-years in 2005 (P<0.001). Lifetime age-sex standardized prevalence of a recorded diagnosis of allergic rhinitis increased by 43.2% from 46.35 per 1000 in 2001 to 66.37 per 1000 in 2005 (P<0.001). Over this period a 41.7% overall increase in prescriptions for antihistamines and drugs used in nasal allergy was observed (antihistamines 45.5%, drugs used in nasal allergies 35.5%).
Conclusions Recorded incidence and lifetime prevalence of allergic rhinitis have increased substantially in recent years. A similar increase in prescriptions for antihistamines and drugs used in nasal allergy in patients with allergic rhinitis is also observed.
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The International Study of Asthma and Allergies in Childhood (ISAAC) epidemiological research programme recently published data of their 2002–2003 Phase Three study;2 this survey compared data from the baseline Phase One study (completed a mean of seven years after Phase One).4 Both phases of this international cross-sectional survey enquired about symptoms indicative of allergic rhinitis over a 12-month period in school-aged children. Results showed that in the UK, the 12-month period prevalence of self-reported symptoms of allergic rhinitis was 15.3% in 13–14 year-olds, a fall of 3.6% from Phase One. In 6–7 year-olds, the 2002–2003 12-month prevalence of self reported symptoms was 10.1%, an increase of 0.3% from Phase One.
In adults, data from the Health Survey for England (HSE) found that the 12-month period prevalence of symptoms was 15% in 2001, this being unchanged from the 1996 figures.3 Results from the European Community Respiratory Health Survey (ECRHS) conducted in 1994 showed that for four British towns and cities, the self-reported prevalence of ever having a diagnosis of hayfever or nasal allergy ranged from 23.6–29.2%.5
Whilst the above data provide useful information on variations in lifetime/period prevalence of self-reported symptoms of allergic rhinitis over time, particularly in children and adolescents, relatively little reliable national data describes clinician diagnosis of allergic rhinitis and changes in the epidemiology for the whole adult population over time. Exploitation of large national healthcare datasets, with their key strengths of large numbers and representative data, offers an important opportunity to develop insights into the epidemiology of allergic rhinitis and associated prescribing.6
Studying primary care databases provides a window onto overall national trends, something that is not possible with large scale surveys such as ISAAC (which has studied only children) and ECRHS (which looks only at adults).7 Building on our previous work,1,3,8 we sought to describe recent trends in recorded primary care diagnosis of allergic rhinitis and prescribing for allergic rhinitis in England.
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Patients were included in the analysis year if they were registered for the entire analysis year in question. Patients who might have incomplete data (i.e. temporary residents, newly registered patients and those who joined, left or died during the year) were not eligible for inclusion. Data for a total of 2,958,366 patients was analysed.
We considered patients to have allergic rhinitis if they had a computer-recorded diagnostic Read code for allergic rhinitis in their electronic health record for the relevant time period. Details regarding the Read codes used are available from the corresponding author.
Incidence was defined as the number of new cases of disease diagnosed and recorded in a specific year, with the denominator of number of patient years of observation (this being calculated as a product of the number of patients registered with practices and their length of registration) being used to calculate incidence rates. Lifetime prevalence was defined as the numbers of people with a diagnosis of allergic rhinitis recorded in the GP records on at least one occasion at any point in their lives; the denominator used to calculate the lifetime prevalence rate was the number of patients registered with the study practices.
For the general population we have determined the consultation rates per person per year with a GP and with a nurse. This includes consultations in the home, at the surgery and on the telephone. We have also determined the consultation rate per person per year for patients with each specific disease regardless of the reason for those consultations. Note that the requirements for patients to be registered for the whole of the analysis year lead to slight under-estimates of consultation rates in the very young and the very elderly populations.10
Because of the known age and sex variations, we standardized rates by sex and five-year age bands using the estimated mid-year population estimates for England in each year as our reference population. These results were then scaled up to estimate the actual numbers of people with allergic rhinitis in England. In order to better estimate the actual numbers of people affected by allergic rhinitis, we calculated 95% confidence intervals around these estimates of lifetime prevalence and absolute numbers of people affected in 2005.11
In order to describe trends in prescribing of antihistamines and nasal preparations of anti-allergic medication, for each of the five years we extracted linked prescribing data in those with a recorded diagnosis of allergic rhinitis and estimated numbers of prescriptions prescribed for both antihistamines and other more specific drugs used for the treatment of nasal allergy listed in chapter 12.2.1 of the British National Formulary (topical nasal corticosteroids, topical nasal antihistamines and topical nasal cromoglicate). Not all patients issued prescriptions in general practice actually present them to pharmacies for dispensing; estimates based on issued prescriptions may therefore be different from Prescribing Analysis and Cost (PACT) data.
We used the Chi Square Mantel-Haenszel test for trend using Epi Info software to test for trends over time.12
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Considering findings in relation to the published literature
Table 5 summarizes previous published epidemiological data for allergic rhinitis. Data from our work show that lifetime clinician-recorded prevalence peaks in the teenage years, and these results are in keeping with data from latest ISAAC study data.2 However, one major difference is the change in prevalence of allergic rhinitis in teenagers between these two studies. Whilst ISAAC Phase Three shows a small fall in period prevalence from Phase One for self-reported symptoms of allergic rhinitis, our data show an increase in lifetime prevalence for a recorded diagnosis of allergic rhinitis. This discordance may reflect improved diagnosis and recording. The female preponderance for prevalence and increased consultation rates for females after the teenage years has also been identified in recent UK data describing presentation of allergic rhinitis in primary care .13
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Main strengths and limitations of this work
The main strengths of this study include our interrogation of an extremely large nationally represen tative dataset, the fact that all contributing practices used the same computing systems for electronically recording clinical data and the approach used to ensure that all contributing practices were accustomed to electronically recording routine data. The study design means that it was not subject to selection bias due to non-responders or recall bias. Another strength of this study is the use of clinician recording of a diagnosis of allergic rhinitis, as opposed to self-reporting of symptoms from previous studies.2,4,5 Although figures for self-reporting of symptoms may correlate to actual prevalence, the role of a clinician assessing a patient minimizes inappropriate diagnosis.
There are a number of limitations that need to be considered when using databases of routinely collected data and these all potentially apply to this work. Most importantly, we were dependant on physician-recorded diagnosis of allergic rhinitis and there may have been improvements in recording of allergic rhinitis over this time period. The relatively short time window over which trends were studied is another limitation, but this does also have the advantage of confining analysis to a period during which there were no changes in disease definition or classification. Data regarding childhood prevalence may be underestimated, as clinician recording of diagnosis will be dependent on parents bringing their children for consultation. This is a recognized problem when using routine general practice data for research, and has been highlighted by previous research using general practice data.15
Conclusions and implications for future research
This large national study reveals that the recorded incidence and lifetime prevalence of allergic rhinitis has increased in England during the first half of this decade, which may reflect a genuine increase in the incidence of allergic rhinitis. Given the findings from a large recent UK case control study that allergic rhinitis in adolescents is associated with underperformance in summer school examinations,16 a key important unanswered question concerns the quality of care and symptom control of these patients.17 The House of Lords Allergy Inquiry, published in 2007, has identified several issues highlighted by our work and other previous research that require further attention.18 These include: maintaining clinical surveillance systems to monitor allergic disease; calling for further research into the ways in which the indoor environment influences allergy development; reviewing how children with allergic rhinitis are supported throughout the examination system; assessing the training that teachers receive in dealing with allergic emergencies; assisting individuals with occupational allergies to return to work. These recommendations therefore need to be taken seriously and acted on, to ensure that patients with allergic rhinitis do not suffer unnecessarily.
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DECLARATIONS
Competing interests JHC is Director of QRESEARCH (a not-for-profit organization owned by the University of Nottingham and EMIS, commercial supplier of computer systems for 60% of GP practices in the UK). JF was a statistician employed at QRESEARCH at the time the work was undertaken. NG, JN and AS have no competing interestsFunding NHS Health and Social Care Information Centre
Ethical approval Not required as this analysis was conducted using only anonymized data
Guarantor JHC
Contributorship AS, JHC and JN were involved in designing the study and NG contributed to literature searches and led the drafting of the paper with all co-authors commenting on drafts of the manuscript
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