The current study estimates prevalence of diagnosed common diseases in the total population in Stockholm County, a region with more than 2 million inhabitants, using recorded diagnoses in regional registers. The high prevalence of the six common diagnosis groups reported in this study calls for preventive action to be taken. Still, there may be people who are not yet diagnosed and population based health assessments have yielded individuals with newly diagnosed hypertension and diabetes [1, 14]. With more than 30% of men and 20% of women aged between 75–84 years being diagnosed with diabetes during a five-year period, considerable amounts of health care resources will be needed. In addition, with 55% of all men and women in this age-group being diagnosed with hypertension, a considerable burden could be expected as this group would likely develop cardiovascular complications. The large amounts of younger patients diagnosed with these conditions, subsequently developing complications, may also pose a challenge for the future.
The fact that the population is large enables stratification by sex and age. Bearing in mind that approximately 20% of the inhabitants of Stockholm County are immigrants , the prevalence of common diseases in an urban population of a Western country can be used as a proxy for the prevalence of these diagnosed diseases in similar populations of other regions or countries.
The overall prevalence of diagnosed COPD was 1.8%, which was higher than a previous study of COPD prevalence in a population living in a rural region of Sweden (1.2%) that had a similar design . The difference in prevalence could be due to more particles in the air in Stockholm, higher proportion of smokers or a higher awareness of COPD in recent years. Prevalence of diagnosed COPD increased dramatically among persons aged between 45–84 years whereas it decreased among persons aged 85 years and over which may be explained by the effect of smoking on longevity . The opposite was observed for the prevalence of anxiety /phobia which was high in young adults aged between 18–44 years (6.6%). A recent Swedish study, where a population based sample of 75-year-old persons was interviewed over a period of one month, reported that 3.7% had generalized anxiety disorder according to ICD-10 , which is consistent with the five-year prevalence of 4.2% among persons aged between 65–74 years of the total population of Stockholm County reported in this study. Another Swedish study reported that as much as 24% of the Swedish population aged 20–64 years fulfilled the criteria for anxiety and/or depression .
Diabetes is often regarded as equally common among men and women, although a male preponderance has been observed in those aged 45 years and over . Wirehn et al. (2007) found an overall male preponderance in diagnosed diabetes prevalence (4.6% in men vs 4.1% in women)  while in the current study an even larger male predominance in diagnosed diabetes prevalence was found (7.1% in men vs 5.3% in women). In a review (2001), Gale and Gillespie concluded that men may be more susceptible to physical inactivity and obesity than are women . Overall prevalence of diagnosed diabetes was higher in the current study (6.2%) than in earlier studies in Sweden (4.5%) [7, 21]. One explanation for the discrepancy may be the higher rate of immigrants living in Stockholm County . A population-based study has shown that two thirds of the 60-year old diabetes patients are known .
The five-year period prevalence of diagnosed depression was high among adults, ranging between 9.0% and 12.2% in women and between 4.7 and 7.9% in men. The higher prevalence of depression among women than among men has been reported previously , and may be due to that women may be more active in seeking health care when they experience depressive symptoms. Also, the prevalence of diagnosed depression was lower among individuals younger than 65 years of age than those aged between 65–74 years which may be explained by lack of incentive to be sick-listed in the years following retirement. Persons with depression have been shown to have a higher risk for somatic diseases than non-depressed individuals , which may have had an effect on the diagnosed prevalence of all diagnosis groups in women in this study.
Studies of hypertension in the US have shown that the prevalence in the adult population (18 years of age and over) was nearly 30% [25, 26], which was higher than that we reported in this study (12.2%) implying there may be a large number of undiagnosed individuals in the total population of Stockholm County. This is in agreement with a screening study of 60 year-old persons from Stockholm which showed that newly diagnosed hypertension was more prevalent than already diagnosed hypertension . The prevalence of hypertension is highly dependent on age , which was consistent with our findings. It has been previously shown that prevalence of hypertension is lower in women than in men until menopause, after which prevalence increases and reach levels observed in men [28, 29]. Large scale population-based investigations are, however, still sparse and the true prevalence in the population is therefore not fully known, making the findings of the current valuable. Moreover, hypertension awareness, treatment and control vary greatly in different studies from around the world , and in populations of different countries studied following the same methodology .
In contrast to the other diagnosis groups, asthma appeared to affect children the most. Furthermore, diagnosed asthma was more common in boys than in girls and in women than men. The prevalence rates and gender differences are consistent with a recent review estimating the overall prevalence of asthma at 5-7% in the total population and 8-10% in children . Previous studies have also shown that women with asthma seek care more often than do men [33, 34]. Asthma in children is often associated with rhinitis and eczema as well. The BAMSE birth cohort reported that 58% of 12 year-old children had one, two or all these three conditions at some time .
Our study revealed important information on the prevalence of diagnosed common diseases in the population. It could be useful for the planning of healthcare needs, resource allocation and disease prevention. Access to electronic longitudinal data from primary healthcare may also provide unique opportunities for performing post-marketing comparative effectiveness research . Some benefits include availability of large populations at a relatively low cost and shortening the time necessary to identify a sufficient number of patients with a specific diagnosed disease. They may also enable studies of patient groups that are usually omitted from randomized controlled trials, i.e. patients with co-morbidities . Recently, prescription data on individuals, using the same encrypted identification numbers as data from VAL, have been added to the database. This enables a unique possibility to link drug prescriptions to diagnoses and patient outcome.
It is important to emphasize that the frequency and diagnosis coverage may vary between different physicians, primary health care centres and diagnosis group . Additionally, the reporting of diagnoses may change along with changes in the healthcare reimbursement system, however, no major changes occurred in the region during the course of this study. To achieve better prevalence estimates, data from PC, SOC and IC could be used together and from consecutive years . The applicability of our method may also vary between different settings. Health care systems vary widely across different regions and countries. More patients in Stockholm receive their care from specialists other than GPs, due to an proportionally smaller primary care sector compared with the UK .
Inclusion of only those who were alive at the end of the study period has likely introduced a survival bias as individuals who died during the five-year period were likely to have used considerably more healthcare resources than average. Consequently, the prevalence of diseases that are common among older persons, such as COPD, may have been underestimated. However, this is not a problem if the data are interpreted as point prevalences.
Most of the conditions encountered in PC are readily treatable, for example acute infections and inflammatory conditions, whereas others are chronic or relapsing and often non-acute such as diabetes mellitus, depression, anxiety disorders, hypertension, asthma, and chronic obstructive pulmonary disease (COPD). The diagnostic accuracy may also vary, depending on the disorder and the diagnostic criteria applied. For diabetes, highly valid diagnostic criteria make the disease easy to identify . In the current study we did not make a distinction between Type I and Type II diabetes, as one of the most commonly used diagnosis codes in primary care is diabetes mellitus not otherwise specified. However, it is well known than Type II diabetes is more prevalent than Type I diabetes. While data on asthma, hypertension and diabetes diagnoses the diagnostic accuracy could be expected to be of high validity, data on COPD, anxiety/phobia, and depression may not be as straightforward.
Stockholm County has seen more people moving in than moving out. Consequently, a slight underestimation in prevalence of the diagnostic groups may be expected as new inhabitants may have not yet lived in Stockholm long enough to have diagnoses recorded during the five-year period of interest. This may hold true for individuals aged between 18–44 years. However, this effect may have been balanced out by excluding those who died during the same period.