Original Articles
Multimorbidity in General Practice: Prevalence, Incidence, and Determinants of Co-Occurring Chronic and Recurrent Diseases

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Abstract

Increasing numbers of people are found to have two or more diseases at the same time, which is termed multimorbidity. We studied the prevalence, incidence, and determinants of multimorbidity and the statistical clustering of chronic and recurrent diseases in a general practice setting. Prevalence of multimorbidity increased with all age groups from 10% in the 0–19-year-old age group up to 78% in subjects aged 80 and over. Increasing age, lower level of education, and public health insurance were related to the occurrence of morbidity, but even more strongly to the occurrence and degree of multimorbidity. The one-year incidence of multimorbidity (the new occurrence of two or more diseases in one year) was related to increasing age, public health insurance, and the presence of prevalent diseases at baseline. Statistical clustering of diseases was stronger than expected, especially among the younger subjects.

Introduction

During the last few decades the prevalence of chronic medical conditions has risen because of increased longevity [1]. As a result of the growing proportion of elderly people in the community, the prevalence of chronic conditions is expected to rise further. Moreover, it is becoming increasingly common for patients to have two or more medical conditions at the same time. A specific combination of diseases or additional diseases beyond the index disease under study is called comorbidity, while any co-occurrence of diseases is termed multimorbidity [2]. For a patient, multimorbidity may have profound implications. The degree of physical and social disability rises with the number of a patient's medical conditions 3, 4, 5. Multimorbidity also has an impact on family and friends [1]: caring may take a lot of time and physical and emotional energy; and sometimes a considerable change in lifestyle is needed [6]. Multimorbidity often requires complex therapy and care, which demands special attention, knowledge, and skills of the medical attendants and nurses. For society, multimorbidity causes an increased need for social, medical, and health care services and a loss of productivity.

Previous studies on multimorbidity reported two or more medical conditions at the same time in 3.6% [7] to over 50% [3] of the populations under study. Comparing these studies is difficult because of the many differences in methodology, population, and number and type of diseases under study. It is clear, however, that the number of co-existing diseases in a person rises with age 1, 3, 7, 8. Other determinants of multimorbidity have not been studied extensively, and research on the determinants of co-occurring diseases using a broad nosological spectrum is especially rare. Most of the existing research has concentrated on studying a small number of diseases in a restricted population: for example, only elderly people or only patients admitted to hospital. Therefore, it is difficult to draw more general conclusions from these studies. Because of the serious consequences of multimorbidity for the patient, family and friends, and society, it is important to gain more insight into the occurrence and the determinants of multimorbidity.

In this article we report on the prevalence and incidence of multimorbidity in a Dutch general practice population. Multimorbidity is especially relevant in general practice; whereas most clinical specialities focus on one or more organ systems, the general practitioner (GP) encounters a much broader spectrum of medical conditions. As a result, general practice is a very appropriate setting to study multimorbidity. In the Netherlands all people are registered in a general practice. General practitioners deliver continuous care to their patients, and they are the gate-keepers to the other health care facilities. After referral, all results are reported to them. As a result, general practitioners have comprehensive information on the health status of their patients.

The current study uses a broad nosological spectrum classified within a large number of separate medical conditions. There were no limitations regarding age, use of health care services, or presence or absence of certain diseases. In fact, since in the Netherlands all individuals are registered in a general practice, the epidemiological denominator represented the general population. The influence of basic sociodemographic characteristics on the occurrence of multimorbidity was evaluated. By gaining insight into these relations we aim to trace determinants of susceptibility to disease in general and to be able to identify vulnerable groups.

Finally, we studied the statistical clustering of diseases in our study population. The observed number of diseases within patients was compared to the statistically expected number (assuming independence) and tested for significant differences. In this study we did not focus on specific combinations of diseases, our main goal being to examine whether or not diseases cluster within persons.

Section snippets

Context

This study was carried out within the context of the Registration Network Family Practices (RegistratieNet Huisartspraktijken, RNH). This is a continuous and computerized database in which 42 general practitioners, working in 15 different practices in the south of the Netherlands, are participating. All relevant health problems are registered. A health problem is defined as “anything that has required, does or may require health-care management and has affected or could significantly affect a

Prevalence

Overall, multimorbidity (two or more diseases at the same time) was found in 29.7% of the registered subjects. The mean number of prevalent diseases was 1.21 (95% CI 1.19–1.22) and varied from 0.46 in the youngest females to 3.57 in females aged 80 years and older, and from 0.51 in the youngest males to 3.24 in the oldest males. A higher prevalence of multimorbidity was found among the elderly (chi-square test for trend, P < .0001); among women (chi-square, P < .0001) (Table 2); and among

Discussion

Our analysis showed that multimorbidity—the co-occurrence of two or more chronic or recurrent diseases within one person—is a common phenomenon with a prevalence of 29.7% in our study population, ranging from 10% in the 0–19-year-old age group to 78% in subjects aged 80 and older. Most other studies have reported a lower prevalence 3, 4, 7, 14, which can be explained by the limited number of conditions included in those studies. Parkerson [15] is the only one who found a higher overall

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