Multimorbidity Epidemiology

Reviewed by Dr. Liji Thomas, MD

Multimorbidity is defined as the existence of two or more long-term chronic illnesses in the same individual at the same time. Usually neither of the medical conditions is considered dominant – instead, the conditions exist alongside one another, each having a significant impact on the patient.

This phenomenon is increasingly common in the population today and is strongly linked to age, sex and the socio-economic status. Some of the most common disorders that cause multimorbidity include: hypertension, depression and anxiety, and chronic pain.

Multimorbidity. Image Credit: WHO

Relation to Age and Sex

Most studies show a positive correlation between the prevalence of multimorbidity and age, although it affects patients of all age groups. It is most widespread in those over the age of 50 and as such, it is becoming a growing issue in today’s aging population.

In one Dutch study, approximately 10% of patients under the age of 15 were known to their GP as having at least one chronic disease. However, this percentage increased to over 90% in patients over the age of 75. Interestingly though, comorbidity of physical-mental conditions is most prevalent in younger patients (between 18-44 years old) and poorer patients.

Multimorbidity also shows strong positive linkages to sex and it is more common among females according to most studies. However, research performed in New Zealand has shown that multiple chronic illnesses are more common among males according to hospital data, although data based on pharmaceutical dispensing still shows a higher prevalence among females.

Relation to the Socio-Economic Status

The prevalence of multimorbidity depends strongly on the socio-economic class. It is more common in lower socio-economic strata, which is in turn is associated with the frequency of use of health services by the patient. Long-term conditions seen in the socioeconomically disadvantaged are linked to a greater exposure to social, environmental or workplace risk factors, as well as certain risk factors at an individual level, such as smoking, poor diet, lack of exercise and poverty of access to healthcare. In contrast, patients in a high socio-economic class are more likely to have no chronic illnesses at all.

The increased need for use of healthcare services by patients suffering from two or more chronic illnesses is particularly evident when considering the primary healthcare system. In the UK, patients with multimorbidity account for over a half of GP consultations and hospital admissions. What is more, over three quarters of the total number of prescriptions dispensed annually are administered to patients suffering from a number of chronic illnesses who consequently need access to a number of medications.

A rise in the effectiveness of treatment offered and the patients’ survival rates means an increase in the prevalence of chronic diseases. In the developed nations, where the life expectancy is growing, the incidence of multimorbidity is set to increase as well. This is in contrast to the less developed countries, where a greater number of patients suffer from acute illnesses as compared to the numbers recorded in most developed nations.

Limitations of Epidemiology Research

While most research to assess the prevalence of multimorbidity in today’s population is performed on a large pool of participants, the data in each study is mostly limited by being collected in one country. Furthermore, the list of chronic illnesses assessed in each study varies, with some considering as many as 75 long-term illnesses for the purpose of the study.

Some research groups take additional steps to consider sets of three or four chronic conditions that frequently occur together and perform separate data analysis of these, obtaining interesting results which may vary from those obtained with a larger sample size.

Similarly, studies may be limited to a smaller age group in order to assess the prevalence of multimorbidity in the younger population only. As such, the percentage of the population with multimorbidity can vary significantly depending on the data set used. For example, one study performed among the Swiss population found a multimorbidity prevalence of between 13.0% and 76.6%, depending on the chronic conditions considered, the data used and the population covered. Another factor to consider is the increase in the prevalence of chronic diseases as a result of heightened public attention to chronic diseases.

Further Reading

• All Multimorbidity Content
• Multimorbidity Treatment Challenges
• What is a Concomitant Illness?