In a large population with an almost negligible growth rate and minimal migration, the incidence of type 2 diabetes mellitus is 3 cases per 1,000 individuals a year, and has been stable for the last 30 years. However, the prevalence of type 2 diabetes mellitus has increased progressively over the same period. Which of the following is the most likely explanation for this trend over time?

Question

In a large population with an almost negligible growth rate and minimal migration, the incidence of type 2 diabetes mellitus is 3 cases per 1,000 individuals a year, and has been stable for the last 30 years.  However, the prevalence of type 2 diabetes mellitus has increased progressively over the same period.  Which of the following is the most likely explanation for this trend over time?

Quizplus · Accepted Answer

Explanation: Incidence and prevalence are 2 important concepts in epidemiology that measure disease occurrence in a population: Incidence and prevalence Incidence (incident cases) refers to the number of new cases of disease that develop in a specific population over a specified time period. By contrast, prevalence quantifies existing cases of disease in the population at a particular point in time. Prevalence of disease depends on how fast cases develop and on the duration of the disease. When a population has reached a stable condition, as suggested by a negligible growth rate (ie, neither growing nor shrinking in size) and minimal migration, the prevalence of disease can be approximated by considering the incidence and the duration of disease in the following manner: Prevalence = (Incidence) × (Duration of disease) In this case, the specific population has a rising prevalence but a stable incidence of diabetes. In other words, more people are being documented as having diabetes although the number of people being newly diagnosed each year remains the same. Because incidence is stable, the increasing prevalence can likely be attributed to factors that prolong the duration of the disease, such as improvements in quality of care and disease management, which may lead to a significant increase in life expectancy. (Choice A) Decreased length of hospital stay is not helpful in explaining the increased prevalence described in this case. (Choice B) A high mortality rate in patients diagnosed with type 2 diabetes mellitus would result in a decrease, rather than an increase, in prevalence. (Choice D) Increased diagnostic accuracy would significantly increase both incidence and prevalence of disease. (Choice E) Selective survival bias refers to the selection process of prevalent cases rather than incident cases in a case-control study. Educational objective: An increasing prevalence but stable incidence of a disease can be attributed to factors that prolong the duration of the disease (eg, improved quality of care and disease management).

In a Large Population with an Almost Negligible Growth Rate