NUR 603 Module 2 Short Paper Example

Fewer New Cases, the Same Number Living With It: Reading US Diabetes Incidence and Prevalence Together

[Student Name]

Southern New Hampshire University

NUR 603: Epidemiology

Module Two Short Paper

[Instructor Name]

[Date]

Fewer New Cases, the Same Number Living With It: Reading US Diabetes Incidence and Prevalence Together

A headline announcing that diabetes is declining in the United States and another announcing that it remains at record levels can both be accurate. The difference lies in which measure each one reports. Incidence counts people who newly develop a condition during a stated interval; prevalence counts everyone who has the condition at a given moment, new or long-standing. This paper uses national data on diagnosed diabetes to show how the two measures can move in different directions and argues that reading them together, along with what is known about duration and diagnosis, gives a more honest picture than either one alone.

Defining the Measures

Incidence is a rate of new events. For diagnosed diabetes, it is the number of adults newly told they have diabetes in a year divided by the number of adults at risk, meaning those without diagnosed diabetes at the start of the year, and it is often expressed per 1,000 persons per year. Prevalence is a proportion. It is the number of adults living with diagnosed diabetes at a given time divided by all adults in the population, usually expressed per 100. Incidence tells us about risk and the effect of prevention; prevalence tells us about burden and the need for services. Both require a stated population, a stated time frame and a stated case definition, which here is self-reported diagnosis by a health professional in a national household survey.

What the Data Show

Benoit et al. (2019) calculated age-adjusted incidence and prevalence of diagnosed diabetes among civilian, noninstitutionalized adults aged 18 to 79 from the National Health Interview Survey for 1980 through 2017. Table 1 summarizes their main findings. Both measures were flat during the 1980s and rose steeply from 1990. Then they parted. Incidence peaked in 2007 and declined by about 3.1% a year to 2017, a decrease driven mainly by non-Hispanic White adults. Prevalence peaked in 2009 and plateaued rather than falling.

Table 1. Age-Adjusted Diagnosed Diabetes Among US Adults Aged 18 to 79

Note. Data from the National Health Interview Survey as analyzed by Benoit et al. (2019). Values are age adjusted.

Why Prevalence Can Hold as Incidence Falls

In a population in steady state, prevalence is approximately equal to incidence multiplied by the average duration of disease. Duration for a chronic condition like diabetes is ended mainly by death. If incidence falls while duration lengthens, the two changes can offset each other, and prevalence can stay level for years. Prevalence will begin to fall only when the smaller number of new cases no longer replaces those who die.

A rough calculation shows how closely the national figures fit this relation. Converting both measures to the same units, an incidence of 6 new diagnoses per 1,000 adults per year is 0.6 per 100 per year. If the average person diagnosed lived with diabetes for about 14 years, prevalence would be about 0.6 multiplied by 14, or 8.4 per 100, very close to the observed plateau of 8.2. The calculation is only illustrative, since the population is not truly in steady state and survival differs by age at diagnosis, but it shows that a modest lengthening of duration can hold prevalence level while incidence falls by a quarter.

There is good evidence that duration has lengthened. In linked national survey and death records, death rates among men with diagnosed diabetes fell from 40.7 to 27.8 per 1,000 person-years and among women from 42.7 to 29.5, declines of about a third, driven largely by fewer deaths from vascular disease (Gregg et al., 2018). Longer survival is good news, but it keeps prevalence high even as fewer people develop the disease.

Could the Change Be an Artifact?

Before accepting that fewer people are developing diabetes, a change in diagnosis or detection must be considered. In 2009, an international expert committee recommended hemoglobin A1c as a diagnostic test (International Expert Committee, 2009), and its adoption in 2010 changed how diabetes was identified in practice. A shift in tests could change who is diagnosed and when, which would move diagnosed incidence without any change in underlying disease. The timing does not fit neatly, since incidence had begun falling before the change, but it may contribute.

Undiagnosed diabetes also matters, because both measures here count only diagnosed cases. Using laboratory data from national examination surveys and a confirmatory definition, Selvin et al. (2017) found that undiagnosed diabetes fell from 16.3% of all diabetes cases in 1988 to 1994 to 10.9% in 2011 to 2014. Better detection earlier in the period could have raised diagnosed incidence temporarily, as a backlog of existing cases was found, and a later decline could partly reflect the end of that backlog rather than lower risk.

What This Means for Practice

The falling incidence is encouraging for prevention, though the decline was concentrated in one group, which means prevention has not reached everyone equally. The steady prevalence tells a clinic to plan for a stable or growing number of patients living with diabetes and aging with it, who will need management of kidney disease, neuropathy and the cancers and dementia that now account for a larger share of deaths in this group (Gregg et al., 2018). A nurse practitioner reading only the incidence headline might underestimate the need for chronic care; one reading only the prevalence headline might miss that prevention is working for some. Both readings would lead to poorer planning, which is why a population profile for a clinic or county should report the two measures together, stratified by age and by group.

Conclusion

Diagnosed diabetes incidence in the United States fell for a decade while prevalence held steady. The main reason is that people with diabetes are living longer, with possible contributions from changes in diagnosis and the finding of previously undiagnosed cases. Reading incidence and prevalence together, with their denominators, time frames and case definitions stated, shows both the progress and the continuing burden.

References

Benoit, S. R., Hora, I., Albright, A. L., & Gregg, E. W. (2019). New directions in incidence and prevalence of diagnosed diabetes in the USA. BMJ Open Diabetes Research & Care, 7(1), Article e000657. https://doi.org/10.1136/bmjdrc-2019-000657

Gregg, E. W., Cheng, Y. J., Srinivasan, M., Lin, J., Geiss, L. S., Albright, A. L., & Imperatore, G. (2018). Trends in cause-specific mortality among adults with and without diagnosed diabetes in the USA: An epidemiological analysis of linked national survey and vital statistics data. The Lancet, 391(10138), 2430-2440. https://doi.org/10.1016/S0140-6736(18)30314-3

International Expert Committee. (2009). International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care, 32(7), 1327-1334. https://doi.org/10.2337/dc09-9033

Selvin, E., Wang, D., Lee, A. K., Bergenstal, R. M., & Coresh, J. (2017). Identifying trends in undiagnosed diabetes in U.S. adults by using a confirmatory definition: A cross-sectional study. Annals of Internal Medicine, 167(11), 769-776. https://doi.org/10.7326/M17-1272