Epidemiology is the study of disease patterns in a population. It tends to look for trends in disease progression, and for clusters of activity on a meta level. Epidemiological studies are good for identifying environmental causes of disease, geographic or racial predispositions, and correlative information that can focus future studies on finding root cause. For those of us suffering from IBD, the numbers from these studies also provide information on how prevalent the disease is and what the progression will probabilistically look like.
Overall, the current incidence of IBD is as follows:
- Ulcerative Colitis: 0.5–24.5 per 100,000 persons
- Crohn’s Disease: 0.1–16 per 100,000 persons(1)
Aggregating and averaging the numbers (which will be shown below not to be a very good representation, except for global comparison to other diseases), approximately one out of every 5,000 people globally are diagnosed with IBD. It is hard to pin down incidence rates to an exact number due to varying standards of care globally, lack of consistent diagnosis (IBD is frequently misdiagnosed as Irritable Bowel Syndrome or general gastroenteritis upon presentation of the initial symptoms and later refined), and lack of data in many regions. Additionally, because IBD generally presents itself between the ages of 15 and 35, areas with very low life expectancies and a history of other gastrointestinal illnesses may have underrepresented numbers (i.e. if you die of cholera or amoebic dysentery at 25, it may never be known if you had concomitant IBD).
Certain populations definitely have higher rates of IBD than others. In general, the following are significantly more likely to have diagnosed IBD based on current data:
- Caucasians, specifically those of Northern and Western European decent.
- Females (only with Crohn’s and only to a small degree)
- Individuals living in urban areas.
- Individuals with a blood relative (especially a sibling) with IBD.
The incidence of IBD in most of Southeast Asia is very low, though the rate of increase is fairly high. In the US, the combined prevalence is approximately 5 people per 1,000. It has been postulated that this may be due to a change in diet or lifestyle, though the introduction of a pathogen that favors of other climates or genetic mixing cannot be ruled out. To further complicate things, it may be a multifactor issue – a genetic predisposition in an individual that comes into contact with a specific pathogen (or class of pathogens) that flourishes due to a particular lifestyle (though it would be nice to be reductionist and find a single cause).(2)
The other side of epidemiology of interest to those with IBD focuses on disease progression and outcomes. One question everyone has when first diagnosed is what is the prognosis? There will be a definite impact to quality of life, but the impact on quantity of life is difficult to determine. There are a few studies that have looked at this, however, that can shed some light on the statistical probability in these areas.
In terms of progression, “complicated” disease is defined by the introduction of irreversible tissue damage. Standard inflammation can go down with treatment or time, and the tissue can repair itself. Lesions that form scar tissue, however, don’t self-repair. Strictures and fistulae are representative of complicated disease that requires surgery or aggressive medication therapy to treat properly. Complicated disease can present at any time (I was initially diagnosed with Crohn’s after my first fistulotomy), and in some patients it never progresses beyond the early disease stages. Complicated disease stats for Crohn’s are as follows:
- At Diagnosis: 19-38%
- After 10 years: 56-65%
- After 20 years: 61-88%(3)
For both Crohn’s and Ulcerative Colitis, the age of onset plays a major factor in disease progression. Those diagnosed at an earlier age show a more rapid progression to complicated disease.(4) Additionally, the trends toward complicated disease are moving in a good direction – preliminary studies are showing that early diagnosis and more aggressive treatment may delay or stave off the onset of complicated disease. Therapeutically this is ascribed to immunomodulators, and may look even better once the new generation biological have been in use for an extended period. (5,6)
In terms of impact on overall lifespan, the measurement used is standardized mortality ratio, or SMR. For Ulcerative Colitis, the SMR is close to 1.0, which means that the number of deaths in UC patients compared to the normal population in a given period of time is the same. For Crohn’s disease, the SMR is approximately 1.4, which means those with Crohn’s disease have 40% more deaths when compared to the normal population in a given period of time. In general, the effects are on the overall mortality – in terms of the number of individuals that die directly from the disease (e.g. due to toxic megacolon or similar complications), the numbers are 1-3% of sufferers. Overall, those with hospitalizations and surgeries under their belt for IBD (and therefore complicated disease) have a higher SMR. (7)
*Note the difference between incidence and prevalence above. Incidence is the rate of occurrence of the disease (number of cases that occur over a period of time) – prevalence is the total population. Incidence shows if a disease is become more or less common and changes with treatment. Prevalence shows the total number of people impacted at any given point.
- IBD is on the rise everywhere, though better diagnoses and other factors may contribute to this rise.
- Approximately 5 per 1,000 people in the US have IBD.
- Crohn’s disease patients, especially those with complicated disease, have a statically lower life expectancy. UC patients generally do not have a statistically lower life expectancy.
(1) Loftus EV. Clinical epidemiology of inflammatory bowel disease: incidence, prevalence, and environmental influences. Gastro May 2004.
(2) Michael Economou, MD, PhD, Georgios Pappas, MD. New Global Map of Crohn’s Disease: Genetic, Environmental and Socioeconomic Correlations. Inflammatory Bowel Disease, 2007.
(3) Edouard Louis. Epidemiology of the Transition from Early to Late Crohn’s Disease. Digestive Diseases, 2012
(4) Corinne Gower-Rousseau, Francis Vasseura, Mathurin Fumery, Guillaume Savoye, Julia Salleron, Luc Dauchet, Dominique Turck, Antoine Cortot, Laurent Peyrin-Biroulet, Jean Frédéric Colombel. Epidemiology of inflammatory bowel diseases: New insights from a French population-based registry (EPIMAD). Digestive and Liver Disease, 2012.
(5) Barbara D. Lovasz, Petra A. Golovics, Zsuzsanna Vegh, Peter L. Lakatos. New trends in inflammatory bowel disease epidemiology and disease course in Eastern Europe. Digestive and Liver Disease, 2012.
(6) Charles N Bernstein, Edward V Loftus Jr, Siew C Ng, Peter L Lakatos, Bjorn Moum. Hospitalisations and surgery in Crohn's disease. GUT 2011.
(7) Christian P. Selinger MBBS, MRCP, Rupert W. Leong MBBS, FRACP, MD. Mortality from inflammatory bowel diseases. Inflammatory Bowel Disease, 2012.