Descriptie Epidemiology

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Inflammatory bowel diseases (IBD) are a collection of diseases affecting the bowel, the most common of which are ulcerative colitis and Crohn's disease. Whereas UC is characterised by a continuous distribution of mucosal/submucosal inflammation within the colon, CD may result in focal areas of disease in any part of the gastrointestinal tract from the mouth to the anus; the inflammation is transmural and almost inevitably progresses over time, often leading to structuring or fistulising complications. Extraintestinal complications affecting eyes, skin and joints occur in both illnesses. Although inflammatory bowel disease is not common or highly fatal, it is important to public health because its highest incidence is early in life, its therapy involves major surgery including a curative colectomy for ulcerative colitis, and having the disease increases the risk of developing colon cancer.

There are literally hundreds of articles describing the incidence of ulcerative colitis and Crohn's disease in many regions of the world. In general, the highest incidence rates and prevalence for both diseases have been reported in northern Europe [1-8], the United Kingdom [9-11], and North America [12-15], which are the geographic regions that have been historically associated with IBD. However, reports of increasing incidence and prevalence from other areas of the world such as southern or central Europe [16-18], Asia [19-22], Africa [23], and Latin America [24] underscore the fact that the occurrence of IBD is a dynamic process. Incidence of UC, especially, is rising in several areas previously thought to have low incidence including Japan [21], South Korea [25], Singapore [22], northern India [26] and Latin America [24]. In most of these areas, however, CD remains rare.

In North America, incidence rates range from 2.2 to 14.3 cases/100 000 person-years for UC and from 3.1 to 14.6 cases/100 000 person-years for CD. Prevalence ranges from 37 to 246 cases/100 000 persons for UC and from 26 to 199 cases/100 000 persons for CD [12-14].

The Multicenter European Collaborative Study on Inflammatory Bowel Disease (EC-IBD) reported blended incidence rates between 8.7 and 11.8 cases/100 000 person-years for UC and between 3.9 and 7.0 cases/100 000 person-years for CD [6]. The EC-IBD quantified the north-south gradient of incidence in Europe: the incidence rates for UC and for CD were respectively 40 and 80% higher in northern regions.

City Period Incidence

*100000

Milan 1988-1992 8,8

Florence 1991-1993 9

Reggio Emilia* 1991-1993 8.7

Modcna 1989-1992 3.4

Bologna 1989-1992 3.4

Ave! lino 1989-1992 5.14

L'Aquila 1989-1992 8.5

Messina 1989-1992 7.11

Palermo 1991-1993 10.5

City Period Incidence x100000

Milan 1991-1993 3,4

Florence 1990-1992 3,4

Reygio Emilia 1991-1993 4.3*

Modena 1989-1992 2.4

Bologna 1989-1992 2.4

Ave 1 lino 1989-1992 2.30

L'Aquila 1989-1992 2.4

Messina 1989-1992 1,9

Palermo 1991-1993 6.6*

*agc > 15 yearn Fig. 2. CD incidence rates in Italy ([27])

O 16

vf vf

15-24 25-34 35^14 45-54 55-64 Age groups

15-24 25-34 35^14 45-54 55-64 Age groups

15-24 25-34 35JM 45-54 55-64 Age groups

15-24 25-34 35JM 45-54 55-64 Age groups a b

Fig. 3. a Male and female incidence in different age groups for UC. b Male and female incidence in different age groups for CD ([6])

The last study from northern England [11] suggested that the prevalence of IBD in 1995 was 243/100 000 persons for UC and 144/100 000 persons for CD. Italy, until some years ago, was considered among the countries with low incidence. In Italy, incidence rates are of 5.2 cases/100 000 person-years for UC and 2.3 cases/100 000 person-years for CD (Figs. 1,2) [27].

Incidence per year per lO'inhab.

Male

1413-

b

12-

• 1970-78

109-S-7

A

65

V

b t%2-69

43-

i

2-

0

0

M-29

30-39

40-49

50-59

60-69

> 70 Age in years

Fig. 5. Male annual incidence for UC ([32]

Fig. 5. Male annual incidence for UC ([32]

Female

Incidence per year q per I"1 inhab. * /

lililí 10

7 65

43 20

o 20-29 30-39 4049 50-59 60-69 > 70 Age in years

Fig.4. Female annual incidence for UC ([32])

The northern European studies based on population grounds have shown that there is no increase in overall mortality in IBD [28]. Only in CD has there been an increased mortality observed in the first few years after diagnosis in young patients. In some studies, this was observed primarily in the females. The Italian studies data confirm other European studies [29-31].

In general, there is a slight female predominance in Crohn's disease, especially among women in late adolescence and early adulthood, which suggests that hormonal factors may play a role in disease expression. On the other hand, if there is a slight gender predominance regarding UC, it rests with males [15]. For UC, different patterns of incidence were observed for men and women aged 35 and over, with

M/F

ex-smokers

smokers

all

^^^ ____-

-------------

no-smokers

QUARTTLES

1st 2nd 3rd 4th

QUARTTLES

Fig. 6. Ratio of males to females according to smoking habits and age quartiles ([33])

o 1962-69 "-/'-• 1970-7!

the rates for men remaining fairly constant with increasing age, whereas those for women decreased. Incidence rates for CD were generally lower and were broadly similar for men and women, with rates for both sexes declining with increasing age (Fig. 3) [6].

For UC, a bimodal age distribution for men has been observed: incidence peak in the second and third decades in life followed by a second smaller peak in later decades (over 60 years of age; Figs. 4, 5) [32]. The reason for this bimodal pattern is still unknown. In fact, our study confirms the prevalence of males and the M/F ratio tends to significantly increase with age. The correlation between the age groups and the M/F ratio could be explained by a greater tendency to smoke in men and therefore by a greater, gradual prevalence among them of giving up the habit in relation to, for example, the occurrence of cardiovascular problems (Fig. 6) [33].

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