Epidemiology of In� ammatory Bowel Disease

in Heraklion, Crete

TO THE EDITOR: An article by Farrokhyar et al. (1), publishedrecently in your Journal, raises the question of differentpublished incidence rates for ulcerative colitis (UC) andCrohn disease (CD) in Heraklion, Crete. The relevant � gures(age-standardized incidence rates per 100,000 person-years;standardization according to the European population) of 9.4/105 (2) and 3.3/105 (3), for UC and CD, respectively, do notconcur with the � gures reported in the EC-IBD study, namely19.3/105 for UC and 4.8/105 for CD (4). The Manousos et al.studies (2, 3) included all ages and covered the period 1990–94 (5 years), while the EC-IBD study was restricted to ages15–64 and covered the period 1 October 1991 to 30September 1993 (2 years).

The estimation methods of the incidence rates in (2, 3) andthe numbers of new cases per year were reported in thesearticles, while the population statistics for the study area werereported in (2). Based on these � gures, the results in bothpublications are correct and can be reproduced directly.Furthermore, using these data, the truncated results for ages15–64 are 11.2/105 for UC (95% CI: 8.92–13.43) and 4.2/105

for CD (95% CI: 2.80–5.60). The truncated incidence ratesare therefore increased but remain lower (mainly for UC) thanthose published in the EC-IBD study (4). It appears that thesuggestion of different age bands used in the two studiesmight explain that the difference is not wholly accepted, andFarrokhyar et al. (1) correctly anticipated this.

We reviewed our data for the period 1 October 1991 to 30September 1993 and found two sources of error for the resultsof the EC-IBD study (4) related to Heraklion. The � rst is thepopulation statistics and the second is the number of cases forUC. For example, Table III in (4) shows that 56 new cases ofUC (ages 15–64) were reported for Heraklion during the studyperiod. This was larger than the actual number, which was 51.The population statistics for the various areas were notreported, but the crude rates can be used to � nd the relevant� gures. For example, the total population used for Heraklionmust have been approximately 147,368 (ages 15–64), whichis substantially fewer than the true population of the area forthe same age band, 170,858 (2). In fact, using the actualnumber of cases and the correct population statistics, thecrude rate of UC should be 14.9/105, while the age-standardized rate should be 15.1/105 (95% CI: 10.98–

19.32), which is substantially lower than the rate reported inthe EC-IBD study (19.8/105). It is also higher than thetruncated incidence rate (15–64 years) shown above (11.2/105), but the latter estimate is over a longer period (5 years) inwhich an increasing trend was noted (2).

With respect to CD, the EC-IBD study (4) involved 14 newcases (ages 15–64) for Heraklion during the period 1 October1991 to 30 September 1993. This was the actual number ofcases. Using these data and the population � gures for the area,the crude rate of CD should be 4.1/105, while the age-standardized rate should be 4.06/105 (95% CI: 1.93–6.20).This is similar to the truncated rate shown above (4.2/105).

It seems that an administrative error, not unusual in suchmultidimensional collaborative studies, was responsible forthe different � gures reported for Heraklion in the EC-IBDstudy (4). We are grateful to Farrokhyar et al. (1) for includingthese studies in their review and for identifying thisdiscrepancy.

I. G. Vlachonikolis (correspondence)I. E. KoutroubakisO. N. ManousosFaculty of MedicineUniversity of CreteP.O. Box 1393HeraklionCreteGreeceFax. ‡30 81394606E-mail: socmed@edu.uch.gr

References

1. Farrokhyar F, Swarbrick ET, Irvine EJ. A critical review ofepidemiological studies in in� ammatory bowel disease. Scand JGastroenterol 2001;1:2–15.

2. Manousos ON, Giannadaki E, Mouzas IA, Tzardi M, Koutrou-bakis I, Skordilis P, et al. Ulcerative colitis is as common in Creteas in Northern Europe: a 5-year prospective study. Eur JGastroenterol Hepatol 1996;8:893–8.

3. Manousos ON, Koutroubakis I, Potamianos S, RoussomoustakakiM, Gourtsoyiannis N, Vlachonikolis IG. A prospective epide-miologic study of Crohn’s disease in Heraklion, Crete. Incidenceover a 5-year period. Scand J Gastroenterol 1996;31:599 –603.

4. Shivanada S, Lennard-Jones J, Logan R, Fear N, Price A,Carpenter L, et al. Incidence of in� ammatory bowel diseaseacross Europe: is there a difference between north and south?Results of the European collaboration study on in� ammatorybowel disease (EC-IBD). Gut 1996;39:690–7.

CORRESPONDENCE

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