In this study, we observed a linear increase in the incidence of diagnosed BO in the general population, from 14.3/100 000 person years in 1997 to 23.1/100 000 person years in 2002. If the incidence was based on the number of upper gastrointestinal endoscopies performed in the same period, the increase was even more pronounced, from 19.8/1000 upper gastrointestinal endoscopies in 1997 to 40.5/1000 upper gastrointestinal endoscopies in 2002 (fig 2). The incidence of AC increased in the same period, from 1.7/100 000 to 6.0/100 000 person years.
To our knowledge, only two reports have studied time trends for the incidence of BO at the population level. The conclusions of these studies were conflicting. Prach and colleagues13
showed an increase in incidence from 1.4 new cases of BO per 1000 upper gastrointestinal endoscopies in 1980–1981 to 42.7 new cases of BO per 1000 upper gastrointestinal endoscopies in 1992–1993 in Scotland. They believed their results reflected a true rise in incidence of BO. Conio and colleagues14
also observed a strong increase in the incidence of BO per 100 000 person years in Minnesota but a similar increase in the number of upper gastrointestinal endoscopies was noted over the same time period. They concluded that the increase in incidence of BO in their study reflected a rise in upper gastrointestinal endoscopies performed instead of a true increase in BO.
The main risk factor for BO is gastro-oesophageal reflux disease. The frequency, severity, and duration of acid reflux are positively associated with BO.20,21
It has been estimated that approximately 20% of the general population experience reflux symptoms on at least a weekly basis22
and the incidence of reflux oesophagitis is increasing over time.23
It has been suggested that the incidence of gastro-oesophageal reflux disease is linked with an increasing average body weight,24
and with an increasing average body height in association with a decreasing prevalence of Helicobacter pylori
infection in the population.25
The rise in incidence of BO that we observed was most pronounced in men less than 60 years of age (fig 3). A possible explanation could be that men are now exposed to risk factors for BO at a younger age than they were in the past. Obesity could play a role in this regard. However, obesity at a younger age is also increasing among women, thereby leaving room for other unidentified risk or protective factors for BO.
The observed decline in the number of upper gastrointestinal endoscopies performed per capita in our study is likely to be explained by the introduction of the first general practitioner guidelines on dyspepsia in the Netherlands in 1993, with a revision in 1996.26,27
These guidelines advised restrictions in referrals for upper gastrointestinal endoscopy in the case of dyspepsia in the absence of alarm symptoms.
Incidence studies conducted with computerised medical records have a risk of misclassification. To limit underestimation we used broad search criteria in free text and manually validated all retrieved records. However, pathological reports on the presence of intestinal metaplasia in the BO segment were not available for all BO patients, even after requesting additional information from general practitioners. Restricting our analyses to only histologically confirmed cases did not however change the observed increasing trend over time.
The reliability of our observed number of upper gastrointestinal endoscopies performed is supported by the similar results of a previous nationwide survey by the Dutch Gastroenterology Association, which reported a total of 130 000 upper gastrointestinal endoscopies performed in 2000 in the Netherlands, equalling approximately 8.1/1000 person years.28
As we excluded control and surveillance endoscopies for BO or AC, and also upper gastrointestinal endoscopies performed within three months of the previous one, we feel that our results truly reflect clinical practice in the area under study.
We repeated our analyses including all upper gastrointestinal endoscopies performed within three months of the previous one to assess if this modification changed our results. The incidence of BO per 1000 upper gastrointestinal endoscopies was somewhat lower than in our original analyses but both lines were parallel, indicating a similar increase in incidence of BO over time (data not shown).
It is well known that not all BO patients have reflux symptoms.29–31
As a consequence, most of these patients will not undergo upper gastrointestinal endoscopy and cases will be missed. A study by Cameron and colleagues32
showed a 21-fold higher number of cases of BO based on autopsy findings than was actually seen in the population. This clearly illustrates the magnitude of the potential underestimation of BO in the general population. We assume that such under detection of BO was present in our study also, implying that the actual incidence rate of BO could be considerably higher than that found in our study. However, there is no reason to believe that the degree of this underestimation has changed over time.
The increased incidence of BO over time may partly have resulted from an increased awareness and the improved skills of endoscopists in diagnosing the presence of Barrett’s mucosa. If this is the case, then the observed increase in incidence of BO would, at least in part, be due to a higher detection rate of Barrett’s patients, instead of a real rise in incidence. The distinction between long and short segment Barrett’s might provide further insight as the observer variability is expected to be lower in long segment BO. Unfortunately, such a distinction is not possible in our database. However, the differing trend in incidence between age groups (fig 3) does not support the explanation that the increasing incidence is only secondary to an increased awareness or a change in diagnostic criteria. If increased awareness is solely responsible for the increase in incidence we observed, we would expect similar time trends in the different age groups, and for males and females.
It is likely that the number of patients with AC reported here is underestimated as we excluded patients with oesophageal cancer of unknown type (n
23). Including these patients did not change the trend over time (data not shown). As differentiation between oesophageal cancer and cancer of the gastric cardia, which we did not include, is difficult, it is possible that some additional cases were missed.
Estimates for the incidence of AC were based on small numbers and had wide confidence intervals. Despite the fact that chance may explain at least some of our results, another study in the Netherlands, based on the Dutch Cancer Registry, showed an increase of similar magnitude in the incidence of AC over a six year period preceding our study (1990–1996).33
It seems that the increase in incidence of AC between 1997 and 2002 was greater than the increase in incidence of BO over the same period. As it is generally expected that progression from BO to AC takes several years, it may be that the incidence trend for AC in this study reflects the incidence trend for BO from several years ago and the increase in incidence of BO is slowing down at present. It is also possible that the rising incidence of BO is not solely responsible for the increase in incidence of AC. Other factors may also be important such as those influencing the rate of malignant progression from BO to AC.
In conclusion, our results showed an increase in the incidence of detected BO, which cannot be explained by a rise in the number of upper gastrointestinal endoscopies performed. The cause of this increase and its implications require further study but it is likely that a further increase in the incidence of BO carcinomas in the coming decade will occur.