What Is Known
The incidence of paediatric inflammatory bowel disease is increasing globally.
There is a relative paucity of epidemiological data from the Southern Hemisphere.
Recent data have shown a relatively high point prevalence of paediatric inflammatory bowel disease in New Zealand .
What Is New
The prospectively calculated, national, incidence rates of paediatric inflammatory bowel disease and its subtypes in New Zealand are among the highest in the literature.
The incidence rates of paediatric inflammatory bowel disease in New Zealand have nearly doubled in 12 years.
The inflammatory bowel diseases (IBD) are chronic conditions with significant impact on the health infrastructure of a country (1) paediatric population (2) incidence of paediatric IBD is on the rise (3) paediatric IBD from the Southern Hemisphere when compared to North America and Europe (4–14)
A previous study demonstrated that the Canterbury region in New Zealand had one of the highest rates of Crohn disease (CD) in the world (15) (16) paediatric IBD in New Zealand was conducted between 2002 and 2003 and concluded that the incidence of paediatric IBD was at the lower end of incidence rates reported from other Western countries (17) incidence of both CD and ulcerative colitis (UC) over the last few decades (18,19)
It was hypothesised that the incidence of paediatric IBD in New Zealand was comparable to other countries of similar socioeconomic standing in the world. The Paediatric Inflammatory Bowel Disease in New Zealand (PINZ) study was established in 2015 to prospectively follow every child in the country ages 16 years and younger who was newly diagnosed with IBD. This report ascertains the incidence of paediatric IBD in NZ for the calendar year 2015.
METHODS
Approval for the PINZ study was obtained from the Health and Disability Ethics Committee (HDEC) of the Ministry of Health of New Zealand .
Study Population
The inclusion criteria for this study consisted of having a diagnosis of IBD (according to widely accepted criteria (20,21) New Zealand . Relevant details on each patient were entered into a secure Microsoft Access database (Microsoft Office Professional Plus 2013, Redmond, WA).
Specific details that were collected and recorded included date of birth, sex, ethnicity, address, year of IBD diagnosis, diagnostic modalities employed, most severe disease phenotype (classified according to the Paris modification of the Montreal classification system (22)
In the case of family history, the affected person's degree of kinship with the patient was noted. Where more than 1 family member was affected by IBD, the closest degree of kinship was noted. Rheumatological involvement consisted of nonspecific IBD-related arthritis. Dermatological involvement consisted of erythema nodosum. Hepatobiliary involvement included autoimmune hepatitis and primary sclerosing cholangitis. Orofacial involvement was considered in this study for cases with mouth ulcers, angular cheilitis, and orofacial granulomatosis (with intestinal IBD); orofacial granulomatosis patients without intestinal inflammation were excluded from the PINZ study.
The ethnic group classifications used in this study are in keeping with the recognized major ethnic groups in New Zealand , namely European, Mãori, Asian, Pacific peoples, and Middle Eastern/Latin American/African (23)
New Zealand Situated in the South Pacific between 34° and 47° latitude south, with a land mass similar to that of the United Kingdom, New Zealand is made up of the North Island and the South Island (24) New Zealand 's estimated resident population was 4.6 million (24) (24)
Case Recruitment
Information on every paediatric patient with IBD in the South Island has been prospectively collected by one of the authors (A.S.D.). New diagnoses of IBD made between 1 January 2015 and 31 December 2015, were also concurrently entered into the PINZ database.
Starship Children 's hospital in Auckland provides paediatric gastroenterology care to all children with IBD in the North Island younger than 16 years either at the hospital or at outreach clinics held throughout the North Island. Each of the 4 Starship Hospital paediatric gastroenterologists prospectively notified one of the authors (R.N.L.) of every patient who was diagnosed with IBD between 1 January 2015 and 31 December 2015 These notifications comprised patients resident in Auckland and those who lived in other North Island locations.
Members of the New Zealand Society of Gastroenterology, which represents at least 95% of practising gastroenterologists in the country, were made aware of the PINZ study and invited to approach the authors if they had patients who met the study criteria. Further to that, key clinicians working in 2 of the biggest private adult gastroenterology practices in Auckland and gastroenterologists with significant private practices in Wellington, Christchurch, and the Hutt Valley were individually approached about potential patients meeting inclusion criteria for the current PINZ study. It was thought highly unlikely, following discussion between the authors of this work, that any other centres in the country would likely have children with IBD cared for exclusively in the private sector.
In every instance, electronic patient records were studied. Where there was any ambiguity, the hard-copy case notes were retrieved to ensure accuracy of data collection.
Data Analysis
The last New Zealand census was performed in 2013 by Statistics New Zealand . In years in which no census is undertaken, estimated population data are made available. The estimated New Zealand population of people between 0 and 15 years of age on 30 June 2015 was obtained from Statistics New Zealand (personal communication) for the purposes of the present study. These figures were broken down by age range, sex, and geographic region.
The incidence of paediatric IBD in New Zealand between 1 January and 31 December 2015 was calculated for IBD, CD, UC, and IBDU with the number of new diagnoses serving as the numerator and the population estimate for that year serving as the denominator. Rates are reported per 100,000 population.
All raw data were analysed descriptively. Age ranges are given as median with relevant interquartile ranges (IQRs). Categorical variables were compared using either the unpaired t test or 1-way analysis of variance. Statistical significance was accepted if P < 0.05. Most of the statistical analyses was performed using GraphPad Prism version 6.00 (GraphPad Software, LaJolla, CA) except for the calculations of the 95% confidence intervals (CIs) of the incidence rates which were analysed using OpenEpi: Open Source Epidemiologic Statistics for Public Health, Version. (www.OpenEpi.com
RESULTS
Incidence of Paediatric Inflammatory Bowel Disease in New Zealand in 2015Between January 1, 2015 and December 31, 2015, 51 children younger than 16 years were diagnosed with IBD in New Zealand . Thirty-four (66.7%) had CD, 10 (19.6%) UC, and 7 (13.7%) IBDU.
The prospectively calculated national incidence of paediatric IBD in 2015 was 5.2 of 100,000 (95% CI 3.9–6.8) people younger than 16 years (Table 1 ). The incidence of CD, UC, and IBDU, respectively was 3.5/100,000 (95% CI 2.4–4.8), 1.0/100,000 (95% CI 0.5–1.8), and 0.7/100,000 (95% CI 0.3–1.4).
TABLE 1: Incidence of paediatric inflammatory bowel disease and its subtypes in New Zealand in 2016
The incidence of IBD in children younger than 10 years in New Zealand in 2015 was 2.3/10,000 (95% CI 1.3–3.7), whereas the incidence in children aged 10 to 15 years was 10.4/100,000 (95% CI 7.4–14.2).
Sex Distribution of Paediatric Inflammatory Bowel Disease in New Zealand
Of the 51 people newly diagnosed with paediatric -onset IBD in 2015, 29 were boys leading to a 1.3:1 male to female ratio. The male to female ratio of the CD cohort was 1.4:1 (20 affected males). The ratios for UC and IBDU were 1.5:1 and 0.8:1, respectively. There was no significant difference between the sex for IBD, or any of the subtypes, among the cohort (P = 0.3).
Age at Diagnosis of Paediatric Inflammatory Bowel Disease in New Zealand
The median age at diagnosis of children in New Zealand diagnosed with IBD in 2015 was 12.4 years (IQR 9.7–14.3 years). By IBD subtype the median age at diagnosis for CD, UC, and IBDU was 13.8 years (IQR 11.4–14.7), 11.3 years (IQR 8.1–13.3), and 2.4 years (IQR 1.5–12.2), respectively. One-way analysis of variance testing revealed a significant difference between the ages at diagnosis for the 3 IBD subtypes (P < 0.0001).
Ethnic Distribution of Paediatric Inflammatory Bowel Disease in New Zealand
Of the 51 children diagnosed with IBD in 2015, 45 (88.2%) had at least 1 parent, or identified, as ethnically European. Four (7.8%) had at least 1 parent, or identified, as Asian, whereas 2 (3.9%) were of Middle Eastern heritage. The patients who identified as Asian were of Indian ethnicity, whereas the 2 of Middle Eastern heritage were of Arabic descent. One child had 1 African parent, whereas 2 (3.9%) identified as Maori. There were no children of Pacific Island ethnicity.
Family History of Inflammatory Bowel Disease
Thirteen (25.5%) of those diagnosed with IBD in NZ younger than 16 years in 2015 had a documented positive family history of IBD. Eight were first-degree relatives, 2 second-degree relatives, 2 greater than fourth-degree relatives, and the degree of relatedness was not specified in 1 instance.
Investigation Modalities Used at the Time of Diagnosis
All 51 patients newly diagnosed with paediatric IBD in New Zealand in 2015 had a colonoscopy as part of their diagnostic work-up. All but 4 (7.8%) of those patients had an upper gastrointestinal endoscopy at the same time. Only 2 patients were cared for exclusively by an adult gastroenterologist.
Of the incident cohort, 32 patients underwent a magnetic resonance enterography (MRE) within 6 months of diagnosis. In 2 cases, an MRE was not performed as the patients’ families declined the study. In 6 cases, the patient underwent a barium meal and follow-through and in 1 instance, the patient was unable to tolerate the oral barium required to perform the study. In 3 cases, a computed tomography abdomen was performed which provided enough detail on small bowel involvement so that MRE was not undertaken. In 3 out of the 4 cases of distal colitis (EI), a dedicated small bowel study was not requested, according to national guidelines; the fourth child underwent a computed tomography abdomen after not being able to tolerate an MRE. In 5 instances, dedicated small bowel study was not performed within 6 months of diagnosis for no clear reason, although 2 of those children had undergone magnetic resonance cholangiopancreatography for IBD-associated liver disease.
Paris Classification of Paediatric Inflammatory Bowel Disease in New Zealand
Cases with CD and UC were classified according to the Paris classification system for paediatric IBD (22) Table 2 ). Ileocolonic CD was the most common lower gastrointestinal tract location with 20 (58.8%) of the included patients affected. Twenty-six (76.5%) patients with CD had known upper gastrointestinal tract involvement, whereas in 2 (5.9%) cases upper gastrointestinal endoscopy was not performed at diagnosis. Among the CD cohort, 5 (14.7%) had perianal involvement. With regards to disease phenotype, 32 (94.1%) had inflammatory CD, whereas 2 (5.9%) had penetrating CD at diagnosis.
TABLE 2: Paris classification Crohn disease cohort in New Zealand , 2015
Of the 10 new cases of paediatric UC diagnosed in 2015 in New Zealand , 4 had proctitis (E1), 2 had left-sided colitis (E2), and 4 had pancolonic involvement (E4). There were no cases of atypical UC, that is, with upper gastrointestinal tract involvement, relative rectal sparing or periappendiceal inflammation in the absence of pancolitis.
Surgery for Paediatric Inflammatory Bowel Disease in New Zealand
One child diagnosed with perianal CD in 2015 required a fistulotomy. That was the only surgery for any of the newly diagnosed with paediatric IBD cases in New Zealand in 2015.
Extraintestinal Manifestations of Paediatric Inflammatory Bowel Disease in New Zealand
Of the 51 patients newly diagnosed with paediatric IBD in New Zealand in 2015, 8 (15.7%) were found to have extraintestinal manifestations of their disease either on self-reporting or physical examination, at the time of diagnosis. (Table 3 ). Of the patients who had orofacial manifestations of IBD, 2 had orofacial granulomatosis whereas 1 had oral ulcers (and erythema nodosum).
TABLE 3: Extraintestinal manifestations of newly diagnosed paediatric inflammatory bowel disease cases in New Zealand for 2015
DISCUSSION
The incidence rates for paediatric IBD, CD, and UC in New Zealand in 2015 were 5.2, 3.5, and 1.0 per 100,000 children , respectively. These figures are considerably higher than those obtained from the national survey conducted just over a decade earlier—2.9, 1.9, and 0.5/100,000 children for IBD, CD and UC, respectively. (17)
The study by Yap et al (17) New Zealand Paediatric Surveillance Unit. The disadvantages of a survey notwithstanding, it is worth noting that the study, conducted between 2002 and 2003, reported an admirably high response rate of 95% and 97%, respectively from paediatricians and “other specialists working predominantly with children ” over the 2-year study period.
Although the earlier national study and the present one have substantial methodological difference, there is good reason to accept their respective results’ as being rigorous. Taken together, they show a near doubling of the incidence of paediatric IBD and its subtypes within a 12-year period. The nationwide incidence rate obtained in 2015 by the PINZ study is comparable with those reported in Europe (11,14,25) (26) (5) (27) incidence rates. The single-year incidence rate obtained is likely to be reflective of national trends based on the point prevalence of IBD in New Zealand in 2015 (28) incidence of paediatric IBD in the Canterbury region (29)
The ratio of CD:UC:IBDU among the incident cohort was approximately 5:1.4:1. This suggests a significant predominance of CD in New Zealand . The Quebec (30,31) (5,9,32–34) paediatric IBD trends (2,9,32,33,35)
International (21) (36) paediatric IBD include upper and lower gastrointestinal tract endoscopy. Indeed, except in cases of distal colitis, small bowel imaging is required to make a complete and accurate diagnosis (36) paediatric IBD in New Zealand in 2015 underwent colonoscopy. Among them, 4 (7.8%) did not undergo an upper gastrointestinal tract endoscopy at the time of diagnosis. Among patients who should have had dedicated small bowel imaging based on the aforementioned guidelines, 5 did not. Of that number, however, 2 underwent magnetic resonance cholangiopancreatography for IBD-related liver disease and a third child was aged <5 years, which would have likely made small bowel imaging practically difficult.
New Zealanders of European ethnicity were over-represented among all children diagnosed with IBD in the country in 2015. The methodology employed by the PINZ study of recording multiple ethnicities for patients who identify with >1 is also the same as is employed by Statistics New Zealand —a strength of the present study. The reasons for the ethnic variation among incidence rates of paediatric IBD in New Zealand remain unclear.
By virtue of engaging every paediatric gastroenterologist currently practising in New Zealand , the PINZ study was able to ensure full co-operation of the 2 centres in New Zealand that provide specialist paediatric gastroenterological care. This ensured a thorough and robust search for every patient with IBD meeting criteria to be included in the present study. Further to that, in centres in which older children were sometimes cared for in adult services (either in the public or private sectors) key adult gastroenterologists were contacted, and co-operated in every instance. The study methodology employed consisted of robust case note review by a single investigator (R.N.L.) who also classified IBD phenotype—a method used elsewhere (5)
It is conceivable that, particularly in the smaller centres in New Zealand , some cases of paediatric IBD may be managed locally with no specialist (paediatric ) gastroenterology input. The design of the PINZ study means that cases such as those will not have been identified. Consensus among senior gastroenterologists in New Zealand , however, is that that number is likely to be small. Taking into account that possible oversight, the incidence rates here given might in fact be an underestimation.
Epidemiological studies provide information which helps to guide health service provision within a country. In instances in which disease incidence is thought to be increasing, point prevalence and prospectively collected incidence rates are particularly crucial and the PINZ study hopes to answer both these questions with respect to New Zealand .
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