In a population-based study, we found infection within the first year of life to be associated with a diagnosis of IBD. This might be due to use of antibiotics or a physiologic defect at a critical age for gut microbiome development.

Data on 825 IBD cases and 5999 matched controls were available from 1979. Maternal diagnosis of IBD was the greatest risk factor for IBD in offspring (odds ratio [OR], 4.53; 95% confidence interval [CI], 3.08–6.67). When we assessed neonatal events, only being in the highest vs lowest socioeconomic quintile increased risk for later development of IBD (OR, 1.35; 95% CI, 1.01–1.79). For events within the first year of life, being in the highest socioeconomic quintile at birth and infections (OR, 1.39; 95% CI, 1.09–1.79) increased risk for developing IBD at any age. Infection in the first year of life was associated with diagnosis of IBD before age 10 years (OR, 3.06; 95% CI, 1.07–8.78) and before age 20 years (OR, 1.63; 95% CI, 1.18–2.24). Risk for IBD was not affected by gastrointestinal infections, gastrointestinal disease, or abdominal pain in the first year of life.

We collected data from the University of Manitoba IBD Epidemiology Database, which contains records on all Manitobans diagnosed with IBD from 1984 through 2010 and matched controls. From 1970 individuals’ records can be linked with those of their mothers, so we were able to identify siblings. All health care visits or hospitalizations during the neonatal and postnatal periods were available from 1970 through 2010. We collected data on infections, gastrointestinal illnesses, failure to thrive, and hospital readmission in the first year of life and sociodemographic factors at birth. From 1979, data were available on gestational age, Apgar score, neonatal admission to the intensive care unit, and birth weight. We compared incident rate of infections, gastrointestinal illnesses, and failure to thrive between IBD cases and matched controls as well as between IBD cases and siblings.

Health providers and parents need to be more circumspect about antibiotic use especially for young children. Further research should be undertaken to study breastfeeding and diet in the first year of life to determine their impact on IBD risk

This was an administrative database study and it was not clear whether the risk posed by infections were from infections per se or the antibiotics used to treat them, among other variables.

The first year of life is a critical time for development of the gut microbiome and it is unknown whether neonatal or postnatal events (for up to one year and longer) could impact the risk for developing IBD.

It is unknown what triggers the development of inflammatory bowel disease (IBD). However, there is emerging evidence of important dysbiotic changes in the gut microbiome in persons with IBD, such as reduced diversity and alterations in certain species.A variety of factors can change the gut microbiome, such as antibiotic ingestion or dietary changes. However, the permanence of the gut microbiome changes may be dependent on the timing and/or duration of what factor is introduced. The gut microbiome undergoes the most change from birth until 1–2 years of age, when the microbiota composition stabilizes.Hence, events that promote alterations in the composition of the gut microbiome in the first year of life may have important effects on its more permanent composition. This, in turn, may impact on the ultimate development of IBD. Infections that impact on the gut microbiome and antibiotic use in the first year of life through their effects on the gut microbiome may, therefore, impact on the ultimate development of IBD.

Therefore, we aimed to determine whether there was an increased risk of IBD among persons who had critical events at birth or within the first year of life, which would be expected to lead to alterations in the gut microbiome. Further, we explored whether these events affected risk for IBD differentially at different ages of IBD onset.

We compared incident rate of infections, gastrointestinal illnesses, and failure to thrive identified from outpatient visits and on hospitalizations (from the hospital discharge abstracts) between IBD cases and their matched controls, as well as between IBD cases and their siblings. We also analyzed neonatal events. For all of the neonatal events as well as events within the first year of life, we assessed for subsequent development of IBD at any age, development of IBD before age 10 years and development of IBD before age 20 years. We assessed for all diagnoses of IBD and then separately for diagnoses of Crohn’s disease and for ulcerative colitis. Comparisons used Fisher’s exact test for each category of clinical disease assessed, for socioeconomic status at birth, for rural vs urban residence at birth and for neonatal parameters (mode of delivery, gestational age, birth weight, Apgar score, and neonatal intensive care unit admission). Conditional logistic regression models estimated the odds of developing IBD compared to either matched controls or siblings, and odds ratios (ORs) with 95% confidence intervals (CI) are reported for all individuals available from 1979 so that all variables could be included. We conducted a separate conditional logistic regression model for all individuals available since 1970, excluding the neonatal events available only since 1979 in the model. We repeated these analyses comparing IBD cases with their unaffected siblings.

The University of Manitoba IBD Epidemiology Database contains records on all Manitobans diagnosed with IBD between 1984 and 2010. Each individual is identified by a unique personal health identification through which all health system contacts can be tracked dating back to 1984. In 1995, we validated an administrative definition of IBD based on frequency of health system contacts.We identified all persons with IBD and created a matched cohort of controls, matching 10 controls without IBD by age, sex, and area of residence to each IBD case. Our administrative definition of IBD allowed updating our database with new cases on an ongoing basis. Starting in 1970, 6-digit family health registration numbers, shared by a mother and all of her offspring, have been used in Manitoba and allow for the accurate linkage of the health care utilization profiles of mothers with their children.Information on diagnoses associated with health care visits or hospitalizations during the neonatal and postnatal periods was available from 1970 to 2010. All hospitalizations and discharge diagnoses (up to 20 by International Classification of Disease, 9Revision, Clinical Modification codes to 2004 and up to 25 by International Classification of Disease, 10Revision, Clinical Modification codes after 2004) and outpatient contacts (by International Classification of Disease, 9Revision, Clinical Modification codes) were tracked. The Medical Records Department of the Children’s Hospital of Winnipeg provided all International Classification of Disease, 10Revision codes identified as the number one discharge abstract diagnosis for the hospitalizations of all children under age 3 years in the years 2013–2016. This allowed the casting of a wide net for possible infections or gastrointestinal illnesses associated with early life hospitalization. We assessed for 26 different categories of infection, 4 categories of gastrointestinal illness, failure to thrive, and for hospital readmission. The types of infections and gastrointestinal illnesses are listed in Supplementary Table 1 . The infections included those likely to require antibiotic therapy and also viral infections; it was considered that, if a child was sufficiently ill to be admitted to hospital, even if the discharge diagnosis was that of a viral infection, at some point the child may have received antibiotic therapy. However, we also included a separate analysis excluding what were diagnosed as viral infections. We assessed for the occurrence of those events within the first year of life. We also assessed for those events within the first 3 years of life. Inpatient and outpatient diagnoses were combined in each category to increase the power to determine if any diagnoses with these conditions were associated with a later diagnosis of IBD. We assessed for maternal diagnosis of IBD and we assessed for mode of delivery (cesarean section vs vaginal delivery). Considering that some diagnoses of IBD could actually be cases of immunodeficiency syndromes and that persons who are immunodeficient would incur more infections and antibiotic use, we compared the rates for immunodeficiency syndromes among persons with IBD and controls by International Classification of Disease, 9Revision, Clinical Modification code 279 and by the following International Classification of Disease, 10Revision, Canada codes including immunodeficiency with predominantly antibody defects (D80), combined immunodeficiencies (D81), immunodeficiency associated with other major defects (D82), common variable immunodeficiency (D83) and other immunodeficiencies (D84). From 1979 onward, data were available on gestational age, Apgar score, neonatal intensive care unit admission, and birth weight. We also assessed rural vs urban residence and family socioeconomic status by quintile at birth. To assess socioeconomic status, we used the median household income quintile for the area of residence at the time of birth identified by the subjects’ 6-digit postal code at the time of birth.

Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, Among All Persons With Inflammatory Bowel Disease (n = 827) Compared to Sibling Controls (n = 994)

Table 6 Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, Among All Persons With Inflammatory Bowel Disease (n = 827) Compared to Sibling Controls (n = 994)

In assessing for immunodeficiency disorders at any time in life, we found them to be diagnosed in 34 of 825 (4.1%) of IBD cases and in 220 of 5999 (3.67%) controls (P = .49). Hence, neither overall childhood antibiotic use nor immunodeficiency disorder was associated with a diagnosis of IBD.

Because infections in the first year of life was a strong predictor of developing IBD in several of our analyses, we explored the direct use of antibiotics where we could, and the diagnoses of immunodeficiency syndromes. From 1996 through 2010 (the years in which antibiotic data were available in our administrative data) within our cohort, there were only 33 individuals with IBD and 270 controls who were born after 1996. For this group of 303 individuals, the mean number of antibiotic prescriptions in the first 10 years of life was 8.97 (95% CI, 6.44–11.50) among persons with IBD compared with a mean of 7.59 (95% CI, 6.63–8.55) among controls (P = .34 for the difference between IBD cases and controls). We modeled antibiotic users, defined by actual antibiotic prescriptions in the first year of life; socioeconomic status at birth; and rural vs urban residence at birth, and there was a trend for antibiotic prescription in the first year of life predicting later IBD diagnosis; however, it was not statistically significant (OR, 1.66; 95% CI, 0.74–3.74; P = .21).

We undertook an analysis assessing only hospitalizations for infections (excluding outpatient contacts for infection). This did not prove to be significantly predictive of developing IBD, although the sample size was likely too small. We also undertook an analysis of predictors of developing IBD excluding viral infections in the first year of life and in this model infections in the first year of life did not prove to be predictive of developing IBD. Only maternal diagnosis of IBD retained its significance as a predictor ( Supplementary Table 6 ). Finally, we undertook an analysis of predictors of IBD, including infections in the first 3 years of life and we found that infections did not predict development of IBD. In this model only maternal diagnosis of IBD and being in the highest or second highest socioeconomic quintile compared to the lowest at birth predicted development of IBD ( Supplementary Table 7 ).

In a model including data dating back to 1970 from all 1671 persons with IBD and 10,488 controls for mothers IBD status, socioeconomic status at birth, urban vs rural residence, and cesarean section were assessed. For persons with IBD diagnosed at any age, having a maternal IBD diagnosis (OR, 4.54; 95% CI, 3.40–6.06; P < 0.001) and being born into the highest socioeconomic quintile vs the lowest (OR, 1.29; 95% CI, 1.05–1.59; P = 0.01) were predictive of developing IBD. Being born in rural area was protective against developing IBD (OR, 0.84; 95% CI, 0.72–0.99; P = 0.04).

The predictors of being diagnosed with IBD under age 10 (n = 97 IBD cases and 748 controls) included maternal diagnosis of IBD (OR, 5.92; 95% CI, 1.76–19.98), having an infection in the first year of life (OR, 3.06; 95% CI, 1.07–8.78), and being born rural vs urban (OR, 2.54; 95% CI, 1.24–5.20) ( Table 4 ). The predictors of being diagnosed with IBD under age 20 years (n = 499 IBD cases and 4503 controls) included maternal diagnosis of IBD (OR, 4.95; 95% CI, 3.18–7.71), having an infection in the first year of life (OR, 1.63; 95% CI, 1.18–2.24), and being in the highest socioeconomic quintile compared with the lowest at birth (OR, 1.43; 95% CI, 1.02–2.00) ( Table 5 ). Maternal diagnosis of IBD was a significant predictor of developing Crohn’s disease before age 10 years, but no variables significantly predicted development of ulcerative colitis before age 10 years ( Supplementary Tables 2 and 3 ). Maternal diagnosis of IBD was a significant predictor of developing either Crohn’s disease or ulcerative colitis before age 20 years and infection in the first year of life was a significant predictor of developing Crohn’s disease but not ulcerative colitis before age 20 years ( Supplementary Tables 4 and 5 ).

Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, Under Age 20 Years Among All Persons With Inflammatory Bowel Disease (n = 591) Compared to Controls (n = 4491)

Table 5 Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, Under Age 20 Years Among All Persons With Inflammatory Bowel Disease (n = 591) Compared to Controls (n = 4491)

Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, Under Age 10 Years Among All Persons With Inflammatory Bowel Disease (n = 97) Compared to Controls (n = 748)

Table 4 Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, Under Age 10 Years Among All Persons With Inflammatory Bowel Disease (n = 97) Compared to Controls (n = 748)

We were able to link the administrative health records of 1671 IBD cases, 1740 siblings, and 10,488 matched controls to their mothers dating back to 1970. The median age of the IBD cohort was 20.0 years (range, 1.0–39.0 years; 25percentile, 16; 75percentile, 25). A total of 6824 individuals (n = 825 for IBD cases and n = 5999 for controls) were available to examine all events dating back to 1979. The median age for this cohort was 17.0 years (range 1–30.0; 25percentile, 13; 75percentile, 21). This cohort including data dating back to 1979 was used for the following analyses. Among IBD cases, 97 were diagnosed before age 10 years, 499 were diagnosed between ages 10–20 years, and 229 were diagnosed after age 20 years. The strongest predictor for development of IBD in all models was maternal history of IBD (OR, 4.53; 95% CI, 3.08–6.67 in the model including all neonatal and first year of life events). The model assessing all neonatal events and events in the first year of life found that being in the highest or the second highest socioeconomic quintile at birth vs the lowest (OR, 1.35; 95% CI, 1.01–1.79 and OR, 1.37; 95% CI, 1.06–1.77, respectively) and infections within the first year of life were associated with later development of IBD at any age (OR, 1.39; 95% CI, 1.09–1.79) ( Table 1 ). When assessing Crohn’s disease (n = 482) separately from ulcerative colitis (n = 343), maternal history of IBD was strongly predictive for both diseases, and having an infection in the first year life trended toward being predictive but did not reach statistical significance in either disease ( Tables 2 and 3 ). Being in a higher socioeconomic status at birth compared to the lowest quintile was predictive of developing ulcerative colitis for all 4 socioeconomic quintiles above the lowest. Assessing neonatal events only, for later development of IBD, the only predictors of later development of IBD were being in the highest vs lowest socioeconomic status by quintile (OR, 1.35; 95% CI, 1.01–1.79) or being in the second highest versus lowest socioeconomic quintile (OR, 1.37; 95% CI, 1.06-1.77).

Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Ulcerative Colitis, at Any Age Among All Persons With Ulcerative Colitis Compared to Controls

Table 3 Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Ulcerative Colitis, at Any Age Among All Persons With Ulcerative Colitis Compared to Controls

Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Crohn’s Disease, at Any Age Among All Persons With Crohn’s Disease Compared to Controls

Table 2 Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Crohn’s Disease, at Any Age Among All Persons With Crohn’s Disease Compared to Controls

Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, at Any Age Among All Persons With Inflammatory Bowel Disease Compared to Controls

Table 1 Association Between Demographic Variables at Birth and Clinical Events in the First Year of Life (Infections, Gastrointestinal Illnesses, Failure to Thrive, and Hospital Readmission) and the Development of Inflammatory Bowel Disease, at Any Age Among All Persons With Inflammatory Bowel Disease Compared to Controls

Discussion

8 Stiemsma L.T.

Reynolds L.A.

Turvey S.E.

Finlay B.B. The hygiene hypothesis: current perspectives and future therapies. 9 Alter M.

Zhen-xin Z.

Davanipour Z.

et al. Does delay in acquiring childhood infection increase risk of multiple sclerosis?. , 10 Gent A.E.

Hellier M.D.

Grace R.H.

et al. Inflammatory bowel disease and domestic hygiene in infancy. , 11 Forste R.

Hoffmann J.P. Are US mothers meeting the Healthy People 2010 breastfeeding targets for initiation, duration, and exclusivity? The 2003 and 2004 National Immunization Surveys. 12 Palmer C.

Bik E.M.

DiGiulio D.B.

et al. Development of the human infant intestinal microbiota. 12 Palmer C.

Bik E.M.

DiGiulio D.B.

et al. Development of the human infant intestinal microbiota. 13 Bernstein C.N.

Banerjee A.

Targownik L.E.

et al. Cesarean section delivery is not a risk factor for development of inflammatory bowel disease: a population-based Analysis. 14 Benchimol E.I.

Kaplan G.G.

Otley A.R.

Nguyen G.C.

Underwood F.E.

Guttmann A.

et al. Rural and urban residence during early life is associated with risk of inflammatory bowel disease: a population-based inception and birth cohort study. We found that the strongest and most consistent predictor of developing IBD was having a mother with a diagnosis of IBD. This might reflect either an important genetic effect or an important environmental effect or a combination of both. Children share a close environment with their mothers, especially in their developing years, and it has been shown that the gut microbiome of children increasingly mirrors that of their parents’ gut microbiome from the second through the sixth month of life.We also found that persons with IBD were significantly more likely to be born into higher socioeconomic status families. The association between higher socioeconomic status and IBD may be reflective of the hygiene hypothesis, which posits that a cleaner lifestyle is associated with an increase in chronic immune diseases.This lifestyle may involve less risk for childhood infections, cleaner water sources and toilet facilities, and less home crowding. It also may reflect greater attention to health care. Being born into a higher socioeconomic lifestyle may impact on duration of breastfeeding and timing and types of foods that are introduced in the first year of life.Because higher socioeconomic status at birth poses a risk for developing IBD, and prolonged breastfeeding may be protective against developing IBD, then further research will need to tease out which has a greater impact on ultimate development of IBD.We have previously shown that among persons ultimately diagnosed with IBD, compared to controls there was no difference in likelihood of initiating breastfeeding just after delivery,however, studies are needed to ascertain whether the duration of breastfeeding, as well as the exclusivity of breastfeeding (to what extent or at what age formula or table food was introduced) impact on the development of IBD. This will require a prospective study. Being born in rural vs urban settings was predictive of developing IBD (more specifically Crohn’s disease) among children under age 10 years, but not for IBD diagnoses at other ages. This contrasts with a Canada-wide report that suggested that rural residence was protective against developing IBD mostly among children who lived rurally under age 5 years, but found a wide variation among provinces.When we assessed a larger sample size excluding neonatal events and assessing maternal and demographic factors with data going back to 1970 (n = 1670 for persons with IBD), being born rural was protective against developing IBD. Further research is required to determine what aspects of a higher family socioeconomic status at birth and family life in general contribute to an increased risk of chronic immune diseases, especially IBD.

15 Shaw S.

Blanchard J.F.

Bernstein C.N. Association between the use of antibiotics in the first year of life and pediatric inflammatory bowel disease. , 16 Ungaro R.

Bernstein C.N.

Gearry R.

et al. Antibiotics associated with increased risk of new-onset Crohn's disease but not ulcerative colitis: a meta-analysis. 15 Shaw S.

Blanchard J.F.

Bernstein C.N. Association between the use of antibiotics in the first year of life and pediatric inflammatory bowel disease. 17 Kelsen J.R.

Sullivan K.E. Inflammatory bowel disease in primary mmunodeficiencies. Finally, infections in the first year of life were predictive of development of IBD at any age and with the strongest association for infections in the first year of life and development of IBD before age 10 years. We, and others, have previously shown that antibiotics early in life,especially in the first year of life,can increase the risk of IBD development in childhood. We did not find that infections in the first 3 years of life were predictive of developing IBD, nor did we find that antibiotic usage in the first 10 years of life were predictive of an IBD diagnosis, although this latter analysis had a very limited sample size. It is unclear if the risk posed by infections in the first year of life is a manifestation of the infection itself per se or the use of antibiotics to treat the infections. We do not believe the risk posed by infections in the first year of life was secondary to persons with IBD being more likely to have an immunodeficiency disorder; disorders that can often present with an IBD-like picture.We did not find more immunodeficiency disorders diagnosed in our IBD cohort compared with controls. Hence, the first year of life is potentially a critical time for risk for IBD development.

18 Kalliomaki M.

Salminen S.

Arvilommi H.

et al. Probiotics in primary prevention of atopic disease: a randomized placebo-controlled trial. How can these data be used in a practical sense to potentially impact on later IBD diagnosis? Limiting antibiotic usage in the management of routine infections could be desirable; however, it would be difficult to curb antibiotic use for many of the infections as serious as the ones we assessed. If it is increasingly accepted that antibiotics in the first year of life truly pose a risk for later chronic immune disease like IBD, then research is warranted to determine exactly what antibiotic intake does to infant gut microflora or intestinal or systemic immune responses. Interventions such as probiotic or prebiotic use could be considered after a course of antibiotics in children to prevent development of IBD or other chronic immune diseases.

It was particularly noteworthy that there were no differences among possible predictive factors for persons with IBD compared to their unaffected sibling controls. Those ultimately developing IBD compared to their unaffected siblings had similar neonatal events and similar events within the first of life in relation to infections and need for hospitalizations. As infection in the first year of life (and possibly the use of antibiotics to treat infection) is an important risk factor in our comparison of IBD cases with controls, it is uncertain why incidence of infection was not different for cases in comparison with sibling controls. Perhaps this suggests that because cases and siblings share genetics and environment, something unique must be occurring to cases that has not occurred to their unaffected siblings. Perhaps the genes not shared by the unaffected sibling include protective genes, which suggest a closer genetic evaluation of the differences between affected persons and their unaffected siblings may be fruitful. Secondly, while siblings share an environment and likely a similar diet while growing up, our findings suggest that there must be some environmental differences that we have not captured with our analyses. This may warrant a careful scrutiny of the diet and environment of unaffected siblings at the time of index case diagnosis. Some of those unaffected siblings may become affected over time, but many will not. The timing of the assessment of the unaffected siblings’ environment and personal health attributes is critical.

13 Bernstein C.N.

Banerjee A.

Targownik L.E.

et al. Cesarean section delivery is not a risk factor for development of inflammatory bowel disease: a population-based Analysis. 19 Bernstein C.N.

Burchill C.

Targownik L.E.

et al. Maternal infections that would warrant antibiotic use antepartum or peripartum are not a risk factor for the development of IBD: a population based analysis. 20 Neu J. Preterm infant nutrition, gut bacteria and necrotizing enterocolitis. , 21 Ubeda C.

Pamer E.G. Antibiotics, microbiota, and immune defense. No neonatal markers of health were found to be predictive of the eventual development of IBD. We have previously reported that neither undergoing birth by cesarean sectionnor being born to a mother who experienced antenatal or perinatal infections requiring antibiotics predicted later development of IBD.If delivery mode or maternal microbiota do influence the neonate’s microbiota at a vulnerable time, or if other markers of neonatal ill health, as we explored in this study, have an impact on neonatal microbiome or immune system development,these changes seemingly can all be overcome. However, experiencing an infection in the first year of life was predictive of developing IBD, particularly under age 20 years.

Gastrointestinal illnesses in the first year of life, including abdominal pain, were not found to be associated with later development of IBD. This should be reassuring for parents who worry about whether their young children with infectious or noninfectious gastrointestinal illnesses would be at risk at developing IBD. We did not have enough instances of failure to thrive to fully assess whether it associated with the development of IBD.

Our study has a number of limitations. While we examined the most serious infections experienced by children in our hospital setting, we could not assess definitively which of the conditions were associated with antibiotic prescriptions. It is speculative whether the association of infections in the first year of life with ultimate diagnosis of IBD at all ages is actually related to antibiotic use. It is possible that there are other factors that are as or more important in the first year of life that may increase the risk for IBD, such as diet, or duration of or exclusivity of breastfeeding in the first year of life. Further, other environmental factors in the home, such as smoking, may contribute to the risk for IBD. It is also possible that for onset of IBD into late teenage years and adulthood, there are other factors that overwhelm any risk posed by early life events. However, we did find the strongest association between infection in the first year of life and childhood-onset IBD. In fact, our data support the likelihood that triggers for IBD arising in children may very well be different from triggers that ultimately lead to adult-onset IBD. Risk factors posed from the diet or an environmental factor, such as smoking, may occur well after the first year of life. Because not everyone exposed to infections (or antibiotics) in their first year of life develop IBD, it is also possible that variables such as protective dietary factors experienced later in childhood may protect against the potential risk posed by harmful infections or the antibiotics used to treat them.

However, key strengths of our study include that it is population-based, that we have assessed for all possible diagnoses associated with significant infectious and gastrointestinal illness that lead to early childhood hospitalizations, and that we have included sibling controls. No increased risk was posed by infections in the first year of life in cases of IBD compared to their siblings, yet the risk existed compared to controls. This suggests that other non-communal environmental factors may also be of importance in the pathogenesis of IBD. More research on exploring the childhood household environment in persons who develop IBD compared to those who do not is warranted.