Our nationwide analysis has demonstrated geographic variations in the burden of diverticulitis and underscores rapidly increasing rates of diverticulitis-associated hospitalizations among individuals younger than age 45 years. These findings have implications for understanding the underlying etiology of diverticulitis as well as for the timely diagnosis of this condition in younger individuals. The rising epidemiological trends and geographic variations in diverticulitis-associated admissions, particularly among younger individuals, may correlate with observed temporal changes and regional differences in diet and obesity in America.
Diverticular disease is an age-related disorder of the large bowel affecting greater than half of the population over the age of 65 years[13
]. Current evidence suggests that dietary deficiency (of fibre), colonic pressure, motility changes and colonic structural alterations may collectively contribute to diverticula formation[4
]. Parallel epidemiological trends of decreasing dietary fibre and increasing diverticular disease have led to a hypothesized role of fibre deficiency in the pathogenesis of diverticular disease[6,14
]. A large prospective study of 43 888 US male health care professionals[15
] found that a decreased intake of insoluble dietary fibre, specifically fruits and vegetables, was associated with increased symptomatic diverticular disease. Similarly, obesity has also been linked to higher incidence of diverticulitis and diverticular bleeding[7,8
]. It is hypothesized that adipose tissue secretes numerous cytokines that are known to participate in local and generalized inflammation and may play a role in the development of diverticulitis[16
Our study showed that the overall rates of acute diverticulitis hospitalizations increased in the US in the last decade, which has been previously reported in the US[9
] as well as in the UK[17
] and Finland[18
]. An epidemiological study of adults aged 40-74 years has also shown a rise in obesity, decreased physical activity, and decreased fibre intake which may all contribute to the increasing incidence of diverticular disease[19
]. Similarly, a decline in fibre intake among children and 3-fold rise in childhood obesity in the US over the last 3 decades may also partially explain the sharp rise in admissions for diverticulitis among younger age groups[20,21
The higher prevalence of obesity in the South and Midwest may correlate with our findings of higher rates of diverticulitis admissions in those regions compared to the West. Data from the Center for Disease Control showed that in 1991, the Midwest and the South had higher obesity rates compared to the Northeast and West, and this difference had persisted in the ensuing decade 2000[22
]. Data from NHANES-III also showed that BMI was greater in the South and Midwest compared to the other regions[23
]. Childhood obesity has been similarly shown to be most prevalent in the South ( ≥ 18%) while being least prevalent in the West (11.4%)[20
Regional variation in diet may also contribute to geographic differences in diverticulitis admissions. Based on self-reported data, residents from the South consumed more fatty acids and the least amount of fibre, while those from the West consumed higher amounts of fibre than other regions[23
]. One could hypothesize that there may be a protective association between higher fibre intake in the West and corresponding relatively lower age-adjusted rates of diverticulitis admissions. However, the roles of dietary fibre and obesity in geographic variations in diverticulitis remain speculative, and do not explain high rates of diverticulitis admissions in the Northeast. Thus, other environmental and health systems-based factors may be involved. Racial and ethnic differences in risk of diverticulitis may also contribute to geographic variations in hospital admissions for diverticulitis, particularly in the West, where there is a higher composition of Hispanics and Asians. There is evidence that these ethnic groups may be at lower risk for diverticulitis[24,25
]. Unfortunately, because nearly 25% of racial and ethnic data is missing in the NIS database, we were not able to readily determine race- and ethnic-specific rates in diverticulitis admissions.
Our current study has several limitations inherent to administrative data analyses. The NIS data set does not contain personal identifiers, which does not allow linkage to medical records in order to validate ICD-9 codes for diverticulitis. However, we would not expect the degree of errors in administrative coding to be different with respect to time or age. Thus, this type of non-differential misclassification usually leads to conservative estimates of temporal trends. Additionally, this study evaluated only rates of hospitalization, and would not have included milder cases of diverticulitis managed in an outpatient setting. Furthermore, this is a cross-sectional study and we are unable to longitudinally follow patients after discharge to assess long-term mortality and morbidity such as recurrent diverticulitis or surgery.
Despite these limitations, this nationally representative analysis has demonstrated geographic variations in epidemiological trends in the burden of diverticulitis that will hopefully stimulate hypotheses into the aetiology of diverticular disease. Prospective studies are needed to determine if there is an association between diverticulitis and obesity, dietary intake, and other environmental factors, particularly among younger adults. From a clinical perspective, these findings drive the need for increased vigilance for diverticular disease among younger adults presenting with abdominal pain.