The household interview was completed by 4,773 (71.0%) of the 6,719 adults aged 20 years and older who were selected to participate in the NHANES 2005-06. Of these, 465 (9.7%) did not complete the MEC health examination components which included the Bowel Health questionnaire; however, no subjects declined to complete only the questions on FI. The 2,079 males and 2,229 females who completed the Bowel Health questionnaire provided the data for this study. The demographics of the sample are described in . All age groups were well represented. Hispanics constituted 23.0% and non-Hispanic blacks were 22.1% of the sample.
Characteristics of the sample‡
An estimated 8.3% (CI 7.1, 9.5) of non-institutionalized adults in the United States report FI at least once during the last 30 days; this estimate corresponds to 18 million people as of April 1 to July 1, 2006. FI was found to be equally common in women (8.9%; CI 7.2, 10.5) and men (7.7%; CI 6.0, 9.4; p=0.31).
Liquid stool incontinence was the most common type of FI as shown in and was reported equally often by women and men (p=0.69). Solid stool incontinence was more likely to be reported by women than by men (p=0.038). Incontinence of more than one consistency was reported by 26.1% (CI 21.1, 31.0) of participants with FI.
Composition and frequency of leakage: Percent of women and men with each type of fecal incontinence
Most participants with FI reported that it occurred one to three times per month (). However, 2.8% (CI 1.9, 3.7) of women and 2.6% (CI 1.7, 3.4) of men had FI at least once a week. A frequency of one or more FI episodes per day was reported by 0.9% (CI 0.6, 1.2) or 90 people out of a thousand.
The NHANES provided an opportunity to assess how prevalence estimates would be affected by including accidental loss of gas in the definition, which would correspond to the definition of anal incontinence16
. Leakage of gas at least once in the last month was reported by 51.0% (CI: 45.7, 56.3) of women and 46.2% (CI: 42.4, 49.9) of men, and daily leakage of gas was reported by 20.5% (CI: 17.6, 23.4) of women and 24.0% (CI: 20.7, 27.3) of men.
As shown in , there was a linear progression in the prevalence of FI with age for both women and men (p<0.01 for both). For women and men combined, prevalence increased from 2.6% (CI 1.5, 3.8) at 20-29 years of age up to 15.3% (CI 11.5, 19.0) in participants aged 70 and over. However, FI was not significantly associated with race/ethnicity, marital status, education, or family income for women or men after adjusting for age (data not shown).
Prevalence of fecal incontinence by age group in females and males. Bars represent 95% confidence intervals.
lists candidate risk factors that were significantly associated with FI in either women or men when tested individually; associations are expressed as age-adjusted odds ratios and 95% confidence intervals. This table also shows the final multivariate models for women and men. Supplemental tables S1 and S2
(see journal website) provide estimates of the prevalence of FI by all risk factors considered in this study.
Odds Ratios for Variables Associated with Fecal Incontinence*
Participants who reported that their bowel movements were usually mushy or watery were substantially more likely to report FI compared to participants with normal stool consistency () even after multivariate adjustment for other risk factors. For women, the findings for stool frequency paralleled those for stool consistency: having more than 21 bowel movements per week was significant in the final model. However, after multivariate adjustment this relationship did not hold for men.
Figure 2 Prevalence of fecal incontinence by usual stool consistency in females and males. Bars represent 95% confidence intervals. For both women and men, the odds of FI was significantly increased (p<0.001) for subjects whose usual stool consistency (more ...)
The inability to engage in physical activity was significantly associated with FI in women but not men (). In the bivariate analyses, engaging in vigorous physical activity appeared to be protective in women, but this association did not survive multivariate adjustment. Similarly, in bivariate analyses obesity (BMI ≥30) was associated with a higher prevalence of FI compared to normal or low weight (BMI <25) in women, but this association was no longer significant after multivariate adjustment.
Women with chronic illnesses were at increased risk of FI, but this association was not significant for men. However, in men (but not women) self-reported poor health was significantly associated with FI.
In women, the prevalence of FI increased with increasing numbers of vaginal deliveries from 5.9% (CI 3.2, 8.6) in women with no vaginal deliveries to 15.1% (CI 11.9, 18.3) in women with 4 or more vaginal deliveries (p<0.0001; Supplemental Table S2
). However, number of vaginal deliveries was no longer significantly associated with FI after adjustment for age (p=0.09) and other risk factors (p=0.57).
FI was significantly associated with UI in men; for women, the bivariate association between UI and FI was significant, but after multivariate adjustment, this association was no longer significant in women (p=0.054; see ). Both UI and FI were reported by 2.7% (CI 1.9, 3.6) of women and 1.1% (CI 0.7, 1.5) of men in the non-institutionalized population. The overall prevalence of UI and FI occurring together (women and men combined) was 1.9% (CI 1.5, 2.4).