Incidence of post-infectious irritable bowel sydrome and functional intestinal disorders following a water-borne viral gastroenteritis outbreak

OBJECTIVES: Post-infectious irritable bowel syndrome (PI-IBS) may develop in 4 – 31 % of affected patients following
bacterial gastroenteritis (GE), but limited information is available on long-term outcome of
viral GE. During summer 2009, a massive outbreak of viral GE associated with contamination of
municipal drinking water (Norovirus) occurred in San Felice del Benaco (Lake Garda, Italy).
To investigate the natural history of a community outbreak of viral GE, and to assess the incidence
of PI-IBS and functional gastrointestinal disorders, we carried out a prospective population-based
cohort study with a control group.
METHODS: Baseline questionnaires were administered to the resident community within 1 month of the
outbreak. Follow-up questionnaires of the Italian version of Gastrointestinal Symptom Rating Scale
(GSRS, a 15-item survey scored according to a 7-point Likert scale) were mailed to all patients
responding to baseline questionnaire at 3 and 6 months, and to a cohort of unaffected controls,
living in the same geographical area, at 6 months after the outbreak. The GSRS item were grouped
in fi ve dimensions: abdominal pain, refl ux, indigestion, diarrhea, and constipation. At month 12,
all patients and controls were interviewed by a health assistant to verify Rome III criteria of IBS.
Student ’ s t -test and χ 2 - or Fisher ’ s exact test were used as appropriate.
RESULTS: Baseline questionnaires were returned by 348 patients: mean age ± s.d. (45 ± 22 years), 53 % female.
At outbreak, nausea (scored ≥ 4), vomiting, and diarrhea lasting 2 – 3 days or more were reported by
66, 60, and 77 % of patients, respectively. A total of 50 % reported fever and 19 % reported weight
loss (mean 3 kg). Follow-up surveys were returned at month 6 by 186 patients and 198 controls:
mean GSRS score was signifi cantly higher in patients than in controls for abdominal pain, diarrhea,
and constipation. At month 12, we identifi ed 40 patients with a new diagnosis of IBS (Rome III
criteria), in comparison with 3 subjects in the control cohort ( P < 0.0001; odds ratio 11.40; 95 %
confi dence intervals 3.44 – 37.82). The 40 cases of PI-IBS were subtyped according to the predominant
stool pattern as follows: 4 IBS with constipation, 7 IBS with diarrhea, 16 with mixed IBS, and
13 with unsubtyped IBS.
CONCLUSIONS: Our study provides evidence that Norovirus GE leads to the development of PI-IBS in a substantial
proportion of patients (13 % ), similar to that reported after bacterial GE.