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In late 2010, an outbreak of Cryptosporidium hominis affected 27,000 inhabitants (45%) of Östersund, Sweden. Previous research shows that abdomen and joint symptoms commonly persist up to 5 years post-infection. It is unknown whether Cryptosporidium is associated with sequelae for a longer duration, how persisting symptoms present over time, and whether sequelae are associated with prolonged infection. In this prospective cohort study, a randomly selected cohort in Östersund was surveyed about cryptosporidiosis symptoms in 2011 (response rate 69.2%). A case was defined as a respondent reporting new diarrhoea episodes during the outbreak. Follow-up questionnaires were sent after 5 and 10 years. Logistic regressions were used to examine associations between case status and symptoms reported after 10 years, with results presented as adjusted odds ratios (aOR) with 95% confidence intervals. Consistency of symptoms and associations with case status and number of days with symptoms during outbreak were analysed using X 2 and Mann–Whitney U tests. The response rate after 10 years was 74% (n = 538). Case status was associated with reporting symptoms, with aOR of ~3 for abdominal symptoms and ~2 for joint symptoms. Cases were more likely to report consistent symptoms. Cases with consistent abdominal symptoms at follow-up reported 9.2 days with symptoms during the outbreak (SD 8.1), compared to 6.6 days (SD 6.1) for cases reporting varying or no symptoms (p = 0.003). We conclude that cryptosporidiosis was associated with an up to threefold risk for reporting symptoms 10 years post-infection. Consistent symptoms were associated with prolonged infection.

In 2010, a Cryptosporidium hominis outbreak resulted in 27,000 clinical cryptosporidiosis cases (45% of the population) in Östersund, Sweden. Long-term abdominal and joint symptoms are common following cryptosporidiosis in adults, and it can affect the development of children in low-income countries. We investigated the potential consequences for children in a high-income setting. In 2011, we prospectively surveyed 600 randomly selected children aged 0-5 years from Östersund. Cases were defined as respondents reporting new episodes of diarrhoea during the outbreak. After 10 years, respondents received a follow-up questionnaire about long-term symptoms (n = 423). We used X2 and Mann-Whitney U tests to assess between-group differences in demographics and the mean number of symptoms. Logistic regressions adjusted for sex, age, and prior issues with loose stools were used to examine associations between case status and symptoms reported at follow-up. We retrieved data on healthcare visits from patient records. In total, 121 cases and 174 non-cases responded to the follow-up questionnaire (69.7%). Cases reported 1.74 (median 1.00, range 0-14) symptoms and non-cases 1.37 (median 0.00, range 0-11) symptoms (p = 0.029). Cases were more likely to report joint symptoms (aOR 4.0, CI 1.3-12.0) and fatigue (aOR 1.9, CI 1.1-3.4), but numbers were generally low. We found no between-group differences in abdominal symptoms, healthcare utilization, or disease diagnoses. Children aged 0-5 years from high-income countries may experience long-term symptoms after cryptosporidiosis, but may not be affected to the same extent as adults or their peers living in low-income countries.

OBJECTIVES: In 2010, 27,000 inhabitants (45% of the population) of Östersund, Sweden, contracted clinical cryptosporidiosis after drinking water contaminated with Cryptosporidium hominis. After the outbreak, local physicians perceived that the incidence of inflammatory bowel disease (IBD), including ulcerative colitis (UC), Crohn's disease (CD), and IBD-unclassified, and microscopic colitis (MC) increased. This study assessed whether this perception was correct.

MATERIALS AND METHODS: This observational study included adult patients (≥18 years old) from the local health care region who were diagnosed with pathology-confirmed IBD or MC during 2006-2019. We collected and validated the diagnosis, date of diagnosis, age at diagnosis, and sex from the Swedish quality register SWIBREG and electronic patient records. Population data were collected from Statistics Sweden. The incidences for 2006-2010 (pre-outbreak) and 2011-2019 (post-outbreak) were evaluated by negative binomial regression analysis and presented as incidence rate ratios (IRRs). Data were analyzed for IBD, for UC and CD separately, and MC.

RESULTS: During the study period, we identified 410 patients with new onset IBD and 155 new cases of MC. Overall, we found a trend toward an increased incidence of IBD post-outbreak (IRR 1.39, confidence interval (CI) 0.99-1.94). In individuals ≥40 years old, the post-outbreak incidence significantly increased for IBD (IRR 1.69, CI 1.13-2.51) and CD (IRR 2.23, CI 1.08-4.62). Post-outbreak incidence of MC increased 6-fold in all age groups (IRR 6.43, CI 2.78-14.87).

CONCLUSIONS: The incidence of late-onset IBD and MC increased after the Cryptosporidium outbreak. Cryptosporidiosis may be an environmental risk factor for IBD and MC.