Risk factors for sporadic Giardia infection in the United States: a case-control study in two FoodNet sites Open Access
Reses, Hannah Eve (2016)
Background: Giardia intestinalis is the most common intestinal parasite of humans in the United States, with an estimated 1.2 million cases of giardiasis occurring annually. Over 99% of cases in the United States are sporadic (i.e., not associated with a known outbreak), but the risk factors for sporadic giardiasis are not well described.
Methods: The Colorado and Minnesota sites of the Foodborne Diseases Active Surveillance Network (FoodNet) conducted a case-control study in 2003 and 2004 to assess risk factors for sporadic giardiasis. Cases were patients with non-outbreak-associated laboratory-confirmed Giardia infection reported to the FoodNet sites, and controls were matched by age and site. We used bivariate and multivariable logistic regression models to estimate the association between Giardia infection and exposures during the two week period prior to illness onset in case-patients. Population attributable fractions (PAF) were also calculated.
Results: Overall, 199 case-patients and 381 controls were enrolled. In the multivariable analysis, risk factors for Giardia infection included international travel (OR=13.7; 95% CI=4.7, 39.6; PAF=11.2%), drinking water from a river, lake, stream, or spring (OR=6.3; 95% CI=2.0, 19.9; PAF=9.3%), swimming in a natural body of water (OR=3.2; 95% CI=1.5, 6.8; PAF=10.4%), having high-risk sexual contact (OR=5.4; 95% CI=2.5, 11.5; PAF=10.2%), taking antibiotics (OR=2.6; 95% CI=1.3, 5.2; PAF=6.5%), and having a chronic gastrointestinal condition (OR=1.9; 95% CI=1.2, 3.1; PAF=13.3%). Eating raw vegetables or fruit was inversely associated with infection (OR=0.3; 95% CI=0.1, 0.8). Among individuals without a history of international travel during the exposure period, contact with children in diapers was a risk factor for giardiasis (OR=1.7; 95% CI=1.0, 2.7; PAF=17.9%).
Conclusions: This study provides additional evidence supporting previously reported protective and risk factors and identifies novel risk factors and host-level characteristics that deserve attention. Our results also highlight the importance of domestic exposures for sporadic giardiasis, as less than 12% of the illness was attributable to international travel. Giardia control measures should focus on decreasing exposure to unsafe drinking and recreational water and preventing person-to-person transmission via contact with children in diapers and sexual contact.
Table of Contents
1.6 Tables and Figures...36
2. Appendix: Case Questionnaire...46
About this Master's Thesis
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