Background: Infection with Giardia lamblia is a common cause of diarrheal disease in the developing and industrialized world. Aims: We aimed to assess the prevalence of giardiasis in the United States (US) among patients with duodenal biopsies, investigating demographic and clinical factors associated with this condition. Methods: We conducted a cross-sectional study of patients with duodenal biopsies submitted to a national pathology laboratory between January 2, 2008, and December 31, 2015. The prevalence of giardiasis was calculated and categorized by the following patient sociodemographic and clinical data: age, sex, ethnicity, endoscopy indication, season, year, urban–rural setting, region, and presence of H. pylori and atrophic gastritis. Results: Among all patients (n = 432,813), the mean age was 52.2 years. The prevalence of giardiasis was 0.11%. Patients with giardiasis were more likely to be male (57.8 vs. 34.1%, p < 0.0001). Among patients who had a gastric biopsy (n = 363,788), those with giardiasis were more likely to be colonized with H. pylori (25.7 vs. 9.4%, p < 0.0001). There was no statistically significant association with age, endoscopy indication, urban–rural setting, ethnicity, season, or the presence of atrophic gastritis. On multivariate analysis, male sex, Southern region, and the presence of H. pylori were independently associated with giardiasis. Conclusions: To our knowledge, this is the largest study to date to assess predictors of giardiasis in the US. We found that male sex, being colonized with H. pylori, and residing in the Southern US are independently associated with giardiasis infection.
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