Generalized anxiety disorder and associated factors in adults in the Amazon, Brazil: A population-based study

Background: The purpose of this study was to assess the prevalence and associated factors of generalized anxiety disorder (GAD) in adults using the seven-item GAD scale (GAD-7) and to evaluate the properties of the two-item (GAD-2) as a population screening tool. Methods: We carried out a cross-sectional population-based study in the Manaus Metropolitan Region in 2015, Brazil. Adults aged 18 years or more were eligible to participate. We performed probabilistic three-phase sampling and collected sociodemographic and clinical variables. Descriptive statistics and a Poisson regression with robust variance with corrections for complex sampling were used. The accuracy of GAD-2 was assessed using GAD-7 as the gold standard. Results: We included 4001 participants. The prevalence of GAD was 8.4% (95% confidence interval 7.6-9.4%) and was significantly associated with self-reported poor health status and presenting depressive symptoms (p < 0.01). GAD-2 sensitivity was 63.9%, and its specificity was 97.4%. Limitations: Because of the cross-sectional design of the study, the results are prone to reverse causality and recall bias. The surveyed people were not questioned about their medical diagnosis of anxiety, access to mental health services, or alcohol, tobacco or other drug use. The screening tools were not validated in the Brazilian or Amazon population. Conclusion: About eight in 100 adults living in Manaus presented GAD, and it is more prevalent among people with a poorer health status and depression. Because of its low sensitivity, GAD-2 is not useful as a screening tool.