Longitudinal, Multimodal Assessment of Anomalous Health Incidents among Canadian Personnel: Questionnaire, Clinical, and Biomarker-Based Approaches

Abstract

In late 2016, Canadian and U.S. government personnel stationed in Havana, Cuba, started reporting sudden-onset neurological symptoms, later classified as anomalous health incidents (AHIs). These events had a profound impact on the lives of those affected and proved difficult to diagnose. To investigate the symptom profiles, underlying risk factors, physiological correlates, and potential causes of AHIs, we conducted a longitudinal mixed-methods cross-sectional study involving 51 participants, comprising a total of 229 assessments. Data collection included symptom questionnaires, biological sampling, cognitive testing, electrophysiological recordings, and neuroimaging. Approximately half of the participants reported high symptom burden, primarily encompassing headaches, difficulty concentrating, fatigue, memory deficits, and irritability. Some participants had increased symptoms of anxiety, depression, sleep dysfunction, headaches, post-traumatic stress disorder, and post-concussive symptoms as measured by validated questionnaires. The AHI experiences correlated most with post-concussion symptoms as identified by the Rivermead Post-Concussion Symptoms Questionnaire (RPQ). Risk factors for high symptom burden included pre-existing endocrine conditions and elevated anxiety scores at baseline. Blood analyses revealed elevated levels of thyroid-stimulating hormone (TSH) in a subset of participants during Cuba deployment. Neuropsychological testing identified cognitive weaknesses in multi-tasking and problem-solving. Although standard electrophysiological recordings and neuroimaging did not reveal overt pathology, research-based methods identified blood-brain barrier disruption and cortical slowing in some individuals. These findings point to a potential environmental origin, with mass fumigation in Havana identified as a contributing cause. The evidence presented calls for coordinated public health, clinical, and policy responses to mitigate the neurological risks of chemical pesticide overexposure in the future.