The prolonged and pervasive stress of the COVID-19 pandemic has resulted in a substantial global mental health burden. Existing research has shown that the resulting psychopathology often spans multiple diagnostic categories within the DSM-5 and ICD-11 systems, complicating clinical management and raising concerns about overdiagnosis and the overuse of "comorbidity." This has led to a debate about diagnostic approaches, with a transdiagnostic approach gaining traction as a potential solution. This study aimed to test the transdiagnostic hypothesis by examining psychiatric data collected during the first wave of the pandemic in two different countries—Italy and Israel—using distinct survey methodologies. The researchers hypothesized that the identified patterns of complex symptomatology would be consistent across both populations, providing stronger support for a transdiagnostic framework.

The literature review examined the use of the term "transdiagnostic" within the context of the COVID-19 pandemic. A significant number of studies employed this term, but often in a general way, without precise specification of symptom associations relevant to diagnosis. Most research focusing on transdiagnostic approaches to treatment related to known comorbidities such as the association between depression and anxiety. Fewer studies investigated three or more associated symptoms, highlighting the unique contribution of the current research. The review identified a need for an empirical approach to accurately understand the mental health impact of the pandemic, leading to more accurate diagnostic categories, improved treatment planning, and necessary organizational modifications.

The study involved two independent studies: one conducted in Israel and one in Italy. The Israeli study consisted of three cross-sectional surveys using different sampling methods, examining various symptom combinations. The Italian study was a cross-sectional web-based observational study conducted during the country's first COVID-19 peak, using convenient sampling via Facebook advertisements. The surveys employed various validated psychometric scales, including the Global Psychotrauma Screen (GPS) post-traumatic stress symptoms (PTSS) subscale, the 9-item Patient Health Questionnaire (PHQ-9) for depression, the 7-item Generalized Anxiety Disorder scale (GAD-7), the GPS-Post-Traumatic Stress Disorder-Negative Affect (PTSD-NA) scale, and the Perceived Stress Scale (PSS). Data analysis involved analyzing the frequency of symptom combinations, identifying the most prevalent patterns, and using proportion tests to compare various subgroups (Italians vs. foreigners, individuals with and without prior psychiatric history). The analyses employed Bonferroni corrections for multiple comparisons.

Both the Israeli and Italian studies revealed significant correlations between pairs of symptoms. The Israeli surveys showed a consistent pattern of symptom clustering, with a high prevalence of combinations including depression, anxiety, and loneliness in the first survey, and phobia, anxiety, and depression in the subsequent surveys. The prevalence of these combinations increased over time across the three surveys. In the Italian study, the most frequent symptom combinations included post-traumatic stress symptoms (PTSS), depression, and PTSD-NA; and anxiety, PTSS, depression, and PTSD-NA. The five-symptom combination (anxiety, perceived stress, PTSS, depression, and PTSD-NA) showed the highest prevalence, significantly exceeding the prevalence of the three- and four-symptom combinations. Individuals with a prior history of psychiatric illness showed a significantly higher likelihood of experiencing multiple symptoms compared to those without such history. While some differences emerged between Italian and foreign participants in the prevalence of three-symptom combinations, these differences were less pronounced for the four- and five-symptom combinations.

The findings from both the Israeli and Italian studies support the existence of a complex transdiagnostic symptomatology pattern during the first COVID-19 surge, irrespective of survey methodology or ethnic background. The high correlation between symptom severity suggests a common underlying disorder, rather than simply multiple comorbid diagnoses. The pattern's association with pre-existing psychiatric vulnerability and the increased prevalence over time point toward a cumulative effect of prolonged stress. This evidence strongly supports the need for a broader, transdiagnostic approach to understanding and treating COVID-19-related mental health consequences. The findings also lend credence to the concept of "COVID Stress Syndrome", a transdiagnostic condition that transcends DSM-5 and ICD-11 categories. This transdiagnostic perspective is crucial for developing effective prevention and treatment programs in the post-COVID era, especially considering the potential for multiple stressors and complex symptom presentations.

This binational study provides robust evidence for a transdiagnostic approach to understanding the mental health consequences of the COVID-19 pandemic. The consistent pattern of complex symptom clusters across different populations and methodologies highlights the need for moving beyond traditional diagnostic categories. A transdiagnostic framework offers a more accurate and comprehensive characterization of COVID-19-related psychopathology. Further research is needed to refine diagnostic criteria and develop targeted interventions for this condition, encompassing the broader neuropsychiatric spectrum.

The study's limitations include the lack of assessment of the full neuropsychiatric spectrum (including long COVID symptoms), a modest sample size in the Israeli study compared to the Italian study, and the focus on data from the first pandemic surge. Despite these limitations, the convergence of findings across two different countries and methodologies strengthens the study's overall conclusions.