Table.
Germ theory and COVID-19-CSS as threshold concepts in medicine
| Description of criterion for a threshold concept | Germ theory | COVID-19-CSS | |
|---|---|---|---|
| Transformative | The learner or practitioner's understanding of a subject is transformed; the threshold concept is a portal of entry into a new, previously inaccessible way of thinking about the subject | Specific microbes cause specific diseases transformed the 19th century understanding of transmissible disease | Treating the maladaptive host immune response in addition to the microbe is a transformative concept |
| Troublesome | Involves knowledge that is often alien, confronting, or counterintuitive; drastically alters one's perception of how that piece of the world works | That microscopic organisms are responsible for human disease | Immunosuppression in acute infection is counterintuitive, and on the surface, contradicts traditional medical teaching |
| Irreversible | Once learned, a threshold concept cannot be unlearned. Subject experts might not recall their own difficulties in grasping a threshold concept and underestimate why it is problematic for novices | Theories such as miasmas (poisoned air) and abiogenesis (simple life arising from non-living material) receded | Ongoing work will refine the definition and treatment of COVID-19-CSS |
| Integrative | Brings together different aspects of the subject that previously did not seem (to the learner or practitioner) to be related. Connections between different subjects that were previously hidden are revealed | Koch's postulates integrated findings from Ehrlich, Löeffler, and others to establish a causative relationship between a microbe and a particular disease | Integrates established concepts (eg, EBV-HLH) with current concepts (COVID-19-CSS or COVID-19 hyperinflammation) |
| Bounded | The concept is limited by boundaries with other concepts and by disciplinary boundaries | Germ theory was inaccurately applied to other diseases such as Hodgkin lymphoma | Non-microbial CSSs (eg, GVHD, CART CRS) have limited applicability to COVID-19-CSS |
| Discursive | Crossing a conceptual threshold involves enhancement and extension of discipline-specific language | Numerous neologisms arose; microbiology, bacteriology, vaccines | COVID-19 cytokine storm syndrome; COVID-19 hyperinflammation; pathological immune activation |
| Reconstitutive | The learner or practitioner's understanding is reconfigured according to the new understanding | Helped usher in the modern era of scientific medicine | Identifying maladaptive immune responses will probably apply to other microbial diseases |
| Liminal | Learners occupy a transitional liminal space characterised by oscillation between old and new conceptual understandings | Germ theory was fiercely debated for many years before it was widely accepted | The entire discipline of medicine has been in a liminal space during the current pandemic, with ongoing controversies surrounding the definition and significance of COVID-19-CSS |
CSS=cytokine storm syndrome. EBV-HLH=Epstein-Barr virus-associated haemophagocytic lymphohistiocytosis. GVHD=graft-versus-host disease. CART CRS=chimeric antigen receptor associated cytokine release syndrome.