Background: Diverse presentations in long covid and why it occurs in ?selected cases? only not known

Methods: Prospective, observational study of 8000 COVID 19 RT PCR confirmed hospitalised cases attending rehabilitation unit post discharge. Clinical & immunological phenotypes were categorised in four types, Duration of illness (DOI) classified into transient or evolved, persistent, progressive, Topographical classification into vague or nonspecific and systemic or organic as per involvement of organ systems, Treatment responsive classified as per treatment response into easy to treat and difficult to treat or refractory to treatment, & Fourth is according genetic makeup patterns or strain patterns observed in first, second and third wave as pulmonary, extrapulmonary and pulmonary-extrapulmonary combo. Investigated with LDH, Uric acid, CRP, D-dimer, antinuclear antibody, retrospective analysis as antigenic cross reactivity, inflammatory markers and interventions required during hospitalization including follow up HRCT thorax in selected cases.

Results: Clinical phenotypes as per DOI & Topographical phenotypes has documented significant association with immunological markers (p<0.00001) Treatment response phenotypes has documented significant association with DOI before hospitalisation, interventions required and inflammatory marker(p<0.00001) Clinical phenotypes in three waves has documented significant association with four pathophysiological pathways(p<0.00001)

conclusion: 'Sequential titers' of immunological markers can predict occurrence of long covid and timely interventions will have positive outcome in those selected cases.