Clinical Spectrum and Admission Correlates of Complicated Imported Malaria in Polish Travellers: An 11-Year Retrospective Analysis with Geographic Mapping of Travel Destinations.

Background: Complicated malaria occurs in 15-40% of hospitalised imported cases, and European centres often define it more broadly than the WHO 2023 severe-malaria criteria, which, calibrated for semi-immune populations, may under-identify severe disease in non-immune travellers; Central and Eastern European data are limited. We examined the clinical spectrum, travel destinations, and admission correlates of complicated imported malaria in non-immune Polish travellers. Methods: This was a two-centre, 11-year retrospective cohort of 93 laboratory-confirmed episodes in 91 adults (December 2014-October 2025). Complicated disease was a composite of organ-specific complications on admission. We derived the exploratory nine-item IMSC-NIT severity-capture criteria, with a pre-specified analysis restricted to the four items not overlapping the outcome (age, C-reactive protein, procalcitonin, platelets). Results: Complicated disease affected 31/93 episodes (33.3%), exceeding the 10/93 that met the strictly assessable WHO criteria. Plasmodium falciparum predominated; 88.2% with documented status had used no chemoprophylaxis; age was the only independently associated variable (multiple-imputation odds ratio 1.07 per year, 95% CI 1.02-1.11). The restricted four-item score gave an area under the curve of 0.76 (95% CI 0.65-0.85; optimism-corrected 0.72). Conclusions: The WHO criteria alone may miss non-immune travellers with organ involvement at presentation. The IMSC-NIT is a hypothesis-generating severity-capture aid requiring external validation before clinical use.