Twenty-Year Trends in Malaria Epidemiology, Importation Dynamics, and Surveillance in Oman: A Retrospective National...

Malaria remains a major vector-borne disease worldwide. Oman interrupted endemic malaria transmission in 2010, but imported infections and occasional locally acquired cases continue to require sustained surveillance. This study evaluated national malaria epidemiology and surveillance patterns across the complete 2005-2024 period.

We conducted a retrospective observational analysis of aggregated malaria surveillance indicators reported by the Oman Ministry of Health and linked national surveillance sources. The analytical series comprised 20 consecutive annual observations (2005-2024). Indicators included Annual Parasite Incidence (API), Slide Positivity Rate (SPR), Annual Blood Examination Rate (ABER), blood slides examined, case origin, surveillance approach, Plasmodium species distribution, and 2024 governorate-level case counts. Descriptive analyses, linear temporal models, robust Poisson rate models, regression diagnostics with Newey-West sensitivity analyses, and a 2024 population-referenced geographic analysis were performed.

Across all 20 years, 17,080 malaria cases were reported; 16,905 (98.98%) were imported, 174 (1.02%) were autochthonous, and one case was unclassified by origin. API declined from 0.217 per 1000 population in 2005 to 0.064 in 2024. ABER and annual blood-slide examination volume declined, whereas SPR increased over time. The temporal slope for blood slides examined was strongly negative (standardized β = -0.907, p < 0.001). The annual testing-volume-SPR association was inverse and statistically significant in the restored 20-year series (B = -0.00000147, 95% CI -0.00000254 to -0.00000040, p = 0.010; R² = 0.317); the association remained significant with Newey-West lag-1 standard errors (p = 0.019). Among the two principal species, the relative annual rate of P. falciparum increased (aRR = 1.142, 95% CI 1.068-1.221, p < 0.001), whereas that of P. vivax decreased (aRR = 0.952, 95% CI 0.919-0.987, p = 0.007). In 2024, crude reported case rates varied across governorates, but these rates combine imported and locally acquired cases and therefore do not represent local transmission incidence.

Surveillance during 2005-2024 was characterized by persistent predominance of imported malaria, sparse autochthonous cases, changing species composition, and declining testing-volume indicators. The findings support continued diagnostic readiness and surveillance for imported infection and possible re-establishment, without implying effectiveness of any specific intervention.