Prognosis of isolated hyperparasitemia in adults with imported severe malaria

Hyperparasitemia (HP), defined as a parasitemia > 4%, is the most frequent severity criterion considered in adults with imported malaria. Isolated hyperparasitemia (iHP), accounting for 10-40% of cases, has a controversial prognostic significance.

Multicenter retrospective study including all adult patients with imported Plasmodium falciparum malaria and HP admitted to 16 hospitals in the Greater Paris area between 2018 and 2022 and reported to the National Reference Center. Amongst HP patients, iHP at hospital admission was identified by retrospective analysis of medical records to minimize classification bias. The primary endpoint was a composite outcome using the Desirability of Outcome Ranking (DOOR) method with three levels of decreasing desirability: hospital survival, absence of organ support requirement, shortest length of stay. Association between HP, iHP and outcomes was evaluated by negative binomial regression models.

Of 355 patients enrolled with HP, 135 (38%) had iHP. iHP patients were predominantly male (55.6%), aged 41 (32-52.3) years and born in an endemic country (86.4%). Compared with patients with HP and additional severity criteria, iHP was independently associated with a lower risk of worse DOOR [RR 0.56, 95%CI (0.48-0.65)]. No deaths were recorded in the iHP population, and 2/135 (1.5%) patients required organ support. In the iHP population, immunosuppression [RR 1.65, 95%CI (1.16-2.37)] and parasitemia>10% [RR 1.57, 95%CI (1.01-2.24)] were independently associated with worse DOOR. Only 47 (34.8%) iHP patients were admitted to an ICU at diagnosis, and 40 (29.6%) were treated with oral therapy alone.

In imported malaria in France, iHP was associated with a low risk of serious adverse outcomes overall. In patients with iHP, immunosuppression and parasitemia >10% were associated with an increased risk of adverse outcome, highlighting the importance of a close hospital monitoring.