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Risk factor analysis for unfavorable outcone in adult patients with imported plasmodium falciparum malaria ; A retropsective study

(2016) Olijve, S.J.

Background: Malaria remains to be one of the major causes for morbidity and mortality worldwide, particularly if it is caused by Plasmodium falciparum. Given the low case-fatality rates of malaria in non-endemic countries, studies on severe disease in imported malaria frequently used the World Health Organization (WHO) criteria instead of mortality to define their (surrogate) endpoint severe malaria. However, when used in this way, defining criteria for severe malaria are also used as explanatory variables and they will lose their independent character in the analysis. The aim of the present study was to explore the relative contribution of traditional risk factors for severe disease in imported Plasmodium falciparum malaria by using an alternative outcome measure: ‘unfavourable outcome’. Additionally, the prognostic value of plasma lactate on admission was investigated.
Methods: All adult patients who were diagnosed with P. falciparum malaria in the Havenziekenhuis, Rotterdam from 2000-2015 were included in the analysis. Primary outcome measure was an unfavourable outcome, defined as hospitalization ≥ 5 days, admission to intensive care unit (ICU), referral for dialysis and/or mortality. Using multivariable logistic regression, prognostic factors for an unfavourable outcome were identified.
Results: 442 cases of P. falciparum malaria were evaluated; 140 (31.7%) had an unfavourable outcome. Odds ratio (OR) for an unfavourable outcome was 2.3 (95% CI 1.13-4.83) for patients with a thrombocyte count below 50 x 109/L on admission. For each 1 mmol/L increment of plasma lactate, odds for an unfavourable outcome rose with 1.88 (95% CI 1.26-2.81). OR for an unfavourable outcome was 3.82 (95% CI 1.78-8.21) for cases with a parasite load exceeding 100,000 parasites/μL on admission. Plasma lactate had a diagnostic performance equivalent to the performance of the parasite load. WHO-defined severe malaria had an OR of 30.05 (95% CI 12.50-72.27) for an unfavourable outcome.
Conclusion: A thrombocyte count below 50 x 109/L, an increased level of plasma lactate and a parasite load exceeding 100,000 parasites/μL at initial presentation are independent predictors of an unfavourable outcome in adult patients with imported P. falciparum malaria. Plasma lactate levels taken on admission had a diagnostic value for unfavourable outcome comparable to that of the parasite load but the advantage that it is less time-consuming and technician-dependent than determination of the parasite load. The endpoint unfavourable outcome was found to correlate highly with WHO-defined severe malaria. Given the low prevalence of malaria among ill-returned travellers, the abovementioned prediction parameters will foremost be used for its high negative predictive value, i.e. to rule out an unfavourable outcome on admission in the returned traveller.

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