The present study was performed as a sub-study of “Severe Malaria in African Children II” (SMAC) (registered at PACTR201102000277177). The study and the sub-study have been approved by the local ethic committees in Kumasi, Ghana; Kisumu, Kenya; and Lambaréné, Gabon. The studies have been performed in three study sites: Komfo Anokye Teaching Hospital, Kumasi, Ghana; Centre de Recherche Mèdicale de Lambaréné, Lambaréné, Gabon; and Kenya Medical Research Institute, Kisumu, Kenya. Guardian informed consent was obtained from all participants.
The study was designed as a prospective multicenter cohort study, comparing OAE measured in children with severe malaria to a healthy, local, age-matched control population. The malaria cohort was divided into a severe malaria group and a cerebral malaria group. OAE were measured in the control group once. In the malaria groups they were measured at the following time points: immediately after diagnosis of severe malaria prior to starting medication, 12–24 h after the first medication, after recovery, 3–7 days post diagnosis, and 14–28 days after the diagnosis. OAE were considered as absent if the reproducibility was below 60 %.
The healthy control population was recruited at the study sites outside the hospital in schools and kindergartens. Children aged up to 10 years with no medical history of hearing impairment and no history of fevere related admission to hospital as an in-patient qualified for the control group . No further clinical or laboratory examination was performed.
The severe malaria group was selected according to the following parameters: children up to 10 years; a diagnosis of Plasmodium falciparum malaria confirmed with a minimum parasitemia of >5000 parasites/μL on the initial blood smear; asexual forms of P. falciparum; and clinical manifestations that required hospitalization, like hyperlactatemia or metabolic acidosis, severe anemia, dark urine, hypoglycemia, jaundice, respiratory distress, severe vomiting, shock, abnormal bleeding, and/or renal failure [19–21]. Antimalarial treatment within 24 h prior to admission was an exclusion criterion.
Cerebral malaria was defined as severe malaria with neurological signs and symptoms like coma with a Blantyre Coma score of ≤ 2, repeated generalized seizures, focal neurological findings, or prostration . Prostration was defined by the presence of one or more of the following symptoms: not being able to breastfeed, sit, stand, or walk depending on the age of the child . Fundoscopy was not done.
For all groups, the ear inspection had to show a transparent tympanic membrane. Children with pathologic findings in the ear canal did not qualify. The baseline OAE testing was done immediately after confirmation of severe or cerebral malaria.
Further clinical and laboratory examinations were performed in the severe malaria and the cerebral malaria group at the time of inclusion in the study. On admission the vital signs—heart rate, temperature, respiratory rate—were documented. The following clinical and laboratory parameters were examined: respiratory distress, deep breathing, severe vomiting, prostration, coma, repeated generalized seizures, jaundice, parasitemia, hemoglobin, platelets, glucose, creatinine, alaninaminotransferase, bilirubin, glucose, hemoglobinuria.
As part of the SMAC II study, all patients were treated with parenteral artesunate after the first baseline measurement. The total dose of artesunate was 12 mg/kg, given as five intramuscular injections of 2.4 mg/kg at 0, 12, 24, 48, and 72 h or as three injections of 4 mg/kg at 0, 24, and 48 h either intramuscularly or intravenously. Allocation to one of the three schedules was random. Upon discharge patients received a weight-adapted standard regimen of artemether and lumefantrine .
Otoacoustic emissions measurement
The OAE measurements were performed at each study site by two operators. Transient OAE were measured using a Madsen Capella Otoacoustic emissions machine (Otometric, Taastup, Denmark). Both ears were measured five times and the best result was taken. If the reproducibility was below 60 % on one ear the OAE were considered absent. Each measurement consisted of 2080 repetitions. A broadband click ranging from 1 kHz to 4 kHz for 2 ms was used as a stimulus. The measurement was considered of a poor quality if the rejection rate exceeded more than 2000 sweeps. Therefore measurements were excluded with more than 2000 rejected sweeps. If the measurement at baseline did not work, the OAE testing was abandoned, and the treatment of the severely sick child immediately initiated. A second try was performed at the other measurement time points.
Otoacoustic measurements with a reproducibility below 60 % on one ear or both ears were considered a fail. Demographic and clinical data were compared between groups depending on data type and distribution either by Student’s t-test or Mann–Whitney U test for continuous variables and by chi-square test or Fisher’s exact test for proportions as appropriate. The proportions of patients passing the OAE test were compared between groups (malaria vs control or the different treatment regimens respectively) by chi-square test. The study collective was categorized into severe non-cerebral malaria and cerebral malaria and statistically compared as described above. In order to identify prognostic factors for failing the OAE test at last follow-up, a univariate comparison of admission data was done between patients failing and patients passing on the last follow-up as described above. Variables with association at a significance level of p < 0.05 in the univariate analysis were entered into a stepwise logistic regression model with conditional forward selection as the selection method and age and sex as mandatory variables. The statistical evaluation was done by IBM SPSS statistics 21 (New York, NY, USA).