This study is a retrospective review of clinical and laboratory records from hospital databases. Case files for children 0-14 years old admitted to any of the ICUs with a suspicion of malaria between January 2004 to December 2009 were reviewed for: (1) ICU logbooks (in which demographic data from each admitted patient, a presumptive diagnosis at admission and a final diagnosis at discharge are systematically registered), (2) hospital laboratory logbooks (in which the semi-quantitative results of TBSs performed in each hospital are systematically registered), and (3) SIVEP-Malaria (the National Malaria Information System available on-line, which registers results of TBSs performed in each reporting unit such as the hospitals of interest). Cases were included if there was evidence of malaria diagnosis by microscopy in any of the three information systems searched. The study enrolled only patients after 2004 because of better reliability of the National Malaria Information System (SIVEP-Malaria) and access to the clinical files, avoiding retrieval bias.
As comparators, clinical and laboratory data from children of the same age group admitted between January 2009 and July 2010 to the Fundacao de Medicina Tropical Dr. Heitor Vieira Dourado with a diagnosis of malaria were retrieved electronically from the computerized hospital records system (iDoctor ) and reviewed. With the exception of automated full blood count, routinely requested for all these hospitalized children, more specific laboratory tests (such as biochemistry and arterial gas analysis) were requested only if clinical symptoms were suggestive of complications. As part of routine follow-up, all malaria admitted children were reassessed in the Outpatient Clinics seven days after discharge to guarantee adequate clinical and parasitological follow-up.
TBSs are routinely performed for the diagnosis of malaria in Brazil, prepared as recommended by the Walker technique and evaluated by a local microscopist. The results of peripheral parasitemia are given using the following semi-quantitative system: 1/2+ (200-300 parasites/mm3); 1+ (301-500 parasites/mm3); 2+ (501-10,000 parasites/mm3); 3+ (10,001-100,000 parasites/mm3); and 4+ (>100,001 parasites/mm3). The cut-off to define high parasitemia (in the final analysis) was based on the distribution of semi-quantitative parasitemia results. All positive slides and 10% of negative slides are routinely reviewed in a reference unit with experienced microscopists. In case of divergence, the reviewed result is updated in the on-line system. PCR diagnosis for malaria was not routinely performed in these patients. Only children with a positive TBS for Plasmodium spp. are treated according to the Brazilian Anti-Malarial Treatment Guidelines, which recommends chloroquine (25 mg/kg over 3 days)+primaquine (0.5 mg/kg/day over 7 days) for P. vivax infection and artemether/lumefantrine for 3 days for non-severe P. falciparum infection. Severe P. falciparum infections are treated with parenteral artemether or artesunate for 7 days.
Data for each admitted individual was systematically retrieved from the medical charts by the same member of the study team, and included the following variables: sex, age, malarial species, semi-quantitative parasitemia, duration of disease (in days) prior to the admission to the ICU or ward, outcome, presence of a given acute co-morbidity other than malaria or a chronic disease confirmed through a reliable diagnostic method, and presence of any WHO-defined severe malaria criteria. Briefly, WHO criteria for severe falciparum malaria validated for adults and children include: (1) impaired consciousness or unrousable coma (Blantyre coma scale <=2 or Glasgow coma scale <=10); (2) prostration, i.e. generalized weakness such that the patient is unable to walk or sit up without assistance; (3) failure to feed; (4) multiple convulsions (greater than two episodes in 24 h); (5) respiratory distress defined as the presence of deep (acidotic) breathing or retractions; (6) circulatory collapse or shock, systolic blood pressure <50 mmHg (algid malaria) and/or need for vasopressor support; (7) clinical jaundice or total bilirubin >3 mg/dL; (8) hemoglobinuria (blackwater fever); (9) abnormal spontaneous bleeding (disseminated intravascular coagulation); (10) pulmonary edema (radiological); (11) hypoglycemia (blood glucose <40 mg/dL); (12) metabolic acidosis (plasma bicarbonate <15 mmol/L); (13) severe anemia (Hb<5 g/dL); (14) hyperlactatemia (lactate >5 mmol/L); or (15) acute renal failure (serum creatinine >3 mg/dL). Acute respiratory distress syndrome (ARDS) was defined as acute bilateral lung infiltrates in chest X-rays, and a PaO2:FiO2<200 mmHg. The data retrieved were reviewed by another member of the study team and discrepancies resolved by a third member if necessary.
In all ICUs, collection of venous blood samples for aerobic culture and arterial blood for gas analysis was routinely carried out on admission prior to administration of antibiotics. From all the patients hospitalized in the ICU, the Pediatric Index of Mortality (PIM) score was calculated with data from the first hour of admission, based on the systolic blood pressure, pupillary reactions to bright light, PaO2, FiO2, base excess in arterial blood, need for mechanical ventilation at any time during the first hour in ICU, elective admission, and presence of concomitant diagnoses. Severity was defined in the presence of at least one of the aforementioned WHO severity criteria. As blood gas analysis samples were not systematically collected for patients not admitted to the ICU, hyperlactatemia and metabolic acidosis were not used to classify severity nor assessed as a risk factor associated with ICU admission. The disease was classified as being directly caused by plasmodial infection if no other cause was identified and no concurrent acute or chronic diseases were confirmed.
Data were analyzed using SPSS  version 16.0 for Windows (SPSS Inc.  Chicago, IL, USA). Proportions of fatality were compared by Fisher exact test (corrected by Yates' test if necessary); differences were considered statistically significant for p<0.05. The crude Odds Ratio (OR) with its respective 95% Confidence Interval (95% CI) was determined considering the admission to ICU as the dependent variable. Logistic regression was used for the multivariate analyses and the adjusted Odds Ratios with 95% CI were also calculated. A multivariate logistic regression was performed with admission to the ICU as the outcome, using an automated backward and forward stepwise estimation. All variables that were associated with admission to the ICU at a significance level of p<0.10 in the univariate analysis were included in the multivariate analysis. Statistical significance was considered if p<0.05 in the Hosmer-Lemeshow goodness-of-fit test.