Abstract
BackgroundMalaria in highland areas of Kenya affects children and adults. Local clinicians include symptoms other than fever when screening for malaria because they believe that fever alone does not capture all cases of malaria.MethodsIndividuals who presented to dispensaries in a highland Kenya site of low, unstable malaria transmission from 2007–2011 with 1 or more of 11 symptoms were tested by microscopy for malaria. Clinical malaria was defined as asexual Plasmodium falciparum infection on peripheral blood smear in an individual with any screening symptom. Asymptomatic P. falciparum infection was assessed in a cohort at ten time points to determine the extent to which symptomatic episodes with parasitaemia might be attributable to baseline (asymptomatic) parasitaemia in the community.Results3,420 individuals were screened for malaria, 634 < 5 years of age and 2,786 ≥ 5 years of age. For the diagnosis of clinical malaria, the symptom of fever had a sensitivity and specificity of 88.9% and15.4% in children <5 years, and 55.8% and 54.4% in children ≥5 years, respectively. Adding the symptom of headache increased sensitivity to 94. 4% in children <5 years and 96.8% in individuals ≥5 years, but decreased specificity to 9.9% and 11.6%, respectively, and increased the number of individuals who would be tested by 6% and 92%, respectively. No combination of symptoms improved upon the presence fever or headache for detection of clinical malaria. In the cohort of asymptomatic individuals, P. falciparum parasitaemia was infrequent (0.1%).ConclusionIn areas of low, unstable malaria transmission, fever is a sensitive indicator of clinical malaria in children <5 years, but not in older children and adults. Adding headache to fever as screening symptom increases sensitivity of detection in individuals ≥5 years old at the cost of decreased specificity. Screening for symptoms in addition to fever may be required to accurately capture all cases of clinical malaria in individuals ≥5 years old in areas of low malaria transmission.
Highlights
Malaria in highland areas of Kenya affects children and adults
From 2007 to 2011, 3,420 individuals were screened for malaria, and P. falciparum parasitaemia was detected in 224 individuals (6.5%), including 36/634 children
Findings for clinical malaria defined as symptomatic P. falciparum parasitaemia with measured fever are summarized in Additional files 1 and 2
Summary
Malaria in highland areas of Kenya affects children and adults. Local clinicians include symptoms other than fever when screening for malaria because they believe that fever alone does not capture all cases of malaria. Kipsamoite and Kapsisiywa experienced an atypical situation in 2007, when widespread indoor residual spraying (IRS) with long-lasting insecticides and introduction of artemisinin combination therapy with artemether-lumefantrine (Coartem©) led to a 14-month period with no clinical cases of malaria and possible interruption of malaria transmission [10] After this period, asymptomatic parasitaemia has been infrequent in these communities, providing a unique opportunity to study the sensitivity and specificity of fever and other symptoms for P. falciparum parasitaemia, which at this point occur almost exclusively in individuals with symptoms that lead them to seek evaluation and treatment at the health dispensaries on site. Sensitivity and specificity of individual symptoms and combinations of symptoms for alternate definitions of clinical malaria were assessed, including: (1) P. falciparum parasitaemia with measured fever (axillary temperature ≥37.5°C), (2) P. falciparum parasitaemia ≥ 1,000 parasites/μL with measured fever, or (3) P. falciparum parasitaemia ≥ 4,000 parasites/μL with measured fever
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