The study was carried out in Adeoyo State Hospital, Adegbite and Oni Memorial Children's Hospital, Ring-Road. Both hospitals are in Ibadan South West Local Government Area of Oyo State, Nigeria. Ibadan South West Local Government Area is situated between Latitude 7°21'2.48"N and Longitude 3°51'55.84"E (Fig. 1) and has a population of 282,585 as at 2006 census. Generally, Ibadan city is the third most populous city in Nigeria with over six million people. The climatic condition is typical of tropical regions which consists of both raining and dry seasons that spans through April to October and November to March respectively. The average annual rainfall is about 2100mm while the temperature is about 27oC. There are rivers running through the city of Ibadan which include Ogunpa, Kudeti and Ona river among others. The population consist of civil servants, traders, students, artisans and even farmers. While some of the residents live and settle in urban City of Ibadan, they still visit rural areas or their home village for some activities. Also, many people come from rural areas to Ibadan thereby hosting different people from various parts of the country. Nonetheless, Ibadan residents are predominantly of Yoruba ethnic group.
This is a hospital-based and randomized cross-sectional survey. Study was conducted from May to August 2019 in two different hospitals which are Adeoyo State Hospital, Adegbite and Oni Memorial Children's Hospital, Ring-Road, Ibadan. Samples were collected from individuals attending these hospitals and met the inclusion criteria. Criteria for inclusion include feelings of headache, fever with temperature greater than 38oC, completion of questionnaires, blood samples submission and willingness to provide written or oral informed consent. Those who decline to participate were excluded. Questionnaire was given to each subject to collect their data such as age, sex, occupation, education, use of mosquito nets, presence or absence of river within ≤1 Km participant’s home. Other data such as blood group and genotype were gotten from their medical records.
The sample size was computed using a previous malaria parasite prevalence of 78%  at a confidence interval (CI) of 95% and 5% margin of error following the formula of Araoye, 2014 for calculating sample size. This give rise to a total of 300 subjects that were recruited for this study.
Blood Collection and laboratory procedures
Samples of blood were obtained intravenously with the assistance of a trained Laboratory Technologist. A 3mL blood was obtained from each participant. After collection, blood samples were transferred into an ethylenediaminetetraacetic acid (EDTA) tube to prevent the coagulation of blood. Next, thick and thin smears were made on a well cleaned and sterilized slides. The thin smear was fixed in absolute ethanol. Subsequently, 3% stain made of Giemsa was added to the thick and thin smears for 30 minutes. The slides were later viewed under x100 objective lens of the light microscope to confirm the presence or absence of Plasmodium parasites and the species present. When about 200 microscopic fields have been observed and no parasite discovered, it is considered negative. The mean parasite density was classified according to the recommendations of Atroosh et al. . Parasite density was recorded as number of Parasite/µL of blood, assuming an average leucocyte count of 8,000/µL of blood for an average individual . The formula used is stated below
Data collected were analyzed using SPSS version 20.0. The presence or absence of malaria parasite was computed and the differences in prevalence between age groups and sex were calculated using chi square test at 95% level of confidence. The malaria parasite density was computed using the student’s t-test for dichotomous variable while ANOVA was used to determine categorical variables. Malaria-associated risk factor were determined by Bivariate logistic model. P-values of ≤0.05 were recognized as significant.
The protocol for this study was approved by Ondo State Ministry of Health (protocol number OSHREC/09/04/2018/046) the Ethical Review Committee, Federal University of Technology, Akure, Nigeria. Informed consent that were written were obtained from each adult subject. However, for children, their caregiver or guardians provided the informed consent.