Estimation of malaria transmission intensity in southern Ghana using rapid diagnostic test derived sero-prevalence rates

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An understanding of the epidemiology of malaria in an area is critical for the design and evaluation of control efforts. The Dangme West district has three distinct ecological zones, a forest (Dodowa sub district), a coastal zone (Prampram sub district) and a lakeside zone (Osudoku sub district). The current data for the Dangme West District of Ghana dates back to 1993, when the parasite prevalence ranged from 42% (dry season) to 51% (rainy season), while in Prampram the prevalence were 20% and 37% respectively. The annual Entomological Inoculation Rate (EIR) was 22 and 3.6 infective bites per person per year in Dodowa and Prampram respectively in 1993. Though many malaria interventions have been rolled out through research and program activities, there were no current data to ascertain the veracity of interventions and guide further program actions. The objective of this study was therefore to update and determine the complete the epidemiology of malaria in Dangme West district. The study was in 3 parts; Prevalence: 2 cross-sectional surveys (6854 persons of both genders and all ages, selected using multistage cluster sampling) were conducted at the end of the wet (August 2011) and dry (March 2012) seasons. Participants were interviewed using questionnaires after which finger prick blood samples were taken for Rapid Diagnostic Tests (RDTs) and blood films to check for malaria. Incidence: A cohort of 3156 participants of all ages, from the 3 zones was selected using multistage cluster sampling. Participants were followed once a month for a year. A history of fever within the past 2 weeks was elicited at each visit. Those who responded positively had finger prick blood samples taken for RDT and blood films. Entomology: 4 houses per zone were randomly selected for mosquito collection per month for a year using Human Landing catches. Ethical approval was obtained from Kwame Nkrumah University of Science and Technology Committee on Human Research, Publications and Ethics: CHRPE 189/10 and Ghana Health Service: GHS-ER: 03/5/11. Data were double entered in EPIDATA, cleaned and analyzed in STATA 12. There was minimal seasonality in blood slide positivity in the dry and wet seasons, with an average parasite prevalence of 6.5%, (Lakeside 2.7% to 8.5% Coastal). The dominant parasite specie was Plasmodium falciparum (96%). The age-specific parasite prevalence was 9% in 0-9 year olds, 8% in 10-19 year olds, 5% in 20-29 year olds, 3% in 30-39 years and 4% in those aged 40 years and above. The corresponding age-specific MSP-119 prevalence was 37%, 58%, and 60%, 66% and 67% respectively. 8% of participants in the incidence study reported a history of fever in the last 48 hours, 3% used antimalarial for perceived fever and 6% had used an ITN the night before home visits. The Forest zone had an incidence rate of 85/1000py (slide), Coastal 41/1000py and Lakeside 13/1000py. The absence of a ceiling in a room was associated with an excess risk of 15%. The incidence rate was 119/1000py in 0-4 year olds, 136/1000py in 5-9 year, 50/1000py in 10-19 year, 9/1000py in 20-29 year, 18/1000/py in 30- 39 year olds and 24/1000py in those over 40 years. The district EIR was 81 infective bites per person year (ppy). April had the highest EIR of 1/pp/night. The Lakeside zone had an EIR of 100/ppy; Forest 81 ppy and Coastal 30ppy for the same period. The main vector species was An. gambiae s.l, which constituted 95%, with An. funestus Giles forming the rest. Overall rates had decreased by about 40% from the 1993 levels. The Lakeside zone had the lowest malaria incidence despite vast irrigated fields. The Forest zone, with the lowest verified ITN use, and the 5-9 year age group bore the brunt of morbidity. There is reduction in malaria burden in the area in the last 20 years, with more marked reduction in the Lakeside than at the Coastal and Forest. The Lakeside with the highest ITN use had the lowest parasite prevalence and incidence rates. ITN distribution and use need to be improved in the Forest and Coastal zones and access to testing and treatment with quality assured ACTs improved in the Osudoku zone. Research into effective combination of interventions to target the 5-9 and 10-19 year groups need to be done to address disease burden and asymptomatic carriage in those age groups.
A thesis submitted to the Department of Epidemiology and Biostatistics, College of Health Sciences, School of Public Health, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Public Health,