Malaria Burden through Routine Reporting: Relationship between Incidence and Test Positivity Rates

Simon P. Kigozi Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom;
Infectious Diseases Research Collaboration, Kampala, Uganda;

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Ruth N. Kigozi United States Agency for International Development’s Malaria Action Program for Districts, Kampala, Uganda;

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Asadu Sserwanga Infectious Diseases Research Collaboration, Kampala, Uganda;

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Joaniter I. Nankabirwa Infectious Diseases Research Collaboration, Kampala, Uganda;
School of Medicine, Makerere University College of Health Sciences, Mulago Hospital Complex, Kampala, Uganda;

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Sarah G. Staedke Infectious Diseases Research Collaboration, Kampala, Uganda;
Department of Clinical Research, London School of Hygiene & Tropical Medicine, London, United Kingdom

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Moses R. Kamya Infectious Diseases Research Collaboration, Kampala, Uganda;
School of Medicine, Makerere University College of Health Sciences, Mulago Hospital Complex, Kampala, Uganda;

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Rachel L. Pullan Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom;

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Test positivity rate (TPR)—confirmed cases per 100 suspected cases tested, and test-confirmed malaria case rate (IR)—cases per 1,000 population, are common indicators used routinely for malaria surveillance. However, few studies have explored relationships between these indicators over time and space. We studied the relationship between these indicators in children aged < 11 years presenting with suspected malaria to the outpatient departments of level IV health centers in Nagongera, Kihihi, and Walukuba in Uganda from October 2011 to June 2016. We evaluated trends in indicators over time and space, and explored associations using multivariable regression models. Overall, 65,710 participants visited the three clinics. Pairwise comparisons of TPR and IR by month showed similar trends, particularly for TPRs < 50% and during low-transmission seasons, but by village, the relationship was complex. Village mean annual TPRs remained constant, whereas IRs drastically declined with increasing distance from the health center. Villages that were furthest away from the health centers (fourth quartile for distance) had significantly lower IRs than nearby villages (first quartile), with an incidence rate ratio of 0.40 in Nagongera (95% CI: 0.23–0.63; P = 0.001), 0.55 in Kihihi (0.40–0.75; P < 0.001), and 0.25 in Walukuba (0.12–0.51; P < 0.001). Regression analysis results emphasized a nonlinear (cubic) relationship between TPR and IR, after accounting for month, village, season, and demographic factors. Results show that the two indicators are highly relevant for monitoring malaria burden. However, interpretation differs with TPR primarily indicating demand for malaria treatment resources and IR indicating malaria risk among health facility catchment populations.

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Author Notes

Address correspondence to Simon P. Kigozi, London School of Hygiene & Tropical Medicine, Keppel St., London WC1E 7HT, United Kingdom. E-mail: skigozi@yahoo.com

Financial support: We acknowledge, with gratitude, funding from the President’s Malaria Initiative, U.S. Agency for International Development under the terms of Interagency Agreement (1U51CK000117) with the CDC for the parent study and the Fogarty International Centers training grant (D43TW7375) for this substudy.

Availability of data and materials: The dataset used and/or analyzed during the present study are available from the corresponding author on reasonable request.

Authors’ addresses: Simon P. Kigozi and Rachel L. Pullan, Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom, E-mails: skigozi@yahoo.com and rachel.pullan@lshtm.ac.uk. Ruth N. Kigozi, USAID’s Malaria Action Program for Districts, Kampala, Uganda, E-mail: kigoziruth@gmail.com. Asadu Sserwanga, Infectious Diseases Research Collaboration, Kampala, Uganda, E-mail: asserwanga@idrc-uganda.org. Joaniter I. Nankabirwa and Moses R. Kamya, School of Medicine, Makerere University College of Health Sciences, Mulago Hospital Complex, Kampala, Uganda, E-mails: jnankabirwa@yahoo.co.uk and mkamya@infocom.co.ug. Sarah G. Staedke, Department of Clinical Research, London School of Hygiene & Tropical Medicine, London, United Kingdom, E-mail: sarah.staedke@lshtm.ac.uk.

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