Estimating malaria attributable fraction using quantitative PCR in a longitudinal cohort in Eastern Uganda

Area of Science:

• Infectious Diseases
• Epidemiology
• Malariology

Background:

• Asymptomatic Plasmodium infections are prevalent in high-transmission areas due to acquired immunity.
• Individuals with asymptomatic infections may be misdiagnosed with clinical malaria when seeking care for non-malarial fevers.

Purpose of the Study:

• To estimate the malaria attributable fraction (MAF) of fevers in a Ugandan cohort using qPCR parasite densities.
• To assess how MAF varies across different age groups and geographical zones.
• To compare MAF-corrected malaria incidence with standard clinical malaria definitions.

Main Methods:

• A cohort of 659 individuals in eastern Uganda was followed for up to 3 years.
• Quantitative PCR (qPCR) was used to determine Plasmodium parasite densities.
• Distributions of qPCR parasite densities were analyzed to estimate the MAF for febrile episodes.

Main Results:

• Overall MAF ranged from 54-64% across three zones, with prevalence of P. falciparum by qPCR between 47-63%.
• MAF was highest in children under five (72%) and lowest in adults over 16 (45%).
• MAF-corrected incidence was significantly higher than standard clinical malaria definitions, particularly in adults (70% higher).

Conclusions:

• Standard parasite density thresholds used to define clinical malaria underestimate true incidence.
• Estimating MAF is crucial for accurate malaria burden assessment and intervention studies.
• Intervention studies should consider incorporating MAF estimation into their design for precise incidence effect measurement.