Determination of diagnostic cycle threshold cutoffs for qPCR-based prevalence surveys of soil-transmitted helminth infections.
Malathi Manuel, Nils Pilotte, Joseph W S Timothy et al.
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In 30 seconds
This analysis of pre-intervention, population-based surveys within the DeWorm3 community-based cluster-randomized trial used high-throughput qPCR results from 29,980 samples to define cycle-threshold cutoffs for transmissible soil-transmitted helminth infections. A finite mixture model identified cutoffs of 34.4398 for Necator americanus and 28.57587 for Ascaris lumbricoides. For hookworms, qPCR sensitivity was 96.7%, compared with 73.2% for Kato-Katz. The study also found that qPCR Ct values distinguished moderate- to heavy-intensity hookworm infections from light-intensity infections and Kato-Katz-negative samples.
Key findings
- The model-derived Ct cutoffs were 34.4398 for N. americanus and 28.57587 for A. lumbricoides.
- For hookworm detection, qPCR sensitivity was 96.7%, compared with 73.2% for Kato-Katz.
- Moderate- to heavy-intensity hookworm infections had a median Ct of 19.1 (IQR, 17.9-19.8), versus 25.3 (IQR, 22.5-27.9) for light-intensity infections and Kato-Katz-negative samples.
Why it matters
A qPCR-positive result may reflect transmissible infection or non-infectious parasite material, so interpreting Ct values is important when estimating prevalence relevant to public health. These data-driven cutoffs offer a way to distinguish those signals and classify infection intensity in large-scale surveys, potentially improving how deworming programmes are evaluated.
What to keep in mind
Experimental spiking approaches were hindered by inefficient fecal DNA extraction. The reported bimodal distributions and derived cutoffs applied to two of the four species tested.