Surveillance for malaria elimination in Swaziland: a national cross-sectional study using pooled PCR and serology

Michelle S Hsiang, Jimee Hwang, Simon Kunene, Chris Drakeley, Deepika Kandula, Joseph Novotny, Justin Parizo, Trevor Jensen, Marcus Tong, Jordan Kemere, Sabelo Dlamini, Bruno Moonen, Evelina Angov, Sheetij Dutta, Christian Ockenhouse, Grant Dorsey, Bryan Greenhouse, Michelle S Hsiang, Jimee Hwang, Simon Kunene, Chris Drakeley, Deepika Kandula, Joseph Novotny, Justin Parizo, Trevor Jensen, Marcus Tong, Jordan Kemere, Sabelo Dlamini, Bruno Moonen, Evelina Angov, Sheetij Dutta, Christian Ockenhouse, Grant Dorsey, Bryan Greenhouse

Abstract

Background: To guide malaria elimination efforts in Swaziland and other countries, accurate assessments of transmission are critical. Pooled-PCR has potential to efficiently improve sensitivity to detect infections; serology may clarify temporal and spatial trends in exposure.

Methodology/principal findings: Using a stratified two-stage cluster, cross-sectional design, subjects were recruited from the malaria endemic region of Swaziland. Blood was collected for rapid diagnostic testing (RDT), pooled PCR, and ELISA detecting antibodies to Plasmodium falciparum surface antigens. Of 4330 participants tested, three were RDT-positive yet false positives by PCR. Pooled PCR led to the identification of one P. falciparum and one P. malariae infection among RDT-negative participants. The P. falciparum-infected participant reported recent travel to Mozambique. Compared to performing individual testing on thousands of samples, PCR pooling reduced labor and consumable costs by 95.5%. Seropositivity was associated with age ≥20 years (11·7% vs 1·9%, P<0.001), recent travel to Mozambique (OR 4.4 [95% CI 1.0-19.0]) and residence in southeast Swaziland (RR 3.78, P<0.001).

Conclusions: The prevalence of malaria infection and recent exposure in Swaziland are extremely low, suggesting elimination is feasible. Future efforts should address imported malaria and target remaining foci of transmission. Pooled PCR and ELISA are valuable surveillance tools for guiding elimination efforts.

Conflict of interest statement

Competing Interests: The authors have read the journal's policy and have the following conflicts: MSH works at and JH is on secondment to the Global Health Group of the University of California San Francisco, which exists in part to support countries that are embarked on an evidence-based pathway towards elimination. SK is the program manager for and SD a program officer for the Swaziland National Malaria Control Program. DK, JN, and BM work with the Clinton Health Access Initiative, which is supporting malaria elimination activities in Swaziland. Other authors report no potential conflicts of interest. This does not alter the authors' adherence to all the PLoS ONE policies on sharing data and materials.

Figures

Figure 1. Participant recruitment and results for…
Figure 1. Participant recruitment and results for testing by RDT and pooled-PCR.
DBS, dried blood spots.
Figure 2. Map of Swaziland with RDT…
Figure 2. Map of Swaziland with RDT or PCR-positive participants and potential hot spots identified in serologic cluster analysis.
Figure 3. Seroprevalence to P. falciparum antigens…
Figure 3. Seroprevalence to P. falciparum antigens MSP-142 and AMA-1 by age category with 95% confidence interval half-widths.

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