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Malar J. 2018 Dec 19;17(1):480. doi: 10.1186/s12936-018-2626-5.

Subpatent malaria in a low transmission African setting: a cross-sectional study using rapid diagnostic testing (RDT) and loop-mediated isothermal amplification (LAMP) from Zambezi region, Namibia.

Author information

1
Malaria Elimination Initiative, Global Health Group, University of California, San Francisco (UCSF), San Francisco, CA, USA.
2
Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
3
Multidisciplinary Research Center, University of Namibia, Windhoek, Namibia.
4
Burnet Institute for Medical Research and Public Health, Melbourne, Australia.
5
Division of HIV, Infectious Diseases and Global Medicine, Department of Medicine, UCSF, San Francisco, CA, USA.
6
Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
7
Wits Research Institute for Malaria, University of Witwatersrands, Johannesburg, South Africa.
8
National Vectorborne Disease Control Programme, Namibia Ministry of Health and Social Services, Windhoek, Namibia.
9
Malaria Elimination Initiative, Global Health Group, University of California, San Francisco (UCSF), San Francisco, CA, USA. michelle.hsiang@utsouthwestern.edu.
10
Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX, USA. michelle.hsiang@utsouthwestern.edu.
11
Department of Pediatrics, UCSF Benioff Children's Hospital, San Francisco, CA, USA. michelle.hsiang@utsouthwestern.edu.

Abstract

BACKGROUND:

Subpatent malaria infections, or low-density infections below the detection threshold of microscopy or standard rapid diagnostic testing (RDT), can perpetuate persistent transmission and, therefore, may be a barrier for countries like Namibia that are pursuing malaria elimination. This potential burden in Namibia has not been well characterized.

METHODS:

Using a two-stage cluster sampling, cross-sectional design, subjects of all age were enrolled during the end of the 2015 malaria transmission season in Zambezi region, located in northeast Namibia. Malaria RDTs were performed with subsequent gold standard testing by loop-mediated isothermal amplification (LAMP) using dried blood spots. Infection prevalence was measured and the diagnostic accuracy of RDT calculated. Relationships between recent fever, demographics, epidemiological factors, and infection were assessed.

RESULTS:

Prevalence of Plasmodium falciparum malaria infection was low: 0.8% (16/1919) by RDT and 2.2% (43/1919) by LAMP. All but one LAMP-positive infection was RDT-negative. Using LAMP as gold standard, the sensitivity and specificity of RDT were 2.3% and 99.2%, respectively. Compared to LAMP-negative infections, a higher portion LAMP-positive infections were associated with fever (45.2% vs. 30.4%, p = 0.04), though 55% of infections were not associated with fever. Agricultural occupations and cattle herding were significantly associated with LAMP-detectable infection (Adjusted ORs 5.02, 95% CI 1.77-14.23, and 11.82, 95% CI 1.06-131.81, respectively), while gender, travel, bed net use, and indoor residual spray coverage were not.

CONCLUSIONS:

This study presents results from the first large-scale malaria cross-sectional survey from Namibia using molecular testing to characterize subpatent infections. Findings suggest that fever history and standard RDTs are not useful to address this burden. Achievement of malaria elimination may require active case detection using more sensitive point-of-care diagnostics or presumptive treatment and targeted to high-risk groups.

KEYWORDS:

Asymptomatic; LAMP; Malaria; Malaria elimination; Namibia; RDT; Rapid diagnostic test; Subclinical; Submicroscopic; Subpatent

PMID:
30567537
PMCID:
PMC6299963
DOI:
10.1186/s12936-018-2626-5
[Indexed for MEDLINE]
Free PMC Article

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