Temporal and Spatial Differences between Symptomatic and Asymptomatic Malaria Infections in the Chittagong Hill Districts, Bangladesh

Kerry L. ShannonDepartment of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
Department of Emergency Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland;

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Timothy ShieldsDepartment of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;

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Sabeena AhmedInfectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Hafizur RahmanLaboratory Sciences and Services Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Chai Shwai PrueInfectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Jacob KhyangInfectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Malathi RamDepartment of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;

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M. Zahirul HaqHealth Systems and Population Studies Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Jasmin AkterInfectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Mohammad Shafiul AlamInfectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Gregory E. GlassDepartment of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;

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Myaing M. NyuntDepartment of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;
Health Systems and Population Studies Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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David A. SackDepartment of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;

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David J. Sullivan Jr.Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;

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Wasif A. KhanInfectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh;

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Frank C. CurrieroDepartment of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland;

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Mapping asymptomatic malaria infections, which contribute to the transmission reservoir, is important for elimination programs. This analysis compared the spatiotemporal patterns of symptomatic and asymptomatic Plasmodium falciparum malaria infections in a cohort study of ∼25,000 people living in a rural hypoendemic area of about 179 km2 in a small area of the Chittagong Hill Districts of Bangladesh. Asymptomatic infections were identified by active surveillance; symptomatic clinical cases presented for care. Infections were identified by a positive rapid diagnostic test and/or microscopy. Fifty-three subjects with asymptomatic P. falciparum infection were compared with 572 patients with symptomatic P. falciparum between mid-October 2009 and mid-October 2012 with regard to seasonality, household location, and extent of spatial clustering. We found increased spatial clustering of symptomatic compared with asymptomatic infections, and the areas of high intensity were only sometimes overlapping. Symptomatic cases had a distinct seasonality, unlike asymptomatic infections, which were detected year-round. In a comparison of 42 symptomatic Plasmodium vivax and 777 symptomatic P. falciparum cases from mid-October 2009 through mid-March 2015, we found substantial spatial overlap in areas with high infection rates, but the areas with the greatest concentration of infection differed. Detection of both symptomatic P. falciparum and symptomatic P. vivax infections was greater during the May-to-October high season, although a greater proportion of P. falciparum cases occurred during the high season compared with P. vivax. These findings reinforce that passive malaria surveillance and treatment of symptomatic cases will not eliminate the asymptomatic reservoirs that occur distinctly in time and space.

Author Notes

Address correspondence to Kerry L. Shannon, XXXXX. E-mail: kshanno5@jhmi.edu.

Financial support: This study was funded by the Johns Hopkins Malaria Research Institute at the Johns Hopkins Bloomberg School of Public Health (grant no. 00679) and the Johns Hopkins MSTP program and Johns Hopkins Department of International Health for funding of K. S. The International Center for Diarrheal Disease Research, Bangladesh, is also grateful to the governments of Bangladesh, Canada, Sweden, and the United Kingdom for providing core/unrestricted support. We are also indebted to the Johns Hopkins Center for Global Health and John Snow, Inc., who provided travel funding for a student investigator.

Authors’ addresses: Kerry L. Shannon, Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, and Department of Emergency Medicine, Johns Hopkins School of Medicine, Baltimore, MD, E-mail: kshanno5@jhmi.edu. Timothy Shields and Gregory E. Glass, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, and Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, E-mails: tshield2@jhu.edu and gglass@ufl.edu. Sabeena Ahmed, Chai Shwai Prue, Jacob Khyang, Jasmin Akter, Mohammad Shafiul Alam, and Wasif A. Khan, Infectious Diseases Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh, E-mails: sabeena@icddrb.org, dr_prue@yahoo.com, khyang555@gmail.com, ajasmin@icddrb.org, shafiul@icddrb.org, and wakhan@icddrb.org. Hafizur Rahman, Laboratory Sciences and Services Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh, E-mail: hafizur@icddrb.org. Malathi Ram and David A. Sack, Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, E-mails: mram1@jh.edu and dsack1@jhu.edu. M. Zahirul Haq, Health Systems and Population Studies Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh, E-mail: mzhaq@icddrb.org. Myaing M. Nyunt, Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, and Health Systems and Population Studies Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh, E-mail: myaingnyunt@gmail.com. David J. Sullivan Jr., Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, E-mail: dsulliv7@jhmi.edu. Frank C. Curriero, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, E-mail: fcurriero@jhu.edu.

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