BRIEF REPORT Open Forum Infectious Diseases BRIEF REPORT • OFID • 1 Sero-evaluation of Immune Responses to Vibrio cholerae in a Postelimination Setting Tai The Diep, 1 Owen Jensen, 2 Nguyen Van Thuong, 1 Nguyen Thi Ngoc Nhi, 1 Nguyen Ngoc Anh Thu, 1 Vo Ngoc Quang, 1 Truong Cong Hieu, 1 Hoang Anh Thang, 1 Nguyen Dieu Thuy, 1 Ho Vinh Thang, 1 Ho Trung Tuyen, 3 Le Dang Ngan, 4 Nguyen Thi Thanh Ha, 5 Than Duc Dung, 5 Cole P. Anderson, 2 Andrew S. Azman, 6 and Daniel T. Leung 2,7, 1 Pasteur Institute, Ho Chi Minh City, Vietnam, 2 Division of Infectious Diseases, University of Utah, Salt Lake City, Utah, USA, 3 Provincial Preventive Medical Centres, Ben Tre, Vietnam, 4 Provincial Preventive Medical Centres, Tien Giang, Vietnam, 5 City’s Children Hospital, Ho Chi Minh City, Vietnam, 6 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA, and 7 Division of Microbiology & Immunology, University of Utah, Salt Lake City, Utah, USA Cholera remains a signifcant public health problem world- wide. In settings of declining incidence, serosurveillance may be used to augment clinical surveillance. We utilized dried blood spot sampling and cholera-specifc antibody testing to examine the serologic profles of vaccinated and unvaccinated children in southern Vietnam, where cholera was recently eliminated. Keywords. antibody; cholera; dried blood spots; serosurveillance; Vietnam. Vibrio cholerae O1 is a water-borne intestinal pathogen and the causative agent of cholera, an acutely dehydrating diarrheal disease. Despite increased sanitation and access to clean water worldwide, cholera remains endemic to many areas, particu- larly in southeast Asia and Sub-Saharan Africa, causing an es- timated 3 million infections and 100   000 deaths annually [1]. In 2017, the Global Task Force on Cholera Control announced an initiative to signifcantly reduce cholera deaths and elimi- nate cholera in upwards of 20 countries by 2030. Teir strategy focuses on cholera prevention through increased access to clean water, sanitation, and hygiene promotion, targeted oral cholera vaccine (OCV) deployment, and improved early detec- tion and surveillance in endemic areas and cholera “hotspots.” To monitor progress toward these 2030 goals, large improve- ments in clinical surveillance are needed, including systematic laboratory confrmation of acute watery diarrhea cases. In many countries, this scale-up may not be feasible for years to come. Serosurveillance may provide 1 potential approach to augment clinical surveillance data in assessing changes in transmission. However, to date, we have few data on cholera-specifc serolog- ical measures in populations that have brought cholera under control. Vietnam, a country of 90 million persons, has deployed >11 million OCV doses in areas at risk for cholera since 1998, mostly targeting young children aged 2–5 years. Over this time period when OCV was deployed, together with im- provements in water and sanitation infrastructure, cholera incidence has declined, and Vietnam has not recorded a case since 2010 [2]. In the absence of sentinel cases, envi- ronmental and population sampling to identify V. cholerae O1 may be challenging, and there remains a need for im- proved cholera diagnostic capabilities, particularly in lower- resourced and remote areas. We have demonstrated the use of dried blood spot (DBS) sampling to be an inexpensive, safe, and efcient means of blood collection for testing immuno- logical responses against V. cholerae O1 [3]. Terefore, we lev- eraged this new means of testing to examine the anticholera antibody response in a population that has presumably been cholera-free for almost a decade. METHODS Ethics Statement This study protocol was reviewed and approved by the Ethical Committees of Pasteur Institute of Ho Chi Minh City, the Vietnam Ministry of Health, and the University of Utah. Written informed consent was obtained from all participants for this study. Sample Collection and Transport We collected DBS samples in July–August 2018 from a sample of children aged 4–10 years at Provincial Preventive Medical Centres (PPMCs) in Tien Giang and Ben Tre. Children with documented receipt of the OCV mORCVAX during campaigns in September 2014 (Tien Giang, 4 years before sampling) and October–November 2015 (Ben Tre, 2 years 9 months before sampling) were recruited for the study. Between November 2018 and February 2019, we also collected DBS samples from unvaccinated children aged 1 month to 8 years who were hospitalized with acute watery diarrhea at a pediatric hospital in Ho Chi Minh City, Vietnam (Figure 1A). DBS samples were collected on Whatman 903 filter paper, and all cards were stored in sealed nylon bags Received 10 January 2020; editorial decision 13 April 2020; accepted 17 April 2020. Correspondence: Daniel T. Leung, MD, MSc, 30 North 1900 East, Rm 4B319, Salt Lake City, UT 84132 (daniel.leung@utah.edu). Open Forum Infectious Diseases ® © The Author(s) 2020. Published by Oxford University Press on behalf of Infectious Diseases Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (http://creativecommons.org/licenses/ by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com DOI: 10.1093/ofd/ofaa136 Downloaded from https://academic.oup.com/ofid/article/7/5/ofaa136/5823065 by guest on 05 March 2023