title: Transmission dynamics of Ebola virus disease and intervention effectiveness in Sierra Leone.
abstract: Sierra Leone is the most severely affected country by an unprecedented outbreak of Ebola virus disease (EVD) in West Africa. Although successfully contained, the transmission dynamics of EVD and the impact of interventions in the country remain unclear. We established a database of confirmed and suspected EVD cases from May 2014 to September 2015 in Sierra Leone and mapped the spatiotemporal distribution of cases at the chiefdom level. A Poisson transmission model revealed that the transmissibility at the chiefdom level, estimated as the average number of secondary infections caused by a patient per week, was reduced by 43% [95% confidence interval (CI): 30%, 52%] after October 2014, when the strategic plan of the United Nations Mission for Emergency Ebola Response was initiated, and by 65% (95% CI: 57%, 71%) after the end of December 2014, when 100% case isolation and safe burials were essentially achieved, both compared with before October 2014. Population density, proximity to Ebola treatment centers, cropland coverage, and atmospheric temperature were associated with EVD transmission. The household secondary attack rate (SAR) was estimated to be 0.059 (95% CI: 0.050, 0.070) for the overall outbreak. The household SAR was reduced by 82%, from 0.093 to 0.017, after the nationwide campaign to achieve 100% case isolation and safe burials had been conducted. This study provides a complete overview of the transmission dynamics of the 2014-2015 EVD outbreak in Sierra Leone at both chiefdom and household levels. The interventions implemented in Sierra Leone seem effective in containing the epidemic, particularly in interrupting household transmission.
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Fang
authors.affiliation: Department of Biostatistics, University of Florida, Gainesville, FL 32610; Emerging Pathogens Institute, University of Florida, Gainesville, FL 32610;
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Jia-Fu
authors.initials: JF
authors.lastname: Jiang
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Hong-Wu
authors.initials: HW
authors.lastname: Yao
authors.affiliation: The Sierra Leone Ministry of Health and Sanitation, Freetown, Sierra Leone;
authors.forename: David
authors.initials: D
authors.lastname: Kargbo
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Xin-Lou
authors.initials: XL
authors.lastname: Li
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Bao-Gui
authors.initials: BG
authors.lastname: Jiang
authors.affiliation: The Sierra Leone Ministry of Health and Sanitation, Freetown, Sierra Leone;
authors.forename: Brima
authors.initials: B
authors.lastname: Kargbo
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Yi-Gang
authors.initials: YG
authors.lastname: Tong
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Ya-Wei
authors.initials: YW
authors.lastname: Wang
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Kun
authors.initials: K
authors.lastname: Liu
authors.affiliation: The Sierra Leone Ministry of Health and Sanitation, Freetown, Sierra Leone;
authors.forename: Abdul
authors.initials: A
authors.lastname: Kamara
authors.affiliation: The Sierra Leone Ministry of Health and Sanitation, Freetown, Sierra Leone;
authors.forename: Foday
authors.initials: F
authors.lastname: Dafae
authors.affiliation: Sierra Leone-China Friendship Hospital, Freetown, Sierra Leone;
authors.forename: Alex
authors.initials: A
authors.lastname: Kanu
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Rui-Ruo
authors.initials: RR
authors.lastname: Jiang
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Ye
authors.initials: Y
authors.lastname: Sun
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China; Anhui Medical University, Hefei 230032, People's Republic of China;
authors.forename: Ruo-Xi
authors.initials: RX
authors.lastname: Sun
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Wan-Jun
authors.initials: WJ
authors.lastname: Chen
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China;
authors.forename: Mai-Juan
authors.initials: MJ
authors.lastname: Ma
authors.affiliation: Department of Biostatistics, University of Florida, Gainesville, FL 32610; Emerging Pathogens Institute, University of Florida, Gainesville, FL 32610;
authors.forename: Natalie E
authors.initials: NE
authors.lastname: Dean
authors.affiliation: The Sierra Leone Ministry of Health and Sanitation, Freetown, Sierra Leone;
authors.forename: Harold
authors.initials: H
authors.lastname: Thomas
authors.affiliation: Department of Biostatistics, University of Florida, Gainesville, FL 32610; Emerging Pathogens Institute, University of Florida, Gainesville, FL 32610;
authors.forename: Ira M
authors.initials: IM
authors.lastname: Longini
authors.affiliation: Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109 caowc@bmi.ac.cn betz@fhcrc.org.
authors.forename: M Elizabeth
authors.initials: ME
authors.lastname: Halloran
authors.affiliation: The State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China; caowc@bmi.ac.cn betz@fhcrc.org.
authors.forename: Wu-Chun
authors.initials: WC
authors.lastname: Cao
mesh_terms: D016208:Databases, Factual; D029043:Ebolavirus; D005260:Female; D019142:Hemorrhagic Fever, Ebola / Q000453:epidemiology* / Q000628:therapy* / Q000635:transmission*; D006801:Humans; D008297:Male; D008954:Models, Biological; D012807:Sierra Leone / Q000453:epidemiology
keywords: Ebola virus disease; household transmission; intervention effectiveness; secondary attack rate; spatiotemporal modeling