Temporal Changes in Ebola Transmission in Sierra Leone and Implications for Control Requirements: a Real-time Modelling Study.
BACKGROUND
Between August and November 2014, the incidence of Ebola virus disease (EVD) rose dramatically in several districts of Sierra Leone. As a result, the number of cases exceeded the capacity of Ebola holding and treatment centres. During December, additional beds were introduced, and incidence declined in many areas. We aimed to measure patterns of transmission in different regions, and evaluate whether bed capacity is now sufficient to meet future demand.


METHODS
We used a mathematical model of EVD infection to estimate how the extent of transmission in the nine worst affected districts of Sierra Leone changed between 10th August 2014 and 18th January 2015. Using the model, we forecast the number of cases that could occur until the end of March 2015, and compared bed requirements with expected future capacity.


RESULTS
We found that the reproduction number, R, defined as the average number of secondary cases generated by a typical infectious individual, declined between August and December in all districts. We estimated that R was near the crucial control threshold value of 1 in December. We further estimated that bed capacity has lagged behind demand between August and December for most districts, but as a consequence of the decline in transmission, control measures caught up with the epidemic in early 2015.


CONCLUSIONS
EVD incidence has exhibited substantial temporal and geographical variation in Sierra Leone, but our results suggest that the epidemic may have now peaked in Sierra Leone, and that current bed capacity appears to be sufficient to keep the epidemic under-control in most districts.
Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Anton
A
Camacho
Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Adam
A
Kucharski
Quality Assurance Team, UK-Med Ebola Response Team; IDEA, London, UK.
Yvonne
Y
Aki-Sawyerr
UK Joint Inter-Agency Task Force, International Security Advisory Team Compound, Freetown, Sierra Leone.
Mark A
MA
White
Health Protection Agency, London, UK; University of Strathclyde, Glasgow, UK.
Stefan
S
Flasche
London School of Hygiene & Tropical Medicine, London, UK; Public Health England, London, UK.
Marc
M
Baguelin
Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Timothy
T
Pollington
Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Julia R
JR
Carney
Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Rebecca
R
Glover
Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Elizabeth
E
Smout
Epicentre, Geneva, Switzerland.
Amanda
A
Tiffany
London School of Hygiene & Tropical Medicine, London, UK.
W John
WJ
Edmunds
London School of Hygiene & Tropical Medicine, London, UK.
Sebastian
S
Funk
ebola