Evaluation of the benefits and risks of introducing Ebola community care centers, Sierra Leone

Abstract

In some parts of western Africa, Ebola treatment centers (ETCs) have reached capacity. Unless capacity is rapidly scaled up, the chance to avoid a generalized Ebola epidemic will soon diminish. The World Health Organization and partners are considering additional Ebola patient care options, including community care centers (CCCs), small, lightly staffed units that could be used to isolate patients outside the home and get them into care sooner than otherwise possible. Using a transmission model, we evaluated the benefits and risks of introducing CCCs into Sierra Leone's Western Area, where most ETCs are at capacity. We found that use of CCCs could lead to a decline in cases, even if virus transmission occurs between CCC patients and the community. However, to prevent CCC amplification of the epidemic, the risk of Ebola virus-negative persons being exposed to virus within CCCs would have to be offset by a reduction in community transmission resulting from CCC use.

Figure 1

Structure of transmission model used to evaluate the benefits and risks of introducing CCCs into Western Area, Sierra Leone. Persons start off being susceptible to infection (S). Upon infection with Ebola virus, they enter an incubation period (E), and at symptom onset, they become infectious in the community (I₊). After this point, infected persons seek health care in CCCs or ETCs; if centers are full, the infectious persons remain in the community until the infection is resolved (R) (i.e., the patients have recovered from the disease or are dead and buried). Patients admitted to ETCs and CCCs also move into the resolved compartment (R). We also assume that Ebola virus–susceptible persons could also become infected with other febrile diseases that have Ebola virus disease–like symptoms (I_–). These Ebola virus–negative patients also seek health care; if centers are full, the patients return to the susceptible compartment (S) as symptoms wane. We assume the latent period is 9.4 days, the average time from symptom onset to CCC attendance is 3 days, and the average interval from symptom onset to ETC attendance is 4.6 days. CCCs, Ebola community care centers; ETCs, Ebola treatment centers.

Figure 2

Model fits and forecasts used to evaluate the benefits and risks of introducing Ebola community care centers into Western Area, Sierra Leone. A) Reported cases over time. Black points show reported incidence data. B) No. patients in ETC beds. Blue lines to the left of the dashed vertical divides show the median estimate; blues line to the right of the dashed vertical divides show forecast with no change in number of ETC beds; green lines show forecast if 500 ETC beds are introduced on December 15, 2014. Shaded areas represent 95% credible interval, which reflects uncertainty about reporting and model parameters; darker shading indicates overlap between 2 forecasts. Estimates were scaled depending on the number of daily situation reports issued by the Sierra Leone Ministry of Health and Sanitation each week (see https://drive.google.com/file/d/0B_BzCqSK1DZaYnRoeWtHOTU2TVk/). ETC, Ebola treatment center.

Figure 3

Factors influencing reduction or amplification of Ebola virus infection in the community if 500 CCC beds were introduced in Western Area, Sierra Leone, on December 15, 2014. A) Change in infection compared with baseline scenario (259 Ebola treatment center beds) between December 1, 2014, and February 1, 2015, for a range of values for reduction in transmission and probability of exposure to virus. Median parameter estimates for Western Area were used (Table). B) Change in infection over time. Black line, baseline scenario. Blue line, 500 CCC beds with transmission reduced by 75% (blue line in A), and Ebola virus–negative patients have 25% probability of exposure to virus. Red line, 500 CCC beds with transmission reduced by 25% (red line in A), and Ebola virus–negative patients have 50% probability of exposure to virus. Shaded areas show 95% bootstrapped credible intervals generated from 1,000 simulations with parameters sampled from posterior estimates. We assumed that time from symptom onset to CCC attendance was 3 days and that 50% of symptomatic patients were Ebola virus–positive. CCC, Ebola community care center.

Figure 4

Estimated number of CCC beds required to control Ebola virus epidemic in Western Area, Sierra Leone. A) Number of CCC beds required to turn over the outbreak (i.e., reduce the reproduction number, R, to <1). When transmission is reduced by only 50%, no amount of CCC beds can stop the growth in cases. We assume there is a 10% probability that Ebola virus–negative patients are exposed to virus. Lines show bootstrapped 95% credible intervals generated from 1,000 simulations with parameters sampled from posterior estimates; points show median estimates. B) Number of CCC beds required to turn over the epidemic when an additional 500 Ebola treatment center beds are also introduced on December 15, 2014. CCC, Ebola community care center.