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Published Online October 30 2014
Science DOI: 10.1126/science.1260612
EBOLA EPIDEMIOLOGY
Strategies for containing Ebola in West Africa
Abhishek Pandey1,*, Katherine E. Atkins1,*, Jan Medlock2, Natasha Wenzel1, Jeffrey P. Townsend3, James E. Childs4, Tolbert G. Nyenswah5, Martial L. Ndeffo-Mbah1, Alison P. Galvani1,4,?
+ Author Affiliations
ABSTRACT
The ongoing Ebola outbreak poses an alarming risk to the countries of West Africa and beyond. To assess the effectiveness of containment strategies, we developed a stochastic model of Ebola transmission between and within the general community, hospitals, and funerals, calibrated to incidence data from Liberia. We find that a combined approach of case isolation, contact tracing with quarantine and sanitary funeral practices must be implemented with utmost urgency in order to reverse the growth of the outbreak. Under status quo intervention, our projections indicate that the Ebola outbreak will continue to spread, generating a predicted 224 (95% CI: 134 ? 358) cases daily in Liberia alone by December, highlighting the need for swift application of multifaceted control interventions.
A multinational Ebola outbreak of unprecedented magnitude was declared a Public Health Emergency of International Concern by the World Health Organization (WHO) on August 8, 2014 (1). From Guinea, the outbreak has spread to the neighboring nations of Liberia and Sierra Leone, subsequently expanding into Nigeria and Senegal (2). Imported Ebola cases have recently led to transmission in the US and Spain (2). As of 15 October, over 9,000 cases and 4,000 fatalities have been reported, with the majority of both occurring in Liberia (2).
Initial Ebola symptoms include fever, malaise, myalgia, and headache, followed by pharyngitis, vomiting, diarrhea and maculopapular rash (3). Severe and fatal stages are accompanied by hemorrhagic diathesis and multi-organ dysfunction (3). Human-to-human transmission occurs primarily via contact with body fluids (3). Inadequate and improper use of personal protective equipment (PPE), compounded by staff shortages in isolation wards pose major risks of infection for healthcare workers (4, 5), leading to nosocomial transmission that can cripple health services (5). Ebola transmission is further exacerbated by traditional West African funeral practices that may involve washing, touching, and kissing the body (5?7). Given the current lack of licensed therapeutic treatments and vaccines (8), near-term measures to curb transmission must rely on non-pharmaceutical interventions, including quarantine, case isolation, contact precautions, and sanitary burial practices that consist of disinfecting the cadaver before inclosure in a body bag that is further disinfected.
snip
We calculated R0 for Ebola in Liberia to be 1.63 (95% CI: 1.59?1.66) prior to widespread interventions, consistent with other R0 estimates for the current outbreak (16?18), but somewhat lower than those calculated for the previous outbreaks, which ranged between 1.8 and 2.7 (19?21). Our novel model structure allowed us to partition the contribution of different transmission routes in sustaining the epidemic. We calculated that in the absence of nosocomial transmission, R0 = 1.48 (1.44?1.51); without community transmission, R0 = 1.39 (1.35?1.42); if only funeral transmission were present, and both nosocomial and community transmission were eliminated), R0 = 1.16 (1.13?1.18); and if funeral transmission were absent (but community and hospital transmission were present), R0 = 0.93 (0.87?0.99).
These results for R0 imply that reducing transmission in hospitals and the community is insufficient to stem the exponentially growing epidemic. To stem Ebola transmission in Liberia, it is imperative to simultaneously restrict traditional burials which are effectively serving as superspreader events (22, 23).
[B]snip
Under-reporting might also manifest via asymptomatic infections, which have been observed in previous outbreaks (26). While there is considerable empirical uncertainty regarding the proportion of infections that are asymptomatic, our sensitivity analysis indicates that the larger the proportion of asymptomatic infections, the greater the impact of intervention effectiveness (SOM, Fig. 4).
snip
The implementation of effective interventions needed to reverse the growth of the Ebola outbreak in impoverished West African countries will be logistically challenging even with substantial international aid, but impossible without it.
Science DOI: 10.1126/science.1260612
EBOLA EPIDEMIOLOGY
Strategies for containing Ebola in West Africa
Abhishek Pandey1,*, Katherine E. Atkins1,*, Jan Medlock2, Natasha Wenzel1, Jeffrey P. Townsend3, James E. Childs4, Tolbert G. Nyenswah5, Martial L. Ndeffo-Mbah1, Alison P. Galvani1,4,?
+ Author Affiliations
ABSTRACT
The ongoing Ebola outbreak poses an alarming risk to the countries of West Africa and beyond. To assess the effectiveness of containment strategies, we developed a stochastic model of Ebola transmission between and within the general community, hospitals, and funerals, calibrated to incidence data from Liberia. We find that a combined approach of case isolation, contact tracing with quarantine and sanitary funeral practices must be implemented with utmost urgency in order to reverse the growth of the outbreak. Under status quo intervention, our projections indicate that the Ebola outbreak will continue to spread, generating a predicted 224 (95% CI: 134 ? 358) cases daily in Liberia alone by December, highlighting the need for swift application of multifaceted control interventions.
A multinational Ebola outbreak of unprecedented magnitude was declared a Public Health Emergency of International Concern by the World Health Organization (WHO) on August 8, 2014 (1). From Guinea, the outbreak has spread to the neighboring nations of Liberia and Sierra Leone, subsequently expanding into Nigeria and Senegal (2). Imported Ebola cases have recently led to transmission in the US and Spain (2). As of 15 October, over 9,000 cases and 4,000 fatalities have been reported, with the majority of both occurring in Liberia (2).
Initial Ebola symptoms include fever, malaise, myalgia, and headache, followed by pharyngitis, vomiting, diarrhea and maculopapular rash (3). Severe and fatal stages are accompanied by hemorrhagic diathesis and multi-organ dysfunction (3). Human-to-human transmission occurs primarily via contact with body fluids (3). Inadequate and improper use of personal protective equipment (PPE), compounded by staff shortages in isolation wards pose major risks of infection for healthcare workers (4, 5), leading to nosocomial transmission that can cripple health services (5). Ebola transmission is further exacerbated by traditional West African funeral practices that may involve washing, touching, and kissing the body (5?7). Given the current lack of licensed therapeutic treatments and vaccines (8), near-term measures to curb transmission must rely on non-pharmaceutical interventions, including quarantine, case isolation, contact precautions, and sanitary burial practices that consist of disinfecting the cadaver before inclosure in a body bag that is further disinfected.
snip
We calculated R0 for Ebola in Liberia to be 1.63 (95% CI: 1.59?1.66) prior to widespread interventions, consistent with other R0 estimates for the current outbreak (16?18), but somewhat lower than those calculated for the previous outbreaks, which ranged between 1.8 and 2.7 (19?21). Our novel model structure allowed us to partition the contribution of different transmission routes in sustaining the epidemic. We calculated that in the absence of nosocomial transmission, R0 = 1.48 (1.44?1.51); without community transmission, R0 = 1.39 (1.35?1.42); if only funeral transmission were present, and both nosocomial and community transmission were eliminated), R0 = 1.16 (1.13?1.18); and if funeral transmission were absent (but community and hospital transmission were present), R0 = 0.93 (0.87?0.99).
These results for R0 imply that reducing transmission in hospitals and the community is insufficient to stem the exponentially growing epidemic. To stem Ebola transmission in Liberia, it is imperative to simultaneously restrict traditional burials which are effectively serving as superspreader events (22, 23).
[B]snip
Under-reporting might also manifest via asymptomatic infections, which have been observed in previous outbreaks (26). While there is considerable empirical uncertainty regarding the proportion of infections that are asymptomatic, our sensitivity analysis indicates that the larger the proportion of asymptomatic infections, the greater the impact of intervention effectiveness (SOM, Fig. 4).
snip
The implementation of effective interventions needed to reverse the growth of the Ebola outbreak in impoverished West African countries will be logistically challenging even with substantial international aid, but impossible without it.