Reported deaths from Ebola peaked in Liberia in the week ending 2 September, falling to 35 per day during 12-18 October (see WHO Situation Reports for 15 and 25 October). As early as 9 October, National Public Radio in the US noted that reported Ebola cases in Liberia had fallen by “about 160 cases each week” from end-September. According to a 23 October news report, “Virtually everyone in Liberia agrees on a new, stunning fact: Ebola cases in Liberia are dropping.”
Why has the outbreak apparently peaked and fallen back in Liberia, while the outbreak in Sierra Leone has stampeded ahead for at least another month? The answer to that question is relevant to ongoing and anticipated well-funded public health interventions aimed at the outbreak.
Gene studies suggest Ebola has been around for at least 1,200 years and possibly much, much longer. Presumably thousands of Africans over the centuries have gotten Ebola from the wild, eg, by getting blood into cuts while butchering infected chimpanzees. The absence of recognized outbreaks before 1976 is strong evidence transmission during home-based care and funerals is not enough to sustain, much less amplify, outbreaks. Before 1976, people that were somehow infected with Ebola on average infected less than one other person.
Similarly, in well-documented Ebola outbreaks beginning in 1976, transmission within the household and during funerals has not been enough to sustain outbreaks. Amplification of infections in health care settings – transmission from patients to care-givers and to other patients – has multiplied otherwise rare infections to the point that outbreaks are recognized.
Once recognized, most of the more than 20 outbreaks to date ended within 1-3 months.
Only one continued beyond 4 months – an outbreak, in Gabon in 2001-2, continued 5 months and 5 days. The common pattern of interventions ending outbreaks to date has been to somehow stop health facilities from amplifying infections – to prevent Ebola transmission to health care workers and other patients.
A mission hospital near the Ebola River in Zaire amplified the eponymous Ebola outbreak in 1976. Injections with reused and unsterile syringes and needles infected at least 85 of the 280 who died and – through secondary infections among contacts – were directly or indirectly responsible for most deaths. The hospital closed after Ebola sickened or killed most of its staff. Although this was a sorry way to stop the hospital from further amplifying the outbreak, it was effective. After the hospital closed, the outbreak ended with home-based care before an international health aid team even began to search for cases.
During the ongoing West Africa outbreak, the health aid community has acknowledged that hospitals are dangerous places for health care workers. WHO’s Situation Report for 22 October reports 440 cases and 244 deaths among health care workers in West Africa and Nigeria through 19 October. The health aid community has commendably committed hundreds of millions of dollars in equipment and training to stop transmissions to health care staff.
However, to stop hospitals from amplifying infections, patients and not only health care workers must be protected – eg, instruments must be sterilized and gloves changed between patients. If anything is being done along these lines, there is no news. The health aid community has said next to nothing about transmissions to patients in Guinea, Liberia, and Sierra Leone – has any account been made but not reported? – and Ebola prevention messages for the general public have been silent about patients’ risks. Better reporting from Nigeria very clearly shows hospital amplification to health staff and patients: An index case flying in from Liberia started a mini-outbreak that infected 19 Nigerians – 16 acquired Ebola during health care (12 health staff and 4 patients) and 3 of these 16 infected one relative each.
Even if public health authorities are silent about patients’ risks to get Ebola during health care, people will learn of such infections through friends and rumors. When people avoid health facilities because they fear to get Ebola, or don’t want to be cremated or buried in unmarked graves, this reduces amplification of infections in health facilities. When doctors and nurses stay home or refuse to treat patients out of fear, this also protects patients. Some anecdotal reports suggest that such behaviors have been common in Liberia.
Previous Ebola outbreaks warn that health care in hospitals, not home-based care, is the biggest risk to sustain and amplify outbreaks. How much has public avoidance of health care facilities contributed to reducing Ebola transmission in Liberia? Conversely, how much did public health efforts to bring suspected and confirmed cases into hospitals beginning in March contribute to outbreak amplification in Liberia through August?
Maybe the current outbreak in West Africa is different – maybe patients cared for at home are responsible for outbreak amplification, while hospitals have been dampening the outbreak. Maybe. On the other hand, if transmission during this outbreak is similar to previous outbreaks, the massive funds provided to stem the epidemic present a promise and a threat. If patients are protected, aid-financed expansion of health facilities could save lives. On the other hand, if patients are not protected, bringing more suspected and confirmed cases into hospitals could impede rather than speed the end of the outbreak.
5. Chippaux, Outbreaks of Ebola virus disease in Africa…, available at: http://www.jvat.org/content/20/1/44
6. Taylor et al, Evidence that ebolaviruses…Miocene, available at: https://peerj.com/articles/556.pdf
7. International Commission, Ebola haemorrhagic fever in Zaire, 1976, available at: http://whqlibdoc.who.int/bulletin/1978/Vol56-No2/bulletin_1978_56%282%29_271-293.pdf
8. Fasina et al, Transmission dynamics…Nigeria, available at: http://www.eurosurveillance.org/images/dynamic/EE/V19N40/art20920.pdf