The surge of Ebola virus disease (EVD) that began in December 2013 in 3 West African countries (Guinea, Liberia, and Sierra Leone) is the largest ever documented. ¹ It has once again brought into focus the confusion associated with the use of the term epidemic. Ebola, one of numerous viral hemorrhagic fevers, ² is a severe, often fatal illness in humans. ³ According to the World Health Organization (WHO) Situation Report of 17 February 2016, ⁴ 28,639 cases and 11,316 deaths were reported to the WHO up to 14 February 2016.

Given these numbers, the ongoing Ebola episode should be described as an epidemic. According to the literature, whereas an outbreak is a sudden rise in the occurrence (the number of cases) of a disease,Reference Aronson and Shope ⁵ an epidemic is the occurrence of more cases of a disease than is anticipated in a community or region during a given period by previous experience.Reference Green, Swartz and Mayshar ⁶ Nevertheless, leading health organizations, such as the WHO and the Centers for Disease Control and Prevention (CDC), continue to characterize it as an outbreak. ^{7 , 8} For example, a news release published on the WHO website as recently as September 19 dubs the current Ebola epidemic an “ongoing outbreak.” ⁸ Similarly, a CDC website headline reads, “2014 Ebola Outbreak in West Africa.” However, in his speech on September 16, 2014, at the CDC, President Barack Obama referred to Ebola as an epidemic.Reference Cooper and Fink ⁹ Although in later speeches Obama tried to placate the public regarding the crisis, behind the scenes he was concerned about the escalating episode and even criticized the CDC for its response as being “not tight,”Reference Fitzgerald ¹⁰ which suggests that his use of the term epidemic was not accidental.

Following the work of Kahneman and Tversky and others in the 1970s and early 1980s,Reference Kahneman and Tversky ^{11 -} Reference Tversky and Kahneman ¹³ studies have shown that that the public’s response to a given message can depend on how the message is tailored and how it is subsequently encoded by the recipient.Reference Davis ^{14 ,} Reference Pelletier and Sharp ¹⁵ When health authorities make a decision—to declare or not to declare an epidemic or an outbreak, for example—this decision frames the risk to the public and has political, economic, and policy implications, as well as implications for public health and for the public’s trust.

The authorities’ deliberation regarding whether to frame a disease as an epidemic or a pandemic may also arise from conflicts among experts, who continue to deliberate as to when to employ different terms in light of the emphases accompanying them (Kimball et al., written communication, September 2014). When a strange type of illness occurs, or an unusually large number of people develop an illness or symptoms, the situation may be considered an outbreak, an epidemic, another type of infectious disease emergency, an environmental issue, or an incident of bioterrorism.Reference Aronson and Shope ⁵ The terms outbreak and epidemic are used interchangeably and sometimes together by many epidemiologists and in the professional literature.Reference Green, Swartz and Mayshar ^{6 , 16 ,} Reference Macera, Shaffer and Shaffer ¹⁷ There are scientific articles in which the title indicates an epidemic, while in the body of the paper the episode is called an outbreak.Reference Green, Swartz and Mayshar ⁶

However, the general population tends to perceive the term epidemic somewhat differently from that intended by epidemiologists. According to the CDC, the public is more likely to think that epidemic implies a crisis situation. ¹⁶ The popular literature uses the term epidemic to indicate an outbreak associated with greater risk and greater danger to the public and striking a large number of victims.Reference Green, Swartz and Mayshar ⁶

The declaration or nondeclaration of an epidemic entails different risk framing, possessing different risk signaturesReference Petts, Horlick-Jones and Murdock ¹⁸ in terms of their capacity to engender certain patterns of public understanding. The concept of risk signatures shows that the correlation between scientific terminology and public understanding is not predictable or straightforward. Using the current Ebola episode as a case in point, the terms through which authorities communicate the risk of Ebola, whether as a “mere” outbreak or as an epidemic, influence the response, attitudes, and behaviors of the public. The risk communication approach indicates that public engagement and involvementReference Holmes, Henrich and Hancock ¹⁹ are imperative, stressing the importance of building trust with the publicReference Cvetkovich and Lofstedt ^{20 -} Reference Löfstedt ²² under the unique conditions that prevail during an emerging infectious disease outbreak.Reference Covello ^{23 -} Reference Sandman ²⁵

In risk communication, the health literacy of the public and how the public understands the definitions of scientific phenomena are connected to the Mental Models approach. This approach calls for research to gauge the public’s comprehension of science compared with that of the experts in order to make information more accessible to the public.Reference Morgan, Fischhoff and Bostrom ²⁶

The WHO has defined health literacy as “the cognitive and social skills which determine the motivation and ability of individuals to gain access to, understand and use information in ways which promote and maintain good health.”Reference Nutbeam ²⁷ Health information can be ineffective or even harmful if the public does not possess high enough levels of health literacy to access the information, understand what is being communicated, and appropriately apply it.Reference Root and Stableford ²⁸

The media conveys information about illnesses and outbreaks and mediates the authorities’ decisions and frames to the public. Media literacy is the public’s “ability to access, analyze, evaluate, and produce communication in a variety of media forms.”Reference Zettl ²⁹ One who has developed media literacy will be able to discern the validity and relative worth of information.Reference Brecklin and Hoffman ³⁰

The terms through which an outbreak are communicated and how these terms are understood (media literacy) are crucial. The aim of the present study was to examine in what terms leading newspapers and news sites characterized the Ebola crisis.

RESULTS

Three main findings emerged from the analysis. The first was that both terms, outbreak and epidemic, were used interchangeably in articles focusing on Ebola. The second finding was that the term outbreak was used most frequently. As shown in Table 1, we found that outbreak appeared in 436 of 582 articles (74.9% of all articles), whereas epidemic appeared in 144 (24.7%).

Table 1

Number of Articles That Used the Terms Outbreak, Epidemic, Pandemic, Disease, Virus, and Other to Describe Ebola in The New York Times, Daily Mail, and Ynet Before and After President Obama’s Speech

An examination of each newspaper separately showed that in both English-language newspapers, outbreak was more prevalent. In The New York Times, the term appeared in 65 of 80 articles (81.3%), while the term epidemic appeared in 17 articles (21.3%). Similarly, in the Daily Mail, outbreak appeared in 356 of 444 articles (80.2%), while epidemic appeared in 102 (23%). In contrast, on Ynet, epidemic was more prevalent. It appeared in 25 of 58 articles (43.1%), while outbreak appeared in 15 (25.9%).

Furthermore, we found that in 31 articles published in the 3 newspapers, both terms were used interchangeably in the same article, sometimes even in the same sentence. This occurred in 24 of 444 articles in the Daily Mail (5.4%), 3 of 80 articles (3.8%) in The New York Times, and 4 of 58 articles (6.9%) on Ynet. For example, in an article from July 27, 2014, in The New York Times, Reference Nossiter ³⁸ both terms are used: outbreak is used in the subheading of an accompanying video: “Amid the deadliest Ebola virus outbreak in history, doctors are fighting the disease and also local populations’ fear of medical treatment.” In the body of the article, epidemic is used: “Health workers here say they are now battling two enemies: the unprecedented Ebola epidemic…and fear.” In an article from September 17, 2014, in the Daily Mail, Reference Parry ³⁹ outbreak and epidemic are used in the same sentence: “The U.S. yesterday vowed to deploy 3,000 armed troops to Liberia, the country hardest hit by the outbreak, to help tackle the epidemic.” In a small percentage of the articles, 5.5% overall (32 articles), neither outbreak nor epidemic was used. Instead, we found the use of other terms, including disease, virus, spread, and in one case, pandemic.

The third finding that emerged is that there was a noticeable increase in the use of epidemic from September 16, 2014, corresponding to the date of Barack Obama’s speech about Ebola, explicitly calling it an epidemic. As shown in Table 1, prior to Obama’s speech, 86.8% of the articles (323 of the 372 articles published before the speech) used outbreak and only 8.6% (32 out of 372) used epidemic. The articles published after his speech showed a greater use of epidemic, such that both terms were used nearly to the same extent: 53.8% of the articles (113 of the 210 articles after the speech) used outbreak and 53.3% (112 of the 210 articles after the speech) used epidemic.