On 9/23, WHO published a paper in the New England Journal of Medicine that looked back on the spread of the disease and offered some insights as to where they think the virus could go from there. The abstract conclusion was: “These data indicate that without drastic improvements in control measures, the numbers of cases of and deaths from EVD are expected to continue increasing from hundreds to thousands per week in the coming months.”
The paper shed some light on some of the categorizations of Ebola cases. A suspected case is described as “illness in any person . . . who has (or had) sudden onset of high fever and had contact with a person with a suspected, probable, or confirmed Ebola case or with a dead or sick animal; any person with . . . high fever and at least three of the following symptoms: headache, vomiting, anorexia or loss of appetite, diarrhea, lethargy, stomach pain, aching muscles or joints, difficulty swallowing, breathing difficulties, or hiccupping; or any person who had unexplained bleeding or who died suddenly from an unexplained cause.” Ebola is said to be accompanied by a sudden fever of 101.5 or higher. Interestingly, it was hiccuping that led researchers initially confronting the disease to suspect Ebola instead of other diseases more common in west Africa.
A probable case is described as “illness in any person suspected to have EVD who was evaluated by a clinician or any person who died from suspected Ebola and had an epidemiologic link to a person with a confirmed case but was not tested and did not have laboratory confirmation of the disease.” So a probable case is essentially a person suspected of having Ebola who was either seen by a health care worker or who had a link to a confirmed case. Confirmed cases are, logically, cases that were confirmed by a laboratory.
Testing people for Ebola is not simple. There are a limited number of labs that can handle Ebola testing, a limited number of couriers who will handle the blood samples on the way to the labs, and simply an overwhelming number of cases. The focus has been on treating the ill rather than making sure that every case is laboratory confirmed. This focus shift has also led to a gross under-counting of Ebola cases and fatalities as contact tracing has begun to give way in Liberia and Sierra Leone to an emphasis on treatment.
An analysis of the most common symptoms in confirmed or probable cases was detailed. Fever is the most common, appearing in 87.1% of the analyzed cases. “[F]atigue (76.4%), loss of appetite (64.5%), vomiting (67.6%), diarrhea (65.6%), headache (53.4%), and abdominal pain (44.3%)” were the other common symptoms. The infamous unexplained bleeding was found in less than 18% of cases.
Death rates were determined to be 70.8% when looking only at cases with a definitive outcome (death or recovery). Among health care workers, Guinea fared the best at 56.1% fatality while Liberia fared worse with 80%. Guinea had come into the outbreak with the most developed health care system among the three countries most affected and Liberia was the least developed, with only one doctor per 100,000 people. Sierra Leone was better, but still only had two doctors per 100,000 (2010 numbers). For comparison, the US has 245 doctors per 100,000 people.
The average incubation time is 11.4 days, with 95% of cases showing symptoms within 21 days after exposure. The R value, or number of additional people infected by each infected person, remained over 1 for each of the 3 most affected countries. If the value is lower than 1 then that means that the epidemic is in decline (that each infected person infects less than one other person). If it is 1, each infected person spreads it once, statistically, holding the epidemic steady. If the R value is higher than 1, each infected person spreads it to more than 1 other person, and keeps the epidemic expanding to an ever increasing number of patients.
The WHO also spoke of the chance that Ebola may become endemic in west Africa. This would mean that Ebola would always be present in the human population in the region. As long as Ebola would be endemic the risk of a spread to other countries would continue indefinitely, and we have seen that already the disease is capable of worldwide transmission.
