Monday, 7 April 2014

Ebola virus disease (EVD) outbreak in West Africa: chart of cases to 04-Apr

Data are based on WHO DONs, French Embassy Conakry
 figures and WHO Tweeted information.
Click on image to enlarge.
The Ebola virus disease (EVD) case chart adjacent is based on the latest Disease Outbreak News (DON) from the World Health Organization (WHO) posted at the Global Alert and Response (GAR) site [1] and at the African Regional Office (WHO-AFRO) [2].

There are roughly 163 suspected, probable and laboratory-confirmed cases including 95 deaths (58.3% proportion of fatal cases) for which only 56 (34.4%) have been confirmed by laboratory tetsing.

I'm also maintaining a curated Storify timeline here which lists some key Tweets and links on this outbreak. 

A few things to note about the chart and the outbreak:

  1. The susp/prob/conf (shorthand I use on Twitter) numbers change - the 1st 2 numbers can go down as well as up as cases that cannot be laboratory confirmed as due to EVD are discarded from the tally. Other diseases with similar presenting signs and symptoms occur in the West African region so this is not at all unexpected. We see the same thing for other viral outbreaks, like influenzavirus, all the time.
  2. The WHO does not posted "grand totals". The DONs present totals for each region (currently Guinea, Sierra Leone and Liberia), which I've tallied up above.
  3. Its worth remembering that this outbreak was happening back in early Feb, so there was a passage of time during which people were exposed and did not know precisely what was causing illness. This creates a lag between the time of the first announcement and when the situation can come under some semblance of control. Control requires that the various teams arrive, are coordinated and set up in the area to test, trace, educate and reduce virus spread. Each time a new region has a case, the same flurry of activity may well ensue, so case numbers will seem suddenly spike - but as we can see, they do not continue to rise exponentially, or even at all in some regions. This is thanks to the expert teams including those from the WHO, jurisdictional Ministries of Health, UNICEF, the Red Cross and Médecins Sans Frontières (apologies to all those I've missed - you are all doing a fantastic job under extreme conditions and you are extremely  appreciated)
  4. Posts on this outbreak do not occur daily - I presume, as for avian influenza virus outbreaks etc, posting of numbers is based on when those data are collated, summarized and provided to the WHO.
  5. There are reports of 4 haemorrhagic fever cases from Mali (some of whom had traveled to Guinea; a suspect case is also reported in Ghana coming from Mali although there are questions about where from precisely) that are not, at writing, laboratory confirmed.[5] Samples are being sent to the United States for confirmation. Why not to the Institute Pasteur in Dakar, or Guinea field labs I do not know; presumably because of pre-existing arrangements?
  6. Liberia has 1 suspected EVD case in a hunter who seems to have acquired his infection locally (no contact with know EVD cases or with Guinea). This suggests to me that the vector is actively infected in the region. Perhaps this is a migratory season (seasonal change, following food sources, breeding) for this Ebola virus's animal hosts, previously found to be fruit bats, chimpanzees, gorillas, monkeys, forest antelope and porcupines in particular, eaten as "bushmeat". I admit to knowing nothing about animal movement in the region however.
  7. While EVD is "highly contagious", close contact with an infected animal host or an infected human cases' bodily fluids (blood, organs, mucous, urine, vomit, faeces and semen for up to 7-weeks post-infection) is required to acquire an infection. Generally the virus doesn't spread across distance as well or quickly as for example, influenzavirus does. This is largely because the virus is not spread the same way:
    • Sneezing and coughing is not considered a method of EVD transmission
    • Once the patient is symptomatic, they do not move around as much; from that point, spread of the virus to new people requires those people to come to the ill person. This is why healthcare workers, especially early on in an uncharacterized outbreak, and close family members caring for an ill or deceased relative number highly in new cases of EVD. 
    • Basic levels of infection prevention and control can interrupt transmission. These include good hand hygiene, use of personal protective equipment and prevention of needle stick injuries.
  8. Airborne transmission is not considered a risk factor for acquiring EVD; this is not the movie Outbreak where the fictional "Motaba" virus mutates into an airborne ebolavirus-like pathogen. Also unlike the movies, bleeding from orifices and the skin can occur, but much more rarely than the movies lead us to believe
  9. EVD signs and symptoms start suddenly 2-21-days (8-10 more common[3]) after virus acquisition and usually include fever, headache, joint and muscle aches, weakness, diarrhoea, vomiting, stomach pain, loss of appetite and may also include rash, sore throat, red eyes, hiccups, cough, chest pain, breathing and swallowing difficulties and sometimes internal and external bleeding. Not everyone dies from infection however the higher end of the mortality spectrum for the species Zaire ebolavirus can reach 90% in outbreaks with >1 case identified.[4]
  10. A person with no signs or symptoms of disease is not considered contagious.
  11. While a border closure (Senegal) and some flight restrictions have come into play, these may only serve to disadvantage the outbreak region rather than provide any true risk mitigation. Closing a border may hinder the flow of food, medical supplies and daily goods as well as interrupting the normal commerce of the country, impacting both economically and directly on the lives of the overwhelming majority of people who are not infected. I'm not aware of any evidence that shows closing a border has any reducing effect on an Ebola outbreak. Closures are a knee-jerk reaction caused by the fear of a scary disease.
And that last point is an important one. Ebola evokes some scary images outside of Africa. And so it's important for us not to run around like a decapitated Gallus gallus domesticus. We need to rein in the excessive over-reaction. As Maryn McKenna aptly noted recently over on Superbug, many things are killing more people, more regularly every day both in and outside of Africa. Having said that, I can totally understand the reactions of those living inside of West Africa just now. Among them, those who both have or have never looked this pathogen in its filovirusy-eye and stared down the barrel of its disease before. 

Viruses can be pretty scary things indeed.

  1. WHO Global Alert and Response (GAR) Disease Outbreak News (DONs) Articles
  2. WHO African Regional Office (WHO-AFRO)
  3. Signs and symptoms of EVD or Ebola haemorrhagic fever (HF) from US Centers for Disease Control and Prevention
  4. WHO EVD fact sheet
  5. WHO AFRO EVD West Africa SitRep for 4-April-2014
  6. A Patient in Minnesota Has Lassa Haemorrhagic Fever. (Don’t Panic.)

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