The proportion of fatal cases (PFC)…

In July 2013 I coined an initialism for Virology Down Under (VDU) to avoid using the term Case Fatality Ratio/Rate/Risk (CFR); the Proportion of Fatal Cases
(PFC).
IMPORTED POST*

I use the term on VDU and have published it an article. I have no expectations that anyone else will use it although I notice it made an appearance in a HeathMap story.

The PFC is a percentage calculated as the currently known number of fatalities divided by the number of total lab-confirmed cases including fatalities, regardless of whether surviving cases are inpatients (hospitalised) or outpatients.PFC

The PFC is just a number – it’s not meant to imply the inclusion of every case that ever happened – it never could. It does not account for those cases who will die early and without sampling, or who will later on, either directly or indirectly, as a result of their infection but who may be alive at the time of calculation. 

The PFC is a snapshot to be used before an outbreak is done and dusted. The PFC is a guide to what is happening right now using the data we can access. Sometimes that means lots of data, sometimes they are very limited or rapidly changing or inaccessibly behind closed doors.

The CFR makes use of the number of recovered cases in its denominator.[3] So it’s important to know survivor numbers. As suggested above, this requires that all the people who will recover from their infection, have recovered (and been discharged). 

Using the CFR early in an emerging virus/disease outbreak, when what usually brings an outbreak to our attention is death, is great for selling papers, but not helpful or accurate or even possible sometimes. 

The CFR is most useful at the end of an epidemic/pandemic. Before that, CFR creates unwanted expectations when data-in-hand are poor or rapidly changing early in an outbreak. 

Some will take a PFC and multiply it by the world’s population as an estimate of how many are going to die if virusX reaches pandemic levels. That’s not helpful or accurate. Just accept the PFC as that snapshot of what’s happening now.

References

  1. Age-specific and sex-specific morbidity and mortality from avian influenza A(H7N9).
    http://www.ncbi.nlm.nih.gov/pubmed/24091087
  2. Estimating the fatality of the 2014 West African Ebola Outbreak
    http://www.healthmap.org/site/diseasedaily/article/estimating-fatality-2014-west-african-ebola-outbreak-91014
  3. Case fatality rate
    http://en.wikipedia.org/wiki/Case_fatality_rate

Updates

  • This post was excerpted and altered a little, from a more influenza A(H7N9) virus slanted article to be found here. I thought it deserved its own page.

*Imported Post

  1. This post from 14SEPT2014 was posted over on my old blog platform virologydownunder.blogspot.com.au. It has now been moved to here and lightly updated. 

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