Age and sex morbidity and mortality from avian influenza A(H7N9) virus

Click to enlarge. The majority of cases of H7N9 that occurred
worldwide earlier in 2013. Taken from Virology Down Under's
H7N9 page.

In a study co-written by yours truly using a lot of data collected for Virology Down Under, Dr Joseph Dudley and I have just described, in the Journal of Clinical Virology, the age-specific and sex-specific morbidity and mortality from the avian influenza A(H7N9) virus outbreak earlier in the year.

We sought to highlight differences between H7N9 and another zoonotic influenza A virus, H5N1. The distribution of age and sex is notably different between cases of each virus in more distant countries (Saudi Arabia vs Egypt) as it is within the same country (see Cowling et al reference in the article's discussion). Such differences and patterns may be instructive for identifying specific risk factors for an outbreak and also serve to highlight that there are differences between outbreaks which, on the surface, might be expected to have very similar courses. 

Intriguingly, there were marked similarities between H7N9 and Middle East respiratory syndrome coronavirus age and sex case distribution.

We also published the term created here on VDU, the Proportion of Fatal Cases (PFC). A percentage defined as the number of currently known fatalities divided by the number of total lab-confirmed cases including fatalities, regardless of whether they are inpatients (hospitalized) or outpatients. It was created to avoid the need for a gauge of recovered cases (released from hospital) which is linked with use of the term Case Fatality Ratio.

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Stuff from the literature: Don't judge a virus by its worst case [UPDATE].

This article, a Letter in the Journal of Clinical Virology (2013 Sep; 58(1):338-9) is one from our own keyboard. It is entitled Avian influenza A (H7N9) virus: Can it help us more objectively judge all respiratory viruses? Unfortunately it s behind a paywall, but I do not have the funds (they all go into the research) to pay for open access publication.

We try and make the point that every respiratory virus can be found in severe, moderate, mild cases or even asymptomatic people - H7N9 in a young child earlier this year being an example - but no particular portion of a given virus's clinical severity spectrum should be used to define that virus.

The risk of future prejudgement is real. For example, not all influenza-like illness (ILI) is due to influenza viruses. Expecting it to be so leads to confusion and misunderstanding. But on the other hand, screening for every likely viral culprit in every patient during a pandemic is impractical - or at least, it creates a bottleneck that slows result reporting and infection control. At some stage we'll have better, faster higher-throughput tech to do this, but we're not there yet - so we have to pick and choose.
In the meantime, old labels like the "common cold" virus (human rhinoviruses and coronaviruses) have done little to help anyone really be aware of what a virus is capable of. You may argue they have slowed research into their other roles to the detriment of public health. I do. These labels will never be shaken off. Yet we now know that most asthma exacerbations are triggered by infection with one of these 200 or so little packets of mischief.
Apart from naming viruses to avoid geopolitical, and personal sensitivities, it is also important not to label viruses which at one time may be innocuous...and at another, deadly.

Viruses pack a lot of potential into a small shell-and do a great job of running us in circles.

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