When you say flu, what do you really mean?

Everyone knows the 'flu when they see it. Its like the cold but only worse, right? But often the public are very quick to brand something the flu when it clearly isn't and this even extends to doctors in the clinic. As highlighted by this recent paper, published in BMC Infectious Diseases.

BioMed Central | Full text | During the summer 2009 outbreak of "swine flu" in Scotland what respiratory pathogens were diagnosed as H1N1/2009?

Turns out a lot of viral infections look like influenza, clinically. But what are doctors misdiagnosing as flu? Based on this study, which paired molecular diagnostics with what the clinic thought each patient had  based on well-defined guidelines (mostly flu at the early stages of the 2009 swine-influenza pandemic - April - July).

Are these symptoms clinically specific to influenza infections? http://symptomswineflu.com 

What they did was:

We examined the results from 3247 samples which were sent to the laboratory during April-July 2009

And,

Real-time RT-PCR was carried out in order to detect influenza A (a generic assay and a H1N1/2009 specific assay [7]), B and C, RSV, rhinovirus, parainfluenza 1-4, human metapneumovirus, coronavirus (229E, NL63, HKU1 and OC43), adenovirus, and Mycoplasma pneumoniae.

 Out of the 3247 samples analysed, 27.9% were diagnosed as being infected with a respiratory pathogen they looked for, what is causing their symptoms??. While human rhinovirus infections were the most common, H1N1 influenza infection was one of the least common at 0.8%. A whole heft of viral and bacterial pathogens were detected at levels intermediate to these.


So, whats going on here? How come it's so difficult to diagnose these guys and after-all, does it really matter?


Well, this work highlights the difficulty in accurately determining the causative pathogen from basic symptoms. The viruses looked at in this study all share replicative and epidemiological characteristics: respiratory pathogens, infect the upper/lower respiratory tract and, as viruses, induce a general interferon/inflammatory response (sore throat, headache, malaise, fever, muscle pains etc.) and are transmitted among the winter/spring months. It is not until you look at the molecular level, that you realise they are all at least slightly different.


And, yes it does really matter. Many of these people may have developed life-threatening symptoms as a consequence of an infection that was not influenza and would have been missed by the clinicians. Also, at a great cost to society and the patient (financial, medical and emotiona;), some people were wrongly treated with antiviral medication after being diagnosed swine flu.


What studies like this show, is the importance of molecular diagnostics in times of pandemic infections. But the problem here is that, despite their high specificity, they can be expensive and difficult to run, especially in 'field' locations across the world.