Tuesday, June 23, 2009

Sense And Sensitivity

 

 

# 3380

 

The approach to the identification and treatment of the novel H1N1 swine flu differs from one country to the next, and in some countries, from one region of a country to another.

 

Physicians in London and Birmingham (but not all of the England) have now been asked to begin diagnosing swine flu by clinical assessment (by symptoms) instead of waiting for laboratory tests.

 

The debate over relying on laboratory tests vs. going with a doctor’s clinical assessment (or `sense’) is an old one, and not restricted to this flu outbreak.   Most doctors recognize the importance of treating the patient, not the lab report.

 

Unfortunately, there are a plethora of pathogens that can produce influenza-like symptoms in a patient.  Parainfluenza, respiratory syncytial virus, metapneumovirus, influenza B, and adenovirus are just a few, and differentiating between them is nearly impossible.

 

Luckily, this time of year in the northern hemisphere, most of these viruses are near their low ebb for the year.   During the winter, when these viruses abound, it becomes much more difficult discerning which are influenza `A’.

 

Relying on testing is not without its problems, however.

 

The first line of testing, commonly done in a doctor’s office, is rapid influenza test kit, which generally just tells the doctor if you have an influenza `A’ or `B’ virus.  

 

These tests only detect the Influenza `A’ virus about 70% of the time (sensitivity), which means 30% of those with the flu will come away with a negative test.   Additionally, they can produce a `false-positive’ reading (specificity) between 5% and 10% of the time.

 

In Japan, they went back and did laboratory testing (see Japan: Rapid Influenza Test Sensitivity) on those who initially tested negative with the laboratory test, and found that about 30% actually had the H1N1 swine flu.

 

Additionally, it can takes several days to get results back from a laboratory, and as the number of suspected cases increases, those delays increase.

 

Obviously there is no perfect solution here, which explains the different approaches being tried across the UK.  

 

In the UK, they are still working in `containment mode’, and so trying to identify all cases is a bit more important than here in the United States, where if you present with flu-like illness this time of year, the presumption is that you probably have swine flu.

 

 

 

London GPs told to diagnose swine flu clinically

23 Jun 09

By Steve Nowottny

GPs across London have been told to use clinical assessment rather than laboratory testing to identify cases of swine flu, in a major shift in the strategy for combating the outbreak.

 

A new algorithm for GPs across the capital, which came into effect yesterday afternoon, instructs them to prescribe antivirals for all symptomatic patients who live in the capital, without waiting for the results of swabs.

 

Swabs should continue to be taken for suspected cases who are not household contacts of a laboratory confirmed case.

 

An HPA spokesperson said that a similar approach has also been adopted in some parts of Birmingham, centre of one of the largest outbreaks in Europe – although she said 'the changes in treatment are not widespread across the county'.

 

However, a Scottish Government spokesperson confirmed that clinical assessment has now been abandoned north of the border, with laboratory testing continuing for all cases. Health Secretary Nicola Sturgeon said last week that clinical diagnosis ‘has not proven to be as effective as originally thought’.