Every year in the UK we have an increase in respiratory illnesses in the winter, in particular with influenza. So how do we know when it is flu-season? There is a threshold based upon the observations and testing of patients in certain sentinel GP practices and laboratories around the country and when they are seeing enough cases of influenza it means that the winter virus is here. This year is no exception, and we are now seeing a lot of cases of influenza therefore we are allowed to prescribe Oseltamivir (Tamiflu) based upon the clinical suspicion of influenza. Out of season a confirmed laboratory test is usually required. In fact influenza is circulating in the community at levels higher than the last three years and there have been 74 outbreaks reported nationally in the last week according to Public Health England, 60 in care homes.
If you see a patient who has influenza like symptoms (fever plus cough, sore throat, rhinorrhoea, headache or myalgia) then it is now very likely that they actually do have “Flu” (not RSV which was more common just before Xmas). There are lots of viruses that can give a flu-like illness such as Parainfluenza, Respiratory Syncytial Virus and Rhinovirus. Best practice is to send a viral swab form the nose and throat then start an anti-influenza drug. Anti-influenza drugs are neuraminidase inhibitors which can reduce the duration of symptoms in patients with influenza (by 1 day), if they are started within the first 24-48 hours of the illness. There is therefore some economic benefit to treating all patients with influenza enabling them to return to work earlier. However treatment started after 48 hours makes little difference and there is no evidence that they (as previously claimed by the drug company) reduce mortality. Timing is critical and GPs may not feel anti-influenza drugs offer a sufficient window of opportunity for treatment.
Why do winter outbreaks occur?
One of the reasons why we see new strains of Influenza Viruses causing infections every year is that Influenza A can undergo antigenic drift and antigenic shift:
- Drift is due to small changes in the genetics of the virus, meaning people become infected but as they have experienced a similar virus their bodies can recognise a large element of the new virus. Relatively few people are infected and have milder symptoms. This is seasonal flu, which genetically changes slightly but continuously
- Shift occurs when the virus acquires new genes from a different Influenza Virus. This creates a new virus people have not been exposed to yet, capable of causing a pandemic. Pandemic “Swine Flu” and “Bird Flu” are examples of antigenic shift in an animal, e.g. the pig had both human and avian flu and genes swapped between them to create a new Influenza Virus. These pandemic viruses tend to become the “next” seasonal virus after the population has been exposed
The vaccine is based upon predictions by the WHO of which viruses are impending and is then developed for the global market. In the UK in recent years Influenza A causing seasonal flu has been H1N1, however this year the majority of laboratory confirmed Influenza A has been H3N2 (70%). There is some evidence from Australia and the USA that this current H3N2 strain is poorly covered by this year’s influenza vaccine. To date the PHE has genetically analysed 24 Influenza A isolates and only found 5 with the potential to break through this year’s vaccine, however as flu-season is just beginning we may see a higher vaccine failure rate in the coming months. Even though this year’s H3N2 is different to the vaccine’s H3N2, this is still only due to antigenic drift not a shift which might lead to a pandemic. Giving this year’s vaccine is still important as it could have prevented 19 of the 24 H3N2 viruses analysed by PHE.
Secondary bacterial infections
Influenza has been causing infections for the last few weeks, but now we are seeing the secondary bacterial infections which are often more severe than the influenza itself. It is likely that the inflammation in the upper respiratory tract caused by influenza makes it easier for the upper respiratory tract normal flora to invade and cause infections. Watch out for the classic organism and infection combinations seen following influenza:
- Streptococcus pneumoniae causing pneumonia or meningitis
- Haemophilus influenzae causing pneumonia (the name even gives a big clue that influenza can predispose to this infection!)
- Group A Beta-haemolytic Streptococcus (Streptococcus pyogenes) causing cellulitis or necrotising fasciitis
- Neisseria meningitidis causing sepsis or meningitis
Influenza infection control
As influenza season is upon us and the virus is easy to spread, what should be done to limit its impacts in our communities, hospitals and care homes? The most important aspect of the management of influenza is to try and prevent transmission. If anyone has a respiratory infection, whether it’s influenza or not, they should be encouraged to follow the Public Health England advice for when they cough or sneeze:
Catch it. If you cough or sneeze then use a tissue.
Bin it. Throw the used tissue into a bin; don’t keep it to reuse it later.
Kill it. Wash your hands with soap and water to kill the virus.
In schools and healthcare settings best practice infection control measures include:
- Oseltamivir or Zanamivir should be started as early as possible, ideally within 48 hours of the onset of symptoms
- The current vaccine may not be that good at preventing the current strain of Influenza A
- Influenza leads to potentially serious secondary bacterial infections
- Think about preventing transmission. It may sound simple, Catch it. Bin it. Kill it. If everyone did it then it would be a very effective way to control influenza. Can't remember it? Try this catchy rap and dance moves!! ...it takes a little while to "warm up" bear with it...you'll be singing it all night!