Is this year's Strep A outbreak really worse than normal?

For lockdown sceptics, these tragedies are the chickens coming home to roost.

In reality, it is too soon to say whether that the current Strep A outbreak actually is deadlier than previous years or that youngsters are unusually susceptible to fatal complications as a result of reduced exposure.

READ MORE: Scottish Strep A cases 'likely to rise' over coming weeks 

If this seems counterintuitive, it is important to unpack what is really going on behind the headline figures - which are inevitably alarming for parents.

In England, where there have been 14 deaths in children, the number of invasive Group A streptococcal infections (iGAS) - the form of the disease that can cause serious illness - reported between mid-September and the end of November has been more than double the average for the previous five years: 652 compared to 311.

Typically the season peaks between March and June, so there is an expectation that a high number of cases now will result in far fewer than normal in Spring.

Similar post-pandemic unseasonal patterns have been seen in for respiratory viruses such as RSV.

The key question is whether, by the end of the ‘season’ in September 2023, the case-fatality ratio is any higher - in other words, what percentage of known iGAS cases resulted in a death?

Number of iGAS notifications, England, per week, from 2017/18 season to 2022/23 season to date (Image: UK Government)

Pre-pandemic, the ratio was around 10 per cent. In 2017/18, for example, there were 370 iGAS deaths out of 2,967 notifications of the disease in England. In 2018/19, the case-fatality ratio was 9.1%.

To date, for 2022/23, it has been around 9.3%, with around 60 iGAS deaths in total across all age groups.

A larger proportion of deaths than usual have occurred in under-15s - around 20% compared to roughly 10% on average.

However, even in this age group, that does not necessarily mean that the case-fatality ratio is any higher.

For example, preliminary data indicated that the iGAS rate per 100,000 had been nearly five times higher in the one to four age group compared to the same period in 2017 to 2019.

READ MORE: 'Needle spiking', social panics, and mass psychogenic illness 

Such an unusually high rate in a comparatively short period of time would inevitably translate into a ‘clustering’ of deaths that seem out of the ordinary and frightening.

We have already seen something similar this year with the sudden spike in acute paediatric hepatitis cases during March and April, first spotted in Glasgow.

Worldwide, children - mostly under five - were admitted to hospital with liver failure, some requiring liver transplants and some sadly dying.

At first, it was a mystery. None of the children tested positive for the common hepatitis viruses, and no link to environmental or chemical toxins was found.

As scientists began to unravel what was really going on, a possible link to adenovirus emerged: the spike in acute paediatric hepatitis appeared to have overlapped with a surge in adenovirus infections in young children as Covid restrictions had been lifted.

This led to speculation that they had been left more vulnerable to severe complications due to a lack of exposure during the pandemic - the so-called ‘immunity debt’ theory.

In fact, this now looks to have been a red herring.

On the one hand, lockdown did create a situation in which an unusually large number of young children were not exposed to adenovirus for around two years, making them susceptible to the virus once social mixing did resume.

However, this did not mean they were actually more vulnerable to it; only that the sudden spike in case rates in a short period created a clustering effect.

As a result, an unusually high number were hospitalised around the same time with the same symptoms - triggering a public health alert.

READ MORE: The inside story of Scotland's child hepatitis outbreak 

Pre-pandemic, children would be hospitalised every year with unexplained acute hepatitis - but cases would normally be more spaced out.

Ironically, lockdown shed light on something that had been occurring largely unnoticed for years.

Investigators now believe that the actual cause of these “mysterious” paediatric liver disease cases is something called adeno-associated virus 2 (AAV2) - a previously little understood ‘bystander’ virus which can lie dormant in the body for years until ‘activated’ by adenovirus.

It remains to be seen how this year's Strep A season will ultimately play out - but there is currently no evidence that the strains in circulation have mutated to become any more virulent, for example.

Likewise, while laboratory reports in Scotland of upper respiratory Strep A infections - a proxy for scarlet fever - are much higher than normal, this is not translating into a comparable surge in iGAS.

Scarlet fever is characterised by a very sore throat, a sandpaper-like rash, fever, and headache, but can be treated with antibiotics.

In very rare cases, the bacteria enters the bloodstream - causing iGAS - which can be life-threatening. Symptoms include dizziness, confusion, low blood pressure and abdominal pain.

Scarlett fever notifications have shot up well above pre-pandemic peaks, but the number of notifications for iGAS in Scotland remains below the highs seen in some previous years (Image: PHS)

According to Public Health Scotland, there were 818 scarlet fever reports in the week ending December 11 compared to 160 to 270 per week in previous years' peaks.

In comparison, there were six newly confirmed iGAS cases across all age groups compared peaks of 12 to 18 per week in previous years.

This suggests that publicity is leading to more people seeking tests, which means unusually high numbers of scarlet fever cases are being detected, piling pressure on antibiotic supplies - but that, so far, iGAS cases in Scotland have not yet reached the levels seen during previous years' outbreaks.

If lockdown is to blame for anything, it is disrupting the normal seasonal patterns of disease in way that induces panic - rather than genuinely worse infections.