In wake of COVID, scarlet fever and invasive strep cases soar in UK


A microscope image of <em>Streptococcus pyogenes</em>, a common type of group A strep.
Enlarge / A microscope image of Streptococcus pyogenes, a common type of group A strep.

Scarlet fever is spiking in the UK, with case numbers more than four-fold higher than normal for this time of year. And a rare but serious invasive disease caused by the same bacteria that causes scarlet fever and strep throat—Group A streptococci—is also surging, killing at least eight children in the UK, according to media reports.

The unusual rise is seen as yet another anomalous disease transmission cycle rippling in the wake of the COVID-19 pandemic. Like many other seasonal infections, scarlet fever cases in the UK virtually flattened at the end of 2019–2020 season and bottomed the chart throughout the 2020–2021 season, according to data released by the UK Health Security Agency.

Now, with most pandemic-related health restrictions lifted or at least eased, a throng of seasonal infections—particularly those that hit children the hardest—have returned. Many have returned with some ferociousness, finding a yet larger pool of susceptible victims than usual after a hiatus. Many of these disease-cycle anomalies have been seen in seasonal viruses, namely enteroviruses, adenoviruses, influenza, and RSV (Respiratory syncytial (sin-SISH-uhl) virus), which are currently swamping hospitals and pediatric wards in the US.

“Lots of infections became rarer during the restrictions of the recent pandemic and are now coming back rapidly as mixing normalizes,” Adam Finn, a pediatrics professor at University of Bristol, said in a statement. “[Group A strep] is no exception, and we have been seeing increasing numbers of cases in recent months.”

Infection connections

Transmission of group A strep bacteria is associated with the transmission of viruses. Historically, group A strep infections are closely linked to the spread of chickenpox, though clinicians note that a strep infection can strike after other viral infections. It’s unclear what the link between certain viral infections and group A strep is, exactly. Researchers have hypothesized a confluence of factors may explain the link, from overlapping timing in disease cycling, similar transmission routes (e.g. respiratory), and a common age of victims.

There’s also the possibility that some germs share common methods of suppressing the immune system in order to spark an infection. Thus, infection with one germ could pave the way for another that takes a similar route. There is some evidence for this with chickenpox and group A strep, which similarly alter the activity of certain T cells. But some viral infections also suppress the immune system more generally. Perhaps the best example of this is measles, which suppresses immune response for weeks to months after an infection, leading to what some experts call “immune amnesia.” Prior to childhood vaccination campaigns, spread of measles was closely associated with upticks in cases of whooping-cough (pertussis), which is caused by the bacterium Bordetella pertussis.

The current rise of group A strep infections in the UK is not clearly linked to a rise in chickenpox cases. Chickenpox is not a notifiable disease in the UK, meaning official counts are not available. However, sentinel surveillance data suggests that there hasn’t been an unusual rise.

The rise of strep A is coinciding with viral respiratory infections, though.

“Usually we see a high number of [group A strep] cases in late spring or early summer, often after chickenpox infections,” Elizabeth Whittaker, a pediatric infectious diseases and immunology expert at Imperial College London, said in a statement. “High numbers at this time of year are unusual and probably occurring as normal seasonality has not yet returned… We are seeing more pneumonia than usual, most likely as group A strep infections are coinciding with the peak in winter respiratory viruses which are typical for this time of year.”

Group A strep infections typically cause mild infections such as strep throat, scarlet fever, and the skin infection impetigo, which are effectively treated with antibiotics. In the UK, there were 851 cases of scarlet fever in week 46 of this year (ending on November 19), whereas the average for the previous years was 186 cases in week 46, the UKHSA reported. The spike is part of a larger rise; there were 4,622 notifications of scarlet fever in weeks 37 to 46 this year in England, compared with an average of 1,294 in the same period in the previous five seasons.

Severe cases

In rare cases, group A strep can get into the bloodstream, causing a severe, invasive disease called invasive Group A strep (iGAS), which can be deadly in young children. So far this year, the UKHSA has tallied 2.3 cases per 100,000 children ages 1 to 4 compared with an average of 0.5 in the pre-pandemic seasons (2017 to 2019), and 1.1 cases per 100,000 children ages 5 to 9 compared to the pre-pandemic average of 0.3 at the same time of the year.

The severe cases remain rare, but identifying strep A infections may be more difficult than normal this year as it circulates among respiratory viruses, potentially delaying treatment.

“Severe invasive group A strep is rare, and parents don’t need to worry, but do need to be aware when and how to seek medical attention,” Whittaker said. “We would normally expect fevers due to viral infections to settle within 4 or 5 days, so if they are persisting, or are associated with lethargy, difficulty breathing, poor drinking or wet nappies/urine output, families should get in touch with NHS111 for advice,” referring to a non-emergency medical service line in the UK.

“Prompt treatment with antibiotics can manage these infections, but it is important they are recognized and treated quickly,” Nathalie MacDermott, a pediatric infectious disease expert at King’s College London, said. “Prompt treatment of scarlet fever and strep throat also reduces the chances of a child developing invasive Group A Strep and reduces the chances of the infection spreading to other children at school or household members.”

In the US, scarlet fever is not a notifiable disease—so there are no official numbers—but there is surveillance of iGAS cases. In a press briefing earlier this week, Barbara Mahon, an epidemiologist with the Centers for Disease Control and Prevention, said, “As far as I’m aware, we have not heard of any notable increase [in iGAS cases].”


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