What’s behind the recent surge in strep A and scarlet fever?

One explanation could be that a recent spike in respiratory virus infections has left people more susceptible to infection with group A streptococcus.

  • 6 January 2023
  • 5 min read
  • by Linda Geddes
Woman checking her son's fever. Credit: MART  PRODUCTION
Woman checking her son's fever. Credit: MART PRODUCTION


At least five European countries have reported an increase in invasive group A streptococcus (iGAS) infections in recent months, and in some cases, scarlet fever. The US Centers for Disease Control and Prevention (CDC) is also investigating a possible increase in iGAS disease in the United States. An increase in iGAS-related deaths has also been reported in some of these countries. In all cases, children under ten have been the most affected age group.

Despite a moderate increase in iGAS-related infections and deaths in some countries, the WHO currently assesses the risk for the general population as “low”.

Streptococcus bacteria come in various forms and can trigger an array of symptoms from a mild sore throat to pneumonia, or life-threatening blood and organ infections. Group A streptococcus infections are caused by Streptococcus pyogenes – strep A – bacteria. These organisms often live harmlessly on people's skin or in their throat lining, but can sometimes cause mild infections such as "strep throat", or skin and soft tissue infections including impetigo and cellulitis.

More rarely, these bacteria produce a toxin that triggers a distinctive skin rash – it looks like small, raised bumps and feels rough, like sandpaper. When this happens, the illness is called scarlet fever. The rash usually starts on the chest and stomach and then spreads. Infected individuals may also develop a white coating on their tongue that peels, leaving the tongue feeling red, swollen and covered in small bumps. Scarlet fever was a common cause of death in childhood up until the 1940s, but can now be successfully treated with antibiotics.

Strep A bacteria can also occasionally get into the bloodstream or cerebrospinal fluid surrounding the brain and spinal cord, where they can trigger life-threatening infections such as necrotising fasciitis ("flesh-eating disease") or streptococcal toxic shock syndrome, where bacterial toxins trigger an uncontrolled and excessive immune reaction. This is known as invasive group A strep (iGAS) disease.

How problematic is strep A?

Globally, strep A ranks among the deadliest pathogens on Earth. In high-income countries, strep throat – a common cause of sore throats, particularly in children and teenagers – is usually treated with antibiotics. However, in countries where access to medical care is limited, untreated or repeated strep A infections can spark a condition called acute rheumatic fever, where an overactive immune response to the bacterium triggers inflammation and scarring of the heart's valves. Subsequent strep A infections can trigger further episodes, eventually leading to rheumatic heart disease, which claims around 300,000 lives each year. IGAS is responsible for a further 150,000 deaths per year.

Strep A infections can occur any time of year, but outbreaks of strep throat and scarlet fever tend to be more common during the winter and spring. This year, that pattern appears to have been somewhat disrupted: France, Ireland, the Netherlands, Sweden, and the UK have reported an increase in iGAS and scarlet fever cases throughout 2022, although this has been particularly marked during the second half of the year.

Why are these infections occurring now?

Many of the countries that are currently reporting increases in iGAS and scarlet fever have also been experiencing unusually early waves of influenza and respiratory syncytial virus (RSV) during 2022, while COVID-19 continues to circulate. Such infections can alter the balance of immune cells and bacterial flora in the body, potentially enabling Strep A bacteria to colonise places they don't usually go. Strep A infections are also more likely following chicken pox – another viral infection.

In its latest update on the situation, the World Health Organization (WHO) said: "the observed increase may reflect an early start to the GAS infection season coinciding with an increase in the circulation of respiratory viruses and possible viral coinfection which may increase the risk of invasive GAS disease. This is in the context of increased population mixing following a period of reduced circulation of GAS during the COVID-19 pandemic."

Another possibility is that decreased exposure to strep A infections during the COVID-19 pandemic has slowed the natural build-up of immunity levels in children, resulting in a greater number of susceptible individuals.

How worried should I be?

Transmission of strep A occurs during close contact with an infected person, and spreads through coughs, sneezes, or contact with a wound. Regular hand-washing, using disposable tissues to catch coughs and sneezes, wearing a face mask, and keeping away from others if you feel unwell, can all help to reduce the risk of transmission. Good indoor ventilation can also help to reduce transmission of strep A, not to mention the numerous respiratory viruses that are currently circulating. However, the vast majority of step A infections are mild, and many of us harmlessly carry the bacteria without it ever causing any problems.

Despite a moderate increase in iGAS-related infections and deaths in some countries, the WHO currently assesses the risk for the general population as "low". There is nothing to suggest the bacterium has changed in any significant way or become more resistant to antibiotics in recent months.

Even so, WHO Regional Director for Europe Dr Hans Henri P Kluge called on countries to "increase vigilance to iGAS cases, especially when respiratory viruses are widely circulating in children".

Vaccination against seasonal influenza and COVID-19 should also be promoted, the WHO said.

Because iGAS cases can be managed easily if they are detected early enough, parents should also be aware of potential warning signs and when to consult a doctor.

Warning signs

Sore throats and headaches are common during the winter months, but if a child also develops a fever, nausea or vomiting, or fine pink-red rash that feels like sandpaper, it may be a sign of scarlet fever, and you should consult a medical professional for advice. Although scarlet fever can be serious, it is usually a mild illness and most children will recover without complications – especially if they receive proper treatment with antibiotics.

IGAS infections often start out with non-specific symptoms such as fever, tiredness, loss of appetite, but can rapidly progress to severe illness. Parents should be aware of potential symptoms of necrotising fasciitis and streptococcal toxic shock syndrome, and seek medical attention if their child seems unwell and also develops severe muscle aches, localised muscle tenderness, redness at the site of a wound, a faster than normal heart rate, or rapid breathing.