What is Strep A, the common bacterium that has killed 6 children in the U.K.?

Group A Streptococcus infections are rising in the U.K. (CNN-CDC)

Health officials in the United Kingdom are advising parents and schools to watch for Strep A infections following the recent deaths of six children.

With COVID-19 restrictions such as masking and social distancing no longer required in the U.K., infections such as Strep A are spreading more easily, with cases increasing over the past month.

Also known as Group A Streptococcus (GAS), Strep A can cause a range of symptoms varying from minor to severe but is not fatal for most people who become infected.

Doesn't always cause symptoms

Strep A is a bacterium found in the throat and on the skin. It usually causes fever and throat infections, and many people carry it without any symptoms. However, they can still spread it to others through coughs, sneezes and close contact.

Symptoms of infection include pain when swallowing, fever, skin rashes and swollen tonsils and glands, with infection common in crowded settings such as schools and daycare centers, the U.S. Centers for Disease Control and Prevention (CDC) says on its website.

"(Infection) tends to be fairly harmless," Beate Kampmann, professor of Paediatric Infection & Immunity, and director of the Vaccine Centre at the London School of Hygiene & Tropical Medicine, said in a statement on Friday.

"(But) in very rare circumstances when the bacterium produces a toxin it can gain access to the bloodstream and cause really serious illness" such as sepsis, heart inflammation and toxic shock with organ failure, she said.

She advised parents to seek medical advice immediately if a child looks "very ill" with symptoms such as fever, vomiting, muscle aches or a rash.

To confirm a Strep A infection, clinicians usually either use a rapid antigen detection test (RADT) or a throat culture, according to the CDC. A culture is when a sample such as mucus or skin is taken from a person and tested to see if it contains a bacterial infection, like Strep A. Due to the varying sensitivities of RADTs, a throat culture is the preferred diagnostic test.

Similarly in the UK, infections are typically diagnosed with a culture taken from the infected site -- for example, the throat, according to the U.K. Health Security Agency (UKHSA).

Usually treatable with antibiotics

Invasive Group A Streptococcus (iGAS) is the term used when the bacteria invade the body, overcoming its natural defenses to enter areas such as the blood, and is more dangerous, the UKHSA explains on its website.

While there is no vaccine to prevent Strep A or iGAS infections, antibiotics are usually effective at treating them.

"We are seeing a higher number of cases of Group A strep this year than usual," Colin Brown, deputy director at UKHSA, said in a statement on Friday.

The increase in iGAS this year has particularly been observed in children under 10, the UKHSA added. Five children have died in England. One death has been reported in Wales, according to Public Health Wales.

Data from UKHSA shows that there were 2.3 cases per 100,000 children aged 1 to 4 between mid-September and mid-November, compared with the average of 0.5 in the pre-pandemic seasons (2017 to 2019).

For children aged 5 to 9, there were 1.1 cases per 100,000, compared with the pre-pandemic average of 0.3.

The last period of high infections was between 2017 to 2018, with four children under 10 dying in the equivalent period, the statement added.

The UKHSA said it doesn't believe a new strain is circulating, with the increase in infections likely a result of "circulating bacteria and social mixing."