Health officials in Britain said several children had recently died after being diagnosed with invasive Group A streptococcus, sounding the alarm for schools and prompting parents to spring to action.

“We are seeing a higher number of cases of Group A strep this year than usual,” Dr. Colin Brown, the deputy director of the U.K. Health Security Agency, said in a news release on Friday. While the bacteria usually causes mild infections, he said, in rare circumstances it can cause more serious illnesses.

He urged parents to be vigilant of symptoms and to seek medical attention as quickly as possible if their child began showing signs of deteriorating health.

Jim McManus, president of the Association of Directors of Public Health in Britain, expressed similar concerns to the BBC, telling the network that the number of severe cases would rise.

“We seem to have forgotten that strep A is around,” he said. “In some cases perhaps we had thought this had gone away because we had been thinking about other infections.”

Here’s a breakdown of what we know.

What is Group A streptococcus?

Group A streptococcus is a common bacteria that can be found in the throat or on the skin, according to the U.K. Health Security Agency. The bacteria doesn’t always cause illness, but it can cause tonsillitis, sore throat, skin rashes, scarlet fever and impetigo.

In older adults, very young children or immunocompromised people, the bacteria can also sometimes get into the bloodstream and cause a more serious illness known as invasive Group A streptococcus, or iGAS.

Necrotizing fasciitis, necrotizing pneumonia and streptococcal toxic shock syndrome are some of the infections caused by iGAS. They are frequently fatal.

Is it contagious?

Yes. Group A streptococcus is highly contagious and spreads through close contact with an infected person. It could be passed through a few different ways, including coughs, sneezes or by contact with a wound, health officials said.

Even if a person isn’t feeling sick or showing symptoms of infection, the bacteria can be passed on. The risk of spread is greater, however, when a person is visibly unwell.

Officials note that infections rarely become serious and that, when treated with antibiotics, a patient with a mild illness stops being contagious about 24 hours after starting medication.

What are the symptoms?

Symptoms can include sore throat, fever, chills, headache, muscle aches and a rash.

How serious is the situation?

As of Tuesday, seven children in England had died after being diagnosed with invasive Group A streptococcus, a U.K. Health Security Agency spokesman said. Additional deaths have been reported in Northern Ireland and Wales.

Government officials have said there has been an increase in invasive Group A strep cases this year, mostly in children under 10. So far this year, there have been 2.3 cases per 100,000 children 1 to 4 years old. Between 2017 and 2019 there were an average of 0.5 cases in that age group. The next age group older has seen a similar increase in cases: 1.1 per 100,000 children between 5 and 9 this year, compared with 0.3 from 2017 to 2019.

In the 2017 to 2018 winter season, four children in England under 10 died.

Why are cases rising now?

It is unclear. Health officials have said that there is no evidence that a new strain is circulating but that the increase in infections is most likely related to high amounts of circulating bacteria.

Doctors said a combination of factors, including more social mixing compared with previous years and a rise in other respiratory viruses, may be contributing.

I’m a parent. What can I do?

Trust your own judgment, health officials said. You may want to contact a doctor for a number of reasons, including if your child is getting worse, if you observe your child eating less than normal, if you notice signs of dehydration or if your child is feeling very tired.

Parents may want to call emergency services if they notice their child having difficulty breathing or observe pauses in a child’s breathing.

Also, do not underestimate the importance of good hand and respiratory hygiene — washing hands with soap and warm water for 20 seconds and using tissues to cover coughs and sneezes — to help stop the spread of viruses.