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Streptococcus: What it is and why chickenpox raises risk

01/27/2015 05:00 EST | Updated 03/29/2015 05:59 EDT
Toronto health officials blamed an infection from "a common bacteria" known as Group A streptococcus (GAS) this week in the death of a three-year-old boy who attended an east-end daycare.

The child was reportedly running a fever on Jan. 13. His parents took him home and he died four days later.

While GAS is often carried on the skin and in the nose and throat in many people, it is generally not regarded as dangerous for most of the population.

Immunologists and microbiology experts explained how the bacteria spreads, who’s most at risk, and how chickenpox may be a danger factor.

What is Group A streptococcus?

Streptococci are bacteria that commonly cause infections. Among the most common infections in pediatrics is streptococcus pneumonia or impetigo, a contagious skin infection.

There are eight strains of the bacteria, classified from groups A through H. Different types of streptococci cause different types of infections. A common, mild illness brought on by the human-specific Group A streptococcus is strep throat. GAS can also cause more serious infections such as pneumonia, bloodstream infections and infections to the brain.

"It’s also associated with diseases that are part of your immunogenic response to infection, such as rheumatic fever and a condition called glomerulonephritis, or inflammation of the kidneys," said Dr. Allison McGeer, director of infection control at Mount Sinai Hospital.

How common is this bacteria?

Very common, according Dr. Rita Shahin, an associate medical officer of health with Toronto Public Health.

"A lot of people carry it either on their skin or in their throat," Shahin said, noting that it’s only in rare cases that it becomes invasive, entering "sterile" body sites such as the bloodstream or the lining of the brain.

"We don’t know why in certain people that happens, and we do know that in a small percentage of those people who get invasive disease, they can go on to die of this disease," she said.

McGeer said about one in 10 children carries Group A strep in the throat without symptoms, and in the overall population, about two in every 100,000 people will develop any type of serious infection.

Toronto Public Health estimates there were 150 cases of Group A streptococcus in Toronto last year, occurring more often in the winter than summer. About 15 per cent of people who develop invasive disease will die, she said.

When does it become dangerous?

An invasive streptococcal disease is one that has been isolated from a part of the body that is normally sterile, said Dr. John McCormick, an associate professor of microbiology with Western University.

"So not your throat or skin, but more so a blood sample or a soft-tissue infection, those types of areas," he said.

Bacteria can make its way into deep muscle tissue and the lungs, for example.

When this happens, one common form of invasive GAS disease is necrotizing fasciitis, also known as flesh-eating disease.

Added danger may also come in the form of streptococcal toxic shock syndrome, a disease that arises when the immune system "overreacts," McCormick said.

"A patient’s blood pressure really drops, you can get organ failure and other things," he said, adding that the mortality rate in children is about 50 per cent if they develop the condition.

Early treatment with antibiotics can reduce the risk of death in cases of invasive illness.

How are Group A streptococci transmitted?

The bacteria spreads by direct contact, for example skin on skin or respiratory droplets.

Although Toronto Public Health officials have said the Toronto daycare has been disinfected, McGeer said environment is typically not the issue.
 
"It's important for people to remember that it's very uncommon for serious illness to occur in a second child in this setting," she said.

"Generally speaking, if there's not a case in the next two weeks, there's not going to be another one."

Family members living in a close setting or sharing beds could be at higher risk of transmission.

"If somebody in a household gets sick with Group A strep, there's about a 10 per cent chance that another member of the household will have Group A strep – not the infection, just colonization," McGeer said. "The risk they’ll get an infection is much, much lower."

Shahin added that if parents of children who attended the Toronto daycare notice symptoms such as sore throat or fever, "or if their children develop symptoms like that beyond a mild cold," they should take them to the doctor, who can conduct a throat swab test.

Who is most at risk?

It’s tough to say, according to McGeer.

"People who die from this infection often have perfectly normal immune systems," she said. "We still don’t know why an occasional person can develop a catastrophic illness with Group A strep while most other people don’t."

Children are more likely to carry a strain of almost any bacteria, McGeer said.

While handwashing is always good practice to prevent the spread of bacteria, McCormick also points to a research paper co-authored by McGeer that found chickenpox to be a factor in invasive Group A strep.

"Any disease that damages your skin and leaves you with open lesions on skin can increase your infection," McGeer said.

For that reason, health officials recommend that children get vaccinated against chickenpox.

For more information, you can visit Toronto Public Health’s invasive GAS fact sheet or consult your doctor.

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