The strain of bacteria that recently sent a Toronto child to hospital with a hard-to-treat form of meningitis has become more prevalent and more drug resistant around the globe in recent years, experts say.
And while some have questioned whether the increased threat of the Streptococcus pneumoniae serotype 19A was fuelled by the introduction of a children's vaccine to protect against pneumococcal infections, others say this bacterial bully's surge to prominence may be unrelated to vaccine use. Either way, infectious disease experts say 19Abears watching.
"19A can be a really, really bad bug. And it can get to be a very, very highly [drug]-resistant bug," says Dr. Ron Dagan, director of the pediatric infectious disease unit of Soroka University Medical Center in Beer-Sheva, Israel. "It's definitely one of the six or seven most important [pneumococcal] serotypes in childhood infections….It is becoming more important because of antibiotic resistance."
"And it's a trend worldwide— it's not only in Canada and the U.S.," he said.
The 19A serotype— one of more than 90 known strains of this type of bacteria— is not covered by the vaccine that defends children from the middle ear infections, sinusitis, pneumonia and occasionally bloodstream infections and meningitis that these common bacteria can trigger.
The vaccine, sold under the brand name Prevnar by Wyeth Pharmaceuticals, protects against the seven strains of pneumococcus that were the leading causes of illness in children before the vaccine was introduced. Rates of infections caused by those strains have plummeted in places where the vaccine is in use.
The disease-causing potential of 19A was well-known while the vaccine was being developed. But the vaccine protects against a strain known as 19F and it was thought that component might offer some defence against 19A as well.
"We were really hoping there would be some cross-coverage of 19A and there doesn't seem to be," says Dr. Allison McGeer, an infectious diseases expert at Toronto's Mount Sinai Hospital. A new pneumococcal vaccine that would protect against 13 strains of the bacteria, including 19A, is in the final stages of clinical testing.
The 19A strain packs two punches. It can cause severe disease and easily develops resistance to the antibiotics children are frequently given to combat ear infections and the like.
Some variants — like the one that caused the Toronto meningitis case or others found to have caused ear infections in Rochester, N.Y.— are resistant to multiple classes of antibiotics approved for use in children, forcing doctors to turn to drugs normally reserved for adults to clear up the infections.
Some clinicians have questioned whether the dramatic decline in illnesses caused by the Strep pneumo strains in the vaccine has created conditions that have allowed 19A to flourish. The theory is that by vanquishing the neighbourhood thugs, the vaccine has created an opening for 19A.
Others say the jury on that is still out, noting some microbes wax and wane in undefined cycles, for reasons that aren't well understood.
"There are clearly places in the world, for example in Israel and in Korea, where serotype 19A has increased either in the complete absence of vaccine— which is the case in Israel— or before vaccine was introduced and then has continued to increase very slowly after vaccine introduction," says Dr. Matthew Moore, a pneumococcal expert with the national center for immunization and respiratory diseases at the U.S. Centers for Disease Control.
19A infections on rise in Korea
In fact, Korean scientists reported at a scientific conference earlier this fall that infections caused by 19A in that country went from zero per cent in 1991-94 to eight per cent in 1995-96 — before Prevnar was brought to market. In the period from 2001-2006, 19A strains were responsible for between 20 to 26 per cent of diagnosed pneumococcal infections in Korea.
At another conference, Dagan presented data from a study looking at Jewish and Bedouin children in southern Israel, where the vaccine is not used. The two groups of children rarely interact.
The researchers found the percentage of pneumococcal infections caused by multi-drug resistant 19A bacteria spiked from 1999 to 2005 in the Bedouin children, but no corresponding rise was seen in the Jewish children.
That suggests a multi-drug resistant variant of the 19A bacteria was introduced into Bedouin population, they said.
"The point is very clear that we don't vaccinate at all and we see actually a very rapid takeover and increase of 19A otitis media in our region," Dagan says. Otitis media is the medical term for inner ear infection.
"When you see that these more and more antibiotic-resistant strains go up, you immediately understand …some clones or some strains that are resistant to antibiotics have been introduced into the community and are facilitated by antibiotic use."