While tetanus is caused by a single strain of bacteria, S pnemoniae seeks to evade the human immune system by coating itself in 90 variations of sugar capsule that mimic human cell coatings. Seven of these capsule variations, the most common in children and adults, were included in the 2000 version of Prevnar to create immunity against them. The 19A strain is named after its sugar capsule type, which is not among the seven in Prevnar. With the most common seven strains knocked down by Prevnar, the next several most common, including 19A, filled the vacuum. Physicians in the US then barraged kids with antibiotics, often unnecessarily, Pichichero said. That created evolutionary pressure in favor of the bacteria most able to resist antibiotics.
The 19A strain, for example, has developed resistance to every antibiotic approved by the FDA for use in children with ear infections (18 antibiotics). Having anticipated this problem, Wyeth began working on a vaccine that would also protect against the next six most common strains of S. pnemoniae, including 19A, almost as soon as it got approval for the original vaccine. Even if all goes well, however, the 13-strain vaccine is not expected before 2010.
In the current study, two pediatricians used tympanocentisis to identify S pneumoniae strains that caused ear infections in children between September 2003 and June 2005. All the children had received the Prevnar vaccine. Among 1815 children, aged 6 to 36 months, in whom otitis media was diagnosed, tympanocentesis was performed in 212, yielding 59 cases of S pneumoniae infection and 9 cases infected with a serotype 19A strain resistant to all FDA-approved antibiotics for use in children.
|Contact: Greg Williams|
University of Rochester Medical Center