By Maggie Fox, Health and Science Editor

WASHINGTON, Oct 18 (Reuters) - A new strain of bacteria is emerging as a major cause of childhood infections but even drug-resistant versions of the bug can be killed off with the right antibiotics, doctors said on Thursday.

Doctors and parents should be aware of it, however, and switch antibiotics for children with severe infections who do not respond quickly to standard therapy.

The bacteria is a type of Streptococcus pneumonia that is not one of the seven strains covered in a routine childhood vaccine, a team at Boston University and the Massachusetts health department reported.

"I think clinicians should be aware that the vaccine, as effective as it is, still leaves children at risk for invasive pneumococcal disease," Dr. Stephen Pelton, chief of pediatric infectious disease at Boston University, said in a telephone interview.

Wyeth's <WYE.N> Prevnar, given routinely to young children, protects against seven strains of S. pneumoniae, known commonly as pneumococcal bacteria. These germs cause ear infections, meningitis, pneumonia and blood infections.

The vaccine has greatly reduced the number of infections among not only children but older adults. Pelton said Massachusetts had seen a 75 percent reduction in the number of severe pneumococcal cases since 2000.

Wyeth and government agencies gave the Massachusetts team funding to look to see what other strains of bacteria were now stepping into the void.

They found the 19A strain was becoming more common. "It causes about 40 percent of pneumococcal infections in children under the age of 18 in Massachusetts," Pelton said. He said the percentage was similar across the United States.

In 2001-2002, just 10 percent of cases were caused by the 19A strain.

The strain resists penicillin and in many cases also amoxicillin, Pelton's team reports in this week's issue of the U.S. Centers for Disease Control and Prevention's report on death and disease.

And 15 percent were resistant to another antibiotic called ceftriaxone.

This week several reports have pointed to increasing numbers of infections with drug-resistant "superbugs," including a report in the Journal of the American Medical Association that estimated methicillin-resistant Staph aureus, or MRSA, killed 19,000 people in 2005 and made 94,000 seriously ill.

An MRSA outbreak that killed one 17-year-old caused 21 Virginia schools to close this week.

For the drug-resistant strains of S. pneumoniae, Pelton said the antibiotic vancomycin will work, or combination therapy with vancomycin and cefotaxime or ceftriaxone.

Healthy children are not considered at serious risk from the infection but Pelton said children with sickle cell disease, HIV infection, lung disease, diabetes or kidney disease need special attention.

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