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Number and cumulative percentage of meningococcal meningitis from PCR confirmation with ctrA gene by age group among children aged < 5 years old in China, South Korea, and Vietnam by age group, 1999 through 2002a.a Surveillance periods: January 1, 2000-December 31, 2002, China; September 1, 1999-December 31, 2001 (4-month hiatus, August to November 2000), Korea; March 4, 2000-March 3, 2002, Vietnam.
