1. Clinical Microbiology Laboratory, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 191041;
2. Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, Michigan 481092;
3. Department of Community and Preventive Medicine, MCP Hahnemann University, Philadelphia, Pennsylvania 191293; and
4. Laboratorium voor Microbiologie, Universiteit Gent, Ghent, Belgium4