1. Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
2. Mycoplasma Laboratory, Statens Serum Institut, DK-2300 Copenhagen, Denmark
3. Department of Public Health, Temple University, Philadelphia, PA 19122, USA
4. Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
5. The University of Texas School of Public Health, Houston, TX 77225, USA