1. Public Health Institute, Oakland, California, USA
2. Department of Epidemiology, University of Michigan, Ann Arbor, Michigan, USA
3. Instituto de Microbiologia, Colegio de Ciencias Biologicas y Ambientales, Universidad San Francisco de Quito, Quito, Ecuador
4. Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, Michigan, USA
5. Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
6. Department of Veterinary and Biomedical Sciences, University of Minnesota, St. Paul, Minnesota, USA