[1] Univ Costa Rica, Fac Microbiol, Ctr Invest Enfermedades Trop CIET, San Jose, Costa Rica
[2] Univ North Carolina Chapel Hill, Dept Med, Ctr Gastrointestinal Biol & Dis, Chapel Hill, NC 27599 USA
[3] Univ N Carolina, Dept Med, Div Infect Dis, Chapel Hill, NC 27514 USA
[4] Univ North Carolina Chapel Hill, Dept Microbiol & Immunol, Chapel Hill, NC 27599 USA