[1] Michael E DeBakey VA Med Ctr, VA Hlth Serv Res & Dev Houston Ctr Excellence, Houston, TX USA
[2] Baylor Coll Med, Dept Med, Infect Dis Sect, Houston, TX 77030 USA
[3] Univ Texas Hlth Sci Ctr San Antonio, Dept Med Infect Dis, San Antonio, TX 78229 USA
[4] S Texas Vet Hlth Care Syst, San Antonio, TX USA
[5] Baylor Coll Med, Dept Med, Sect Geriatr, Houston, TX 77030 USA
[6] Baylor Coll Med, Dept Mol Virol & Microbiol, Houston, TX 77030 USA