ACKNOWLEDGEMENTS
We thank Bob Gilmore, Kevin Brandt and Brittany Armstrong for thoughtful
and critical reading of the manuscript. We thank Jean-Marc Lanchy, James
Kovaks and Crystal Vander Zanden for useful discussions. We thank Robert
Landick for the RL211 strain. We thank Irina Goodrich for excellent
technical support. The findings and conclusions in this report are those
of the authors and do not represent the official position of the Centers
for Disease Control and Prevention.