By the end of November, more than thirty men of the 13th had been discharged since the Battle of Leesburg/Ball’s Bluff for chronic illnesses and a few more for wounds that would not heal, according to their muster rolls in McLean’s history.
Pvt. James Martin Lewis of the Alamutcha Infantry is representative. McLean: “Discharged for disability ‘on account of great constitutional disability caused by results of typhoid fever.’ November 20, 1861, from Leesburg, 5′ 10″, dark complexion, gray eyes, sandy hair.”
On Dec. 1, an additional thirty-six were listed as ill.
13TH MISSISSIPPI INFANTRY REGIMENT 
That’s my ancestor (Pvt. James Martin Lewis of the Alamutcha Infantry) and he recovered enough from typhoid to reenlist for the Atlanta campaign with 8th Miss Regt.
Cool. Thanks for the comment and the information, Richard.