This is a fascinating statement if we look back at a diary entry on 14 June 1965 in which Clark described the different branches that comprised the Transportation Division of MACV J-4:
If Clark's diary is correct, MACV disciplined Captain Heizman for contracting a sexually transmitted disease by reducing him to non-commissioned officer status and transferring him from Staff Branch to Movements Branch. Under Article 15 of the Uniform Code of Military Justice, General Westmoreland possessed the authority to administer non-judicial punishment for minor offenses. Clark wrote in his diary on 12 June 1965, "The VD rate is quite high here, approximately 10% of all officers and EM contract VD within 2 months of arriving in the country. Names of officers infected are reported to General Westmoreland thru channels from the medics."
Sexually transmitted diseases (STDs) were a serious problem for MACV. In 1965, STDs accounted for 280 out of every 1,000 hospital or quarters admissions among U.S. troops in South Vietnam and was the single most prevalent reason for a clinic or hospital visit by a U.S. serviceman. In comparison, battle wounds accounted for only 61 out of every 1,000 hospital or quarters admissions. 
 Medical Support, 1965-1970. Department of the Army, 1973. Chapter II - "Health of the Command."