Communists Allege US Use of Germ Warfare, 1951, Feb. 22 1952

These claims have been confirmed and disconfirmed by various parties since 1951.  The most recent (and generally accepted claim is a 1998 disconfirmation by two historians at the Woodrow Wilson Center's Cold War International History Project who, supplying a cache of Chinese and Soviet documents, show that the allegations were an elaborate disinformation campaign.  The Soviets ended the campaign a year after Stalin's death.

In 1951 the claims were vague.  In early 1952, after a smallpox outbreak and several dozen soldiers contracting cholera and plague, China and North Korea suspected America.  Feb. 22 1952 the North Korean Foreign Ministry made formal allegations that US planes had dropped infected insects onto North Korea.  IRC and WHO found no evidence, and China arranged a further investigation by the World Peace Council (originated in 1950 from the Soviet Union's Cominform), which confirmed the allegations.