A recent Special Operation article detailed a mission when Brigadier General Crawford Sams was sent to a northern landing site to survey a North Korean village plagued with contiguous diseases. Sams concluded it was not the plague, which US soldiers were not vaccinated, but a form of smallpox, which US soldiers had been vaccinated for.
On the other hand, increasing evidents suggested the bacteriological warfare indeed took place with declassified documents linking Fort Detrick and Air Forces.
General Sams' personal report after the 'Operation Sams' was used as a rebuttal by the US at the time to the accusations made by China and North Korea. However, the simple fact that General Sams did not bring back any physical evidence, not even a blood sample seems to be a hint to the real truth.