USAMRIID (pronounced you-sam-rid) stands for the United States Army Medical Research Institute for Infectious Diseases.
Based at Fort Detrick in Frederick, Maryland, the facilities of USAMRIID are used primarily for research on counter measurements for biological warfare. Along with the next-door National Biodefense Analysis and Countermeasures Center (NBACC) and the nearby United States Army Medical Research Institute of Chemical Defense (USAMRICD) they handle many of the biological threats that come up in regards to national defense. When a new infectious agent or biological threat comes up they are on the case to have the data on file regarding any incident that, again, may eventually pertain to national biological defense.
USAMRIID was featured in Richard Preston's best-selling book "The Hot Zone" which described the outbreak of the then-undiscovered Ebola Reston (which was discovered in Reston, Virginia but was not discovered by Preston since people say if you take off the P in Preston you have "reston" left). The book describes the events of decontamination of medical research facilities used to store imported monkeys from the Philippines. It was then discovered that Ebola Reston can't be caught by humans but the same virus has a 90% fatality rate in primates.
I had never heard of USAMRIID before until I read Richard Preston's "The Hot Zone".