<prompt> Sentinel laboratories are mainly involved in:External Quality Assessment of laboratoriesDiagnosis of HIV infectionControl of BioterrorismDiagnosis of Tuberculosis  <response>: Because communication between clinical and public health laboratories is so critical in the post-2001 era, Centre for Disease Control CDC created an organizational structure whereby isolates and lines of communication flow freely among numbers. The Laboratory Response Network LRN was originally designed as a four-tier system. Clinical laboratories Level A were at the bottom of a triangle, sending specimens to a public health laboratory level B or Level C state public health laboratory for confirmation. Isolates were ultimately sent to CDC or United States Army Medical Research Institute for Infectious Diseases USMRIID-Level D, for archiving ang sophisticated molecular testing. This original system has now been changed to a three-tier system in which Level A laboratories are now called Sentinel laboratories; Level B C laboratories are called Reference laboratories Level D are called National laboratories. The main role of Sentinel Microbiology laboratories is to raise suspicion when a targeted agent is suspected in a human specimen. Detection of a possible bioterrorism event will depend on: A laboratory having an active microbial surveillance and monitoring program Vigilant technologists looking for a disease that does not occur naturally in a paicular geographic region eg: Plague in New York city; is transmitted by an aerosol route of infection; is a single case of disease caused by an unusual agent eg: Burkholderia mallei usually only seen in the far east; Good communication with infection control practitioners, infectious disease Physicians and local or regional public health laboratories. Ref: Bailey Scotts Diagnostic Microbiology; 12th edition; Page: 954-955 