Biostat Chips Gone Bad

Colonists are run through their final medical exam and given a does of antibiotics. Inside are tiny nanites that use material ingested (dirt and stuff) to assemble a chip that attaches to the cordial stem and builds neronets through the brain.  These chips are used to monitor the populations health. 

Now, colonists are dieing. The chips are malfunctioning causing blackouts, disorientation and sometimes death.