Polycocyx astris was a form of space-dwelling microbe that resided in interstellar dust.

While answering questions sent from Miss Malvin's fourth grade class at Worley Elementary School in Kenmare, County Kerry, Ireland, Doctor Phlox recalled the Polycocyx astris as a particularly virulent species. They had been known to lie dormant for millions of years before infecting a host and causing a 'nasty cold'. (ENT: "Breaking the Ice")