Possible Clues:

• 50 per cent written in verse? It makes one sick!
• Rash causing a lot of disease
• Flu outbreak, e.g.
• Many cases where I'm in a piece of them
• Death reduced by a third in large-scale outbreak
• Disease got by daughter tucking into pie mice fouled up
• ''The Andromeda Strain'' fear
• Spreading disease of huge proportions, half caught
• Lots of cases make half a hundred at last
• 50% taken by Great Plague