Possible Clues:

• That's the sole thing to make one sick
• Strange seaside condition
• 'Well, that won't make Sidney come back with comfort (7)'
• 'Make it to the seaside? Well, never with this (7)'
• Seaside (anag.)
• Illness, malady
• Peculiar seaside complaint
• Pathologist's study
• 'See, said to be not as well (7)'
• Complaint from Germany is moderate