Q: When Halley's Comet reappeared in 1969, that winter a flu epidemic killed more than 60,000 people in Britain. In 2008 Comet Nostradamus (and others) passed by, and now we face a flu pandemic. Is this mere coincidence, or were the ancients right to fear comets as bad omens and bringers of pestilence? What other natural disasters have been attributed to comets?
An interesting question, and one which is wrong on almost every level. The question's author may be referring to the theory of panspermia, where micro-organisms or disease can be brought to Earth by comets. Unfortunately the question gets pretty much everything else wrong.
Halley's comet did not appear in 1969. It was around in 1910 and again in 1986. I can't find any record of a Comet Nostradamus. There is a bright comet every few years - they aren't that rare so claiming co-incidence doesn't really make sense. Also the Earth passes through comet dust several times per year. The major meteor showers are associated with dust and debris from comets. If comets were all full of germs and pestilence, then there would be major outbreaks several times per year.
At least the questioner didn't claim the world was going to end in 2012.