My guess is that you were already coming down with something, but not having symptoms yet
(and it's easy to attribute minor things like poor sleep or sluggishness to taper, anyway
), and then actually noticed it the day after the race. Plus it's possible, if travel to the race or time in crowded public places
(packet pickup?
) was involved, that you got exposed to a cold/flu bug at that time, and it takes a couple of days for symptoms to appear after that. .That a race happened to come in between may have been coincidental, or it may have been one of several stressors
(along with change of routine during taper, limited sleep before the race, etc.
) that might have lowered your immunity enough to get sick. There is some evidence that long races, like IM or marathons, can lead temporarily lower immunity, but I don't know if any Oly falls in that range or not. Timewise, maybe, in terms of stress on the body, not sure.
One other possibility, if symptoms are only sore throat, body aches, and/or GI issues, dirty water? I've had similar symptoms after some of my races here in Vietnam--the giveaway is when other people who did the same race, or friends/family who just went swimming, have the same issues.