In our tests, we thought the length of the flight, or the country in which it originated, might affect the results. It didn't. While our lab turned up 750 colonies per milliliter during a Chicago-Mexico City flight, we found millions of colonies on that short hop to St. Louis. Among our other findings: Salmonella, a well-known bacterium that can cause violent illness, on a Continental flight to Newark, N.J. Then there were the eggs: On a United flight, our lab found aquatic insect eggs that, after a few days, hatched into maggots. "I've never seen it in all the 26 years I have been testing water," Dr. Hendrickson says.