I Just Got Back From Mexico...

One third of visitors to poor countries from rich countries get sick. Experts warn tourists to avoid uncooked food, street vendors, ice, and tap water. By obeying, they lower the risk of getting sick to… one third. The truth is that no one knows how to prevent traveler’s diarrhea. Poor sanitation seems essential, but travel itself must play a role. The Swiss get sick when they visit the US.

Tourists visiting the tropics worry unnecessarily about parasites. Germs and protozoa like malaria remain a problem, but larger creatures reproduce slowly. Victims must stay long enough and undergo repeated exposure before they accumulate enough to realize something is wrong. If you harbor a few dozen schistosomes, flukes, or hookworms, you won’t notice.

Having said this, I visited one horrified guest who had seen what looked like an earthworm swimming in the toilet after a bowel movement. Unfortunately for my education, he had flushed it down. This was undoubtedly an ascarid, a parasite that affects a billion people worldwide and an unknown number in the US. Unlike parasites such as hookworms which bite into the intestine and eat your blood, ascarids swim freely and eat what you eat. You can support a dozen without difficulty. Victims get into trouble when huge numbers cause an obstruction or when a single worm crawls into a duct and gets stuck. If you return from vacation with a small infestation, you have little to worry about. The females will mate, but their eggs only hatch outside the body in warm earth, so they disappear down the sewer, and the average ascarid dies after a year or two.