A Cruise
The Bug: Norovirus, a contagious virus that causes vomiting and diarrhea. It recently infected passengers on the QE2.

Your Best: Defense Washing hands (or using a 60 to 70% alcohol hand sanitizer) several times a day will kill germs acquired from contaminated surfaces like doorknobs. Before booking, check out the Vessel Sanitation Program at cdc.gov/travel for cleanliness reports for major cruise lines.

A Hotel
The Bug: Bedbugs. Last year's infestation at London's Mandarin Oriental hotel proves that these irritating pests like posh establishments, too.

Your Best: Defense Peel back sheets and examine the mattress, headboard, and box spring. Bedbugs are hitchhikers, so if your hotel has been infested, don't bring luggage into your home; get bags professionally fumigated first, and wash or dry-clean clothes.

Overseas
The Bug: Tetanus, a bacteria that can contaminate a wound and cause a potentially fatal disease. A vaccine can save you if given beforehand or shortly after exposure, but it may not be as readily available as it is in the United States.

Your Best: Defense Everyone should get a tetanus booster every 10 years. If you can't remember your last shot, you're safe (and better off) revaccinating in the United States 4 to 6 weeks before a trip.