North America: Canada, Saint Pierre and Miquelon, and the United States extend from the Arctic to the subtropical cays of the southern United States.
In 1994, an international commission certified the eradication of endemic wild poliovirus from the Americas. While ongoing surveillance in formerly endemic Central and South American countries confirms that wild poliovirus transmission remains interrupted, an outbreak of vaccine-derived type 1 poliovirus occurred in the Dominican Republic and Haiti in 2000.
The incidence of communicable diseases is such that they are unlikely to prove a hazard for international travelers greater than that found in their own country. There are, of course, health risks, but, in general, the precautions are minimal. Certain diseases occasionally occur, such as plague, rabies in wildlife (including bats), Rocky Mountain spotted fever, tularemia, arthropod-borne encephalitis, and seasonal outbreaks of influenza. In addition, outbreaks of influenza have occurred during the summer in Alaska and Northwestern Canada on cruise ships and during the overland segments of those excursions. Rodent-borne hantavirus has been identified, predominantly in the western states of the United States and in the southwestern provinces of Canada. Giardia infections can occur among campers and those who drink water from fresh water lakes, streams and rivers.
In 2002, in the United States, West Nile Virus (WNV) activity was reported from 44 states and the District of Columbia (DC), compared with 27 states and DC in 2001, and WNV was detected for the first time in 16 states. Lyme disease is endemic in the northeastern, mid-Atlantic, and midwestern United States. Occasional cases have been reported from the Pacific Northwest. During recent years, the incidence of certain food-borne diseases (e.g., salmonellosis) has increased in some regions. Other hazards include poisonous snakes, poison ivy, and poison oak. In the north, a serious hazard is the very low temperature in the winter.
In the United States, proof of immunization against diphtheria, measles, poliomyelitis, and rubella is now universally required for entry into school. In addition, the school entry requirements of most states include immunization against tetanus (49 states), pertussis (44 states), mumps (46 states), and hepatitis B (29 states). Some states now require varicella or hepatitis A vaccination for school entry; however, state requirements differ widely.