The United States requires no vaccinations for entry from most countries. The Centers for Disease Control and Prevention recommends ensuring routine vaccinations remain current before any international travel, including measles-mumps-rubella, diphtheria-tetanus-pertussis, varicella, polio, and annual influenza. Hepatitis A and hepatitis B vaccinations carry recommendations for travelers who may consume food or water outside major metropolitan areas or engage in activities with potential exposure to bodily fluids. Rabies vaccination receives consideration for those planning extended time in wilderness areas where contact with bats, raccoons, skunks, or foxes becomes possible. Decisions on all vaccinations belong solely to travelers and their licensed healthcare providers.
Healthcare infrastructure in the United States operates almost entirely on a private fee-for-service basis. No universal government healthcare system exists for residents or visitors. Medical care costs rank among the highest globally in absolute terms. An emergency room visit for a moderate injury without admission generates bills between $1,500 and $3,000 before any procedures or imaging. A single night of hospital admission averages $5,000 to $10,000 before physician fees, tests, or treatments. Ambulance transport costs range from $400 to $2,000 depending on distance and level of care during transport. Prescription medications purchased at retail pharmacies cost significantly more than in most other developed nations. The healthcare system assumes all patients can demonstrate ability to pay or possess insurance before non-emergency treatment begins.
Travel medical insurance specifically covering the United States becomes essential rather than optional. Standard health insurance policies from outside the United States generally provide no coverage within the country. Visitors requiring medical care without insurance face immediate payment demands or denial of service outside true emergency situations. Emergency rooms must provide stabilizing care under federal law regardless of ability to pay, but stabilizing care means only the minimum treatment necessary to prevent death or serious deterioration, not comprehensive treatment or follow-up care. Policies should cover emergency medical treatment, hospital admission, medical evacuation, and repatriation. Minimum recommended coverage amounts begin at $100,000 for medical expenses and $50,000 for emergency evacuation, though higher limits reduce financial exposure given typical costs. Some policies exclude pre-existing conditions entirely; others cover them with waiting periods or additional premiums.
Prescription medications brought from outside the United States must remain in original labeled containers with prescribing physician information visible. Customs and Border Protection permits personal-use quantities, generally defined as a 90-day supply for each medication. Controlled substances including opioid pain medications, benzodiazepines, amphetamines, and some sleep aids require additional documentation including the original prescription and potentially a letter from the prescribing physician explaining medical necessity. Cannabis products remain federally illegal despite legalization in certain states for medical or recreational use, creating potential criminal liability for possession during any interstate travel or in federal jurisdictions including national parks and airports. Federal law supersedes state law in all federal jurisdictions. Travelers requiring specific medications during their stay should verify those medications carry approval from the Food and Drug Administration and remain legal at the federal level.
Altitude sickness occurs in mountain regions above 8,000 feet elevation. Denver sits at 5,280 feet and rarely causes altitude symptoms in healthy individuals, though reduced exercise capacity affects some visitors. Rocky Mountain National Park reaches elevations above 12,000 feet on Trail Ridge Road. Pikes Peak summit stands at 14,115 feet. Mount Rainier reaches 14,411 feet. Denali in Alaska rises to 20,310 feet. Symptoms of acute mountain sickness include headache, nausea, fatigue, dizziness, and difficulty sleeping. Onset typically occurs 6 to 12 hours after arrival at altitude. Gradual ascent reduces incidence, with recommendations to sleep no more than 1,000 feet higher each night once above 10,000 feet. Descending to lower elevation relieves symptoms in all cases. High-altitude cerebral edema and high-altitude pulmonary edema represent life-threatening progressions requiring immediate descent and emergency medical care. Travelers planning activities above 10,000 feet should consult physicians familiar with altitude illness regarding prevention approaches.
Tick-borne diseases occur throughout the United States with varying geographic concentration. Lyme disease from black-legged ticks concentrates in northeastern states, upper midwestern states including Wisconsin and Minnesota, and northern California coastal areas. The CDC reports approximately 30,000 confirmed and probable cases annually with actual infections estimated at 476,000 per year based on insurance claims data. Rocky Mountain spotted fever from dog ticks occurs most frequently in North Carolina, Tennessee, Missouri, Arkansas, and Oklahoma despite the name suggesting western states. Anaplasmosis and babesiosis share similar geographic distribution with Lyme disease in northeastern and upper midwestern states. Powassan virus remains rare but carries severe neurological consequences, with approximately 25 cases reported annually concentrated in the Great Lakes region and Northeast. Alpha-gal syndrome resulting from lone star tick bites causes delayed allergic reactions to mammalian meat and occurs primarily in southeastern, mid-Atlantic, and south-central states. Prevention depends entirely on avoiding tick attachment through protective clothing, permethrin-treated fabrics, and DEET-based repellents on exposed skin.
Mosquito-borne diseases circulate at low levels. West Nile virus causes the majority of domestically acquired mosquito-borne illness, with 2,400 cases reported in 2021 and cases occurring in all lower 48 states. Severe neurological disease develops in approximately 1 in 150 infected persons, primarily those over 60 years old or with compromised immune systems. Dengue fever transmission occurs in southern Florida, southern Texas along the Gulf Coast, and Hawaii, with most years recording fewer than 100 locally acquired cases. Eastern equine encephalitis occurs in Atlantic and Gulf Coast states with typically fewer than 10 human cases annually but carries a 30 percent fatality rate when infection occurs. St. Louis encephalitis and La Crosse encephalitis remain geographically limited and rare. Mosquito exposure peaks during dawn and dusk hours in warm months from May through October in most regions, extending year-round in southern Florida, southern Texas, and Hawaii. EPA-registered insect repellents containing DEET, picaridin, IR3535, or oil of lemon eucalyptus reduce mosquito bites when applied to exposed skin.
Venomous snakes inhabit every state except Alaska, Hawaii, and Maine. Rattlesnakes account for the majority of venomous snakebites and occur in all regions including deserts, mountains, forests, and grasslands. Copperheads concentrate in eastern and central states from Massachusetts to Nebraska and south to Texas. Cottonmouths inhabit wetlands and water bodies in southeastern states from Virginia to eastern Texas. Coral snakes occur in southern states from North Carolina through Florida and west to eastern Texas, plus Arizona coral snakes in that state. The United States records approximately 7,000 to 8,000 venomous snakebites annually resulting in an average of 5 deaths per year. Most bites occur on hands and feet when individuals step near snakes or attempt to handle them. Medical treatment has improved to the point that death from snakebite becomes rare when victims reach hospitals with antivenom supplies. Antivenom administration decisions belong solely to emergency physicians based on progression of local and systemic symptoms. Avoiding snake habitat during peak activity hours at dawn and dusk, watching foot placement on trails, and never attempting to handle or photograph snakes at close range prevents the vast majority of bites.
Heat-related illness causes approximately 1,500 deaths annually in the United States according to CDC mortality data. Death Valley in California recorded a temperature of 130 degrees Fahrenheit on August 16, 2020, though the 134-degree reading from 1913 remains disputed. Phoenix regularly exceeds 110 degrees Fahrenheit from June through August, with July 2023 recording 31 consecutive days at or above 110 degrees. Las Vegas, Tucson, and Palm Springs experience similar extreme heat during summer months. Heat exhaustion symptoms include heavy sweating, weakness, nausea, headache, and dizziness. Heat stroke represents failure of the body's temperature regulation and manifests as body temperature above 104 degrees Fahrenheit, altered mental state, hot dry skin or heavy sweating, rapid pulse, and potential loss of consciousness. Heat stroke requires immediate emergency medical care as organ damage and death can occur rapidly. Prevention requires consuming significantly more water than thirst indicates, typically one liter per hour during outdoor activity in extreme heat, avoiding outdoor exertion during peak heating hours between 10 a.m. and 4 p.m., wearing light-colored loose clothing, and recognizing early symptoms before they progress.