An outbreak of H1N1 influenza ("swine flu") was reported from the United States in April 2009. The outbreak was caused by a previously unknown strain of influenza that contained a unique combination of swine, avian, and human influenza gene segments. As of June 19, a total of 17,855 cases and 44 deaths had been identified. Initial reports from Mexico, where the outbreak started, indicated a high fatality rate in previously healthy young adults and older children, raising concerns that a worldwide pandemic might occur, similar to 1918. However, subsequent data from Mexico, as well as experience from the United States and other countries, indicate the H1N1 strain from 2009 is not nearly as lethal as some people initially feared.

The World Health Organization does not recommend any travel restrictions at this time. To protect yourself from H1N1 influenza, wash your hands regularly and avoid close contact with anyone who is coughing or sneezing. Routine use of face masks is not recommended. The symptoms of H1N1 influenza include fever, cough, sore throat, body aches, headache, chills and fatigue, similar to seasonal influenza. Any traveler to the United States who develops flu-like symptoms should immediately seek medical attention. Clinicians who suspect H1N1 influenza virus infections in humans should obtain a nasopharyngeal swab from the patient, place the swab in a viral transport medium, and contact their state or local health department to facilitate transport and timely diagnosis at a state public health laboratory. Empiric treatment with Tamiflu or Relenza should be considered for suspected cases. It is not anticipated that the influenza vaccine given in the winter of 2008-2009 will be protective against the novel H1N1 virus. For further information, go to the World Health Organization and the Centers for Disease Control.

An outbreak of Salmonella typhimurium infections was reported in January 2009, probably related to contaminated peanut butter. As of February 19, a total of 654 cases in 44 states had been identified (see the CDC website). The organism has been found in jars of King Nut creamy peanut butter, which is distributed to establishments such as long-term care facilities, prisons/detention centers, hospitals, schools, universities, and restaurants, but is not sold directly to consumers and is not known to be distributed for retail sale in grocery stores. There is also preliminary evidence of an association between illness and consumption of pre-packaged peanut butter crackers, specifically with Austin and Keebler brands, which are made with peanut butter paste manufactured in the same facility as King Nut peanut butter. For a full list of recalled products, go to the FDA website. Salmonella infections are characterized by diarrhea, fever, and abdominal cramps starting 12 to 72 hours after infection and usually lasting 4 to 7 days. Most people recover uneventfully, though a small number require hospitalization. For the time being, those living or traveling to the United States should avoid consuming any peanut-butter-containing products, such as cookies, crackers, cereal, candy and ice cream, until information becomes available about whether that product may be affected by the current outbreak.

In June 2008, a nationwide Salmonella outbreak was caused by contaminated jalapeno and serrano peppers from Mexico. As of late August, a total of 1442 persons in 43 states had been affected (see MMWR and the CDC website). A multi-state outbreak of Salmonella infections caused by Banquet brand frozen pot pies was reported in October 2007. In June 2007, a multi-state outbreak of Salmonella Wandsworth infections was reported, apparently caused by consumption of Veggie Booty, a snack of puffed rice and corn with a vegetable coating manufactured by Robert’s American Gourmet. As of June 28, a total of 52 cases had been identified, none fatal. In February 2007, an outbreak of Salmonella Tennessee infections was reported, caused by contamination of bulk peanut butter at a ConAGra processing plant in Georgia. In retrospect, the outbreak probably began in August 2006. More than 600 people across the country were affected. The Food and Drug Administration (FDA) advises consumers not to eat any Peter Pan or Great Value peanut butter beginning with the 2111 product code on the jar lid. Contaminated peanut butter was also used to make dessert toppings marketed by Sonic, Carvel, and J. Hungerford Smith. For further information, go to the CDC website at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5621a1.htm and http://www.cdc.gov/salmonella/wandsworth_062807.htm, and the Food and Drug Administration at http://www.fda.gov/bbs/topics/NEWS/2007/NEW01574.html.

Measles outbreaks continue to be reported from the United States, chiefly involving unvaccinated schoolchildren. Recent outbreaks occurred in Illinois (DuPage County, Cook County, and Lake County) in May 2008; Washington state (Grant County) in April 2008; Arizona in February 2008; San Diego, California in January-February 2008; and New York City in early 2008. All travelers born after 1956 should make sure they have had either two documented measles or MMR immunizations or a blood test showing measles immunity. This does not apply to people born before 1957, who are presumed to be immune. Children greater than 12 months of age should be given two doses of MMR vaccine, separated by one month, before travel.

An increased number of cases of mumps was reported from the state of Maine in November 2007, probably related to a major mumps outbreak occurring north of the border in Nova Scotia and New Brunswick. In April 2006, a major outbreak of mumps was reported from the state of Iowa, resulting in 1487 cases as of May. A smaller number of cases were reported from the states of Illinois, Kansas, Missouri, Nebraska, Pennsylvania, South Dakota, and Wisconsin. Most cases occurred in those between the ages of 18 and 25. For further information, go to MMWR. Mumps is a viral infection which is spread by direct contact with or inhalation of oral or nasal secretions from an infected person. All travelers born after 1956 should make sure they have had either two documented mumps or MMR immunizations or a blood test showing mumps immunity. This does not apply to people born before 1957, who are presumed to be immune. Children greater than 12 months of age should be given two doses of MMR vaccine, separated by one month, before travel.

Six cases of hantavirus pulmonary syndrome, four of the fatal, were reported from rural areas in the state of Colorado in the first seven months of 2007, and six cases (one fatal) were reported in the first eight months of 2008. In Colorado, the incidence usually peaks in May, June and July. Five cases were reported from the Benton-Franklin Health District in the state of Washington during the first eight months of 2007 and two cases were reported in August 2008 from south-central Washington. One case was reported from North Dakota and one from Utah in September 2008. Three cases were reported from New Mexico between May and November 2007, one in March 2008, one in December 2008, and one in May 2009. One occurred in South Dakota in October 2007. Two cases were reported from Texas and one case each from California and from Pennsylvania in July 2007. Between January and March, 2006, an increase in the number of cases of hantavirus pulmonary syndrome was reported from the states of Arizona, New Mexico, North Dakota, Texas, and Washington, apparently related to environmental conditions that promoted an increase in the rodent population. Two cases were reported from Los Angeles County, California, in July-August 2006. For further information, go to MMWR and ProMED-mail (July 18, 2007). The hantavirus pulmonary syndrome is a life-threatening infection characterized by high fevers, fluid in the lungs and respiratory failure. The virus is carried by rodents, especially the deer mouse. Most cases occur in those whose homes have been infested with rodents or contaminated with rodent excrement. Most travelers are at extremely low risk.

An outbreak of E. coli O157:H7 infections was reported in September 2006 from contaminated spinach grown on a farm in Salinas Valley, California. The spinach was processed and widely distributed by a company called Natural Selection Foods LLC. A total of 205 persons in 26 states were affected, including three fatalities. Two more outbreaks of E. coli O157:H7 infections occurred in December 2006: the first among those who had eaten at Taco Bell fast food restaurants in the northeastern part of the country and the second among customers at an unrelated fast food chain (Taco John) in Minnesota and Iowa. Both outbreaks were probably spread by contaminated lettuce, but DNA fingerprinting indicated the two outbreaks were not connected. The main symptom of E. coli O157:H7 infection is diarrhea, which is often bloody and often associated with crampy abdominal pain. The chief complication is hemolytic-uremic syndrome, which can lead to kidney failure and sometimes death. Any traveler to the United States who develops diarrhea after eating spinach or after eating at a Taco Bell restaurant should seek immediate medical attention. For further information, go to the Centers for Disease Control.

A cluster of Q fever cases was reported from Iowa in November 2006. The source of the cases has not been determined. Symptoms of Q fever typically include fever, chills, nausea, headache, and body aches. Complications may include pneumonia, hepatitis, endocarditis (heart valve infection), and infections of the bones and joints. In pregnant women, Q fever may lead to miscarriage. Q fever is primarily a disease of ruminants such as cattle, sheep, and goats, which shed the Q fever bacteria in their body fluids, especially birth products. Humans become infected by inhaling dust or aerosols contaminated by body fluids from infected animals. The disease is not transmitted from person-to-person.

An outbreak of tick paralysis was reported in August 2006 from the mountains of north-central Colorado. Four cases were identified, none of them fatal. See MMWR for further information. Tick paralysis is a rare disease thought to be caused by a toxin in tick saliva. The paralysis, which begins in the legs and moves upward, usually resolves within 24 hours after tick removal, though some people are left with residual weakness. Tick precautions, as below, are recommended for all travelers to the Colorado mountains.

An increased number of cases of plague was reported from four states in the year 2006: New Mexico (seven cases), Colorado (four cases, all in La Plata County), California (two cases), and Texas (one case). This was the largest number of cases reported in a single year in the United States since 1994. Five additional cases were reported from New Mexico between April and September, 2007, and two from Arizona between September and November, 2007. An additional case was reported form New Mexico (Eddy County) in January 2008 and two more cases from New Mexico (Santa Fe County) in June 2009. For further information, go to MMWR and ProMED-mail.

There are three forms of human plague: bubonic plague, characterized by enlarged, tender regional lymph nodes; septicemic plague, often causing nausea, vomiting, diarrhea, and abdominal pain; and pneumonic plague, associated with shortness of breath, chest pain, and a cough with bloody sputum. The plague is usually transmitted by the bite of rodent fleas. Those at greatest risk include those residing in rodent-infested dwellings and those participating in outdoor recreational activities, particularly rabbit hunting, in areas where plague is known to occur. The risk for most travelers is extremely low. There is no vaccine at present. To minimize risk, travelers should avoid areas containing rodent burrows or nests, never handle sick or dead animals, and follow insect protection measures, as described below.

An outbreak of tick-borne relapsing fever was reported from Lake Tahoe in August 2006. Many cases occurred in those who had stayed in rustic, rodent-infested cabins. See ProMED-mail for further information. One case was reported from San Luis Obispo County in northern California in June 2009. Relapsing fever is caused by bacteria known as spirochetes, closely related to the organisms that cause Lyme disease. The illness is characterized by periods of fever, chills, headaches, body aches, muscle aches, and cough, alternating with periods when the fever subsides and the person feels relatively well. Complications may include bleeding abnormalities, pneumonia, meningitis, cranial nerve palsies, hemiplegia, and coma. Tetracycline, erythromycin, and penicillin have all been used to treat relapsing fever. The first dose of antibiotic is often followed by a severe reaction (Jarisch-Herxheimer reaction) marked by fever, shaking chills, and a fall in blood pressure. There is no vaccine for relapsing fever. To prevent relapsing fever, visitors to Lake Tahoe should avoid sleeping in rustic cabins, unless they are known to be free of rodents, and should follow >tick precautions, as below.

Outbreaks of West Nile virus occur annually in the United States in the late summer and fall. For a map showing the current distribution of West Nile cases, go to the U.S. Geological Survey or the Centers for Disease Control. West Nile virus is carried by Culex mosquitoes, which breed in stagnant water and are most active after dusk. Most infections are mild or asymptomatic, but the virus may infect the central nervous system, leading to fever, headache, confusion, lethargy, coma, and sometimes death. There is no treatment for West Nile virus. Insect protection measures are advised from August to November in most parts of the United States.

An increased number of cases of leptospirosis was reported from Hawaii in 2004. Leptospirosis is acquired by exposure to water contaminated by the urine of infected animals. The disease is characterized by flu-like symptoms and rash, sometimes complicated by meningitis, jaundice and kidney failure. The Hawaii State Department of Health recommends that those with cuts or abrasions should not swim, wade or play in fresh water, and all swimmers in fresh water should keep their heads out of the water. The department reports that "known exposure sites and all state and county parks that have fresh water streams or ponds are regularly posted with leptospirosis warning signs." For further information, go to Hawaii State Department of Health website at http://kumu.icsd.hawaii.gov/health/about/pr/2004/04-30%20lepto.html.

A number of cases of Vibrio infections, chiefly Vibrio vulnificus, have been reported among survivors of Hurricane Katrina. See MMWR for further information. Vibrio vulnificus is a bacterium which may cause skin infections when open wounds are exposed to seawater. Those with limited immune defenses may develop a severe and life-threatening illness characterized by fever and chills, blood-tinged blistering skin lesions, and dangerously low blood pressure. All wounds, cuts and bites should be thoroughly cleansed with large amounts of soap and clean water. Any traveler to this region who develops a fever or skin infection after exposure to seawater or brackish water should immediately seek medical attention.

A number of less serious illnesses were reported among relief workers and hurricane survivors in the initial weeks following the storms. A variety of skin conditions were observed, including methicillin-resistant Staphylococcus aureus (MRSA) infections at an evacuee facility in Dallas, Texas, and cases of tinea corporis and folliculitis among military personnel. Clusters of diarrheal disease, mostly viral, were observed among persons in various evacuation centers. The number of these cases began to fall as health conditions improved. For further information, go to MMWR.

• Lyme disease (transmitted by ticks, mainly in the late spring and summer; most documented cases occur in the northeastern part of the country, especially New York, New Jersey, Connecticut, and Massachusetts; cases also reported from the northern Midwest and the northern Pacific coastal regions, including northern California)
• Ehrlichiosis and anaplasmosis (transmitted by ticks; cause flu-like symptoms, including fever, headache, malaise, and muscle aches; most cases occur between May and September, generally in rural areas; see Emerging Infectious Diseases)
• Coccidioidomycosis (fungal infection limited to semi-arid areas in the southwestern part of the country, including California's San Joaquin Valley; southern regions of Arizona, Utah, Nevada, and New Mexico; and western Texas; increased number of cases reported from California 2000-2007; acquired by inhalation of dust from contaminated soil; begins as a lung infection, causing fever, chest pain, and cough; may spread to other organs, particularly the nervous system, skin, and bone; see MMWR)
• Histoplasmosis (fungal infection prevalent in the Ohio-Mississippi Valley, particularly the states of Missouri, Kentucky, Tennessee, Indiana, Ohio, and southern Illinois; acquired by inhalation of dust from contaminated soil, often high-nitrogen soil fertilized with bird or bat droppings; usually causes pneumonia)
• Rocky Mountain spotted fever (transmitted by ticks; causes fever, headache, and muscle aches, followed by a rash; may be complicated by pneumonia, meningitis, gangrene, or kidney failure; despite the name, which points to where the disease was discovered, about half of all cases occur in the south Atlantic region, especially North Carolina, mostly between May and August)
• Tularemia (most cases reported from the central states of Arkansas, Missouri, Oklahoma, and South Dakota; outbreak reported among campers on the west side of Utah Lake in July 2007; single case reported from Cape May County in New Jersey in July 2007; outbreaks among rabbits reported from several parts of Wyoming in October 2006; infection transmitted by tick or deerfly bites or by handling the carcass of an infected animal; occasional cases caused by inhalation of an infectious aerosol, especially in Martha's Vineyard; may develop as a flu-like illness, pneumonia, or skin ulcers with swollen glands, depending upon how the infection is acquired)
• Arbovirus diseases (a group of mosquito-borne infections, rare but life-threatening; includes St. Louis encephalitis, Eastern equine encephalitis, Western equine encephalitis, La Crosse encephalitis, Powatan encephalitis; for an up-to-date map showing the distribution of these diseases in the United States, go to the U.S. Geological Survery)
• Angiostrongylus meningitis (three cases reported from Hawaii in January 2009; see ProMED-mail; January 6 and March 26, 2009; caused by Angiostrongylus cantonensis, a parasitic roundworm which humans acquire by eating infected snails or slugs, or raw vegetables which contain a small snail or slug)

When visiting rural or forested areas in the warm weather months, wear long sleeves, long pants, hats and boots, with pants tucked in. Apply insect repellents containing 25-50% DEET (N,N-diethyl-3-methylbenzamide) or 20% picaridin (Bayrepel) to exposed skin (but not to the eyes, mouth, or open wounds). DEET may also be applied to clothing. Products with a lower concentration of either repellent need to be repplied more frequently. Products with a higher concentration of DEET carry an increased risk of neurologic toxicity, especially in children, without any additional benefit. Do not use either DEET or picaridin on children less than two years of age. Perform a thorough tick check at the end of each day with the assistance of a friend or a full-length mirror. Ticks should be removed with tweezers, grasping the tick by the head. Many tick-borne illnesses can be prevented by prompt tick removal.

Bring adequate supplies of all medications in their original containers, clearly labeled. Carry a signed, dated letter from the primary physician describing all medical conditions and listing all medications, including generic names. If carrying syringes or needles, be sure to carry a physician's letter documenting their medical necessity.Pack all medications in hand luggage. Carry a duplicate supply in the checked luggage. If you wear glasses or contacts, bring an extra pair. If you have significant allergies or chronic medical problems, wear a medical alert bracelet.

Make sure your health insurance covers you for medical expenses abroad. If not, supplemental insurance for overseas coverage, including possible evacuation, should be seriously considered. If illness occurs while abroad, medical expenses including evacuation may run to tens of thousands of dollars. Bring your insurance card, claim forms, and any other relevant insurance documents. Before departure, determine whether your insurance plan will make payments directly to providers or reimburse you later for overseas health expenditures.

For an ambulance in the United States, call 911.

High quality medical care is widely available, but expensive. For a medical emergency, the best course is to locate the nearest hospital and go to its emergency room. The most sophisticated medical care is found at the university hospitals, though superb medical care is often available in community hospitals and the waits are usually shorter. If the problem isn’t urgent, you can call a nearby hospital and ask for a referral to a local physician, which is usually cheaper than a trip to the emergency room. You should avoid stand-alone, for-profit urgent care centers, which tend to perform large numbers of expensive tests, even for minor illnesses. Pharmacies are abundantly supplied, but you may find that some medications which are available over-the-counter in your home country require a prescription in the United States.

All children should be up-to-date on routine childhood immunizations, as recommended by the American Academy of Pediatrics. Children who are 12 months or older should receive a total of 2 doses of MMR (measles-mumps-rubella) vaccine, separated by at least 28 days, before international travel. Children between the ages of 6 and 11 months should be given a single dose of measles vaccine. MMR vaccine may be given if measles vaccine is not available, though immunization against mumps and rubella is not necessary before age one unless visiting a country where an outbreak is in progress. Children less than one year of age may also need to receive other immunizations ahead of schedule (see the accelerated immunization schedule).

Be sure to pack a medical kit when traveling with children. In addition to the items listed for adults, bring along plenty of disposable diapers, cream for diaper rash, and appropriate antibiotics for common childhood infections, such as middle ear infections.