CDC's International Travelers' Health Information
Safe Food and Water

The following is general information concerning prevention of recognition and prevention of food borne illnesses. For more complete travel health information, view the CDC website at http://www.cdc.gov/travel/foodwater.htm

RISKS FROM FOOD AND DRINK

April 5, 2004

Contaminated food and drink are common sources for the introduction of infection into the body. Among the more common infections that travelers can acquire from contaminated food and drink are Escherichia coli infections, shigellosis or bacillary dysentery, giardiasis, cryptosporidiosis, Norwalk-like viruses, and hepatitis A. Other less common infectious disease risks for travelers include typhoid fever and other salmonelloses, cholera, rotavirus infections, and a variety of protozoan and helminthic parasites (other than those that cause giardiasis and cryptosporidiosis). Many of the infectious diseases transmitted in food and water can also be acquired directly through the fecal-oral route.

Food

To avoid illness, travelers should be advised to select food with care. All raw food is subject to contamination. Particularly in areas where hygiene and sanitation are inadequate, the traveler should be advised to avoid salads, uncooked vegetables, and unpasteurized milk and milk products such as cheese, and to eat only food that has been cooked and is still hot or fruit that has been peeled by the traveler personally. Undercooked and raw meat, fish, and shellfish can carry various intestinal pathogens. Cooked food that has been allowed to stand for several hours at ambient temperature can provide a fertile medium for bacterial growth and should be thoroughly reheated before serving. Consumption of food and beverages obtained from street food vendors has been associated with an increased risk of illness. The easiest way to guarantee a safe food source for an infant <6 months of age is to have the infant breast feed. If the infant has already been weaned from the breast, formula prepared from commercial powder and boiled water is the safest and most practical food.

Some species of fish and shellfish can contain poisonous biotoxins, even when well cooked. The most common type of biotoxin in fish is ciguatoxin. The flesh of the barracuda is the most toxic laden and should always be avoided. Red snapper, grouper, amberjack, sea bass, and a wide range of tropical reef fish contain the toxin at unpredictable times. The potential for ciguatera poisoning exists in all subtropical and tropical insular areas of the Caribbean and the Pacific and Indian Oceans where the implicated fish species are eaten. Symptoms of ciguatera poisoning include gastroenteritis followed by neurologic problems such as dysesthesias, temperature reversal, weakness, and, rarely, hypotension. Scombroid is another common fish poisoning that occurs worldwide in tropical as well as temperate regions. Fish of the Scombridae family (e.g., bluefin, yellowfin tuna, mackerel, and bonito), as well as some nonscombroid fish (e.g., mahimahi, herring, amberjack, and bluefish) may contain high levels of histidine in their flesh. With improper refrigeration or preservation, histidine is converted to histamine, which can cause flushing, headache, nausea, vomiting, diarrhea, and urticaria.

Cholera cases have occurred in people who ate crab brought back from Latin America by travelers. Travelers should be advised not to bring perishable seafood with them when they return to the United States from high-risk areas. Also, the incorrect assumption is often made that food and water aboard commercial aircraft are safe. Food and water may be obtained in the country of departure where items may be contaminated as well.

Water

Water that has been adequately chlorinated, by using minimum recommended water treatment standards used in the United States, will afford substantial protection against viral and bacterial waterborne diseases. However, chlorine treatment alone, as used in the routine disinfection of water, might not kill some enteric viruses and the parasitic organisms that cause giardiasis, amebiasis, and cryptosporidiosis. In areas where chlorinated tap water is not available or where hygiene and sanitation are poor, travelers should be advised that only the following might be safe to drink:

• Beverages, such as tea and coffee, made with boiled water.
• Canned or bottled carbonated beverages, including carbonated bottled water and soft drinks.
• Beer and wine.

Treatment of Water with Tincture of Iodine

Where water might be contaminated, travelers should be advised that ice should also be considered contaminated and should not be used in beverages. If ice has been in contact with containers used for drinking, travelers should be advised to thoroughly clean the containers, preferably with soap and hot water, after the ice has been discarded.

It is safer to drink a beverage directly from the can or bottle than from a questionable container. However, water on the outside of beverage cans or bottles might also be contaminated. Therefore, travelers should be advised to dry wet cans or bottles before they are opened and to wipe clean surfaces with which the mouth will have direct contact. Where water might be contaminated, travelers should be advised to avoid brushing their teeth with tap water.

Treatment of Water

Travelers should be advised of the following methods for treating water to make it safe for drinking and other purposes.

Boiling

Boiling is by far the most reliable method to make water of uncertain purity safe for drinking. Water should be brought to a vigorous rolling boil for 1 minute and allowed to cool to room temperature; ice should not be added. This procedure will kill bacterial and parasitic causes of diarrhea at all altitudes and viruses at low altitudes. To kill viruses at altitudes >2,000 m (6,562 ft), water should be boiled for 3 minutes or chemical disinfection should be used after the water has boiled for 1 minute. Adding a pinch of salt to each quart or pouring the water several times from one clean container to another will improve the taste.

Chemical Disinfection

Chemical disinfection with iodine is an alternative method of water treatment when it is not feasible to boil water. However, this method cannot be relied on to kill Cryptosporidium unless the water is allowed to sit for 15 hours before it is drunk. Two well-tested methods for disinfection with iodine are the use of tincture of iodine (Table 4–1) and tetraglycine hydroperiodide tablets (e.g., Globaline, Potable-Aqua, or Coghlan's). These tablets are available from pharmacies and sporting goods stores. The manufacturers' instructions should be followed. If water is cloudy, the number of tablets used should be doubled; if water is extremely cold (<5° C; <41° F]), an attempt should be made to warm the water, and the recommended contact time should be increased to achieve reliable disinfection. Cloudy water should be strained through a clean cloth into a container to remove any sediment or floating matter, and then the water should be boiled or treated with iodine.

Chlorine, in various forms, can also be used for chemical disinfection. However, its germicidal activity varies greatly with the pH, temperature, and organic content of the water to be purified; therefore, it can produce less consistent levels of disinfection in many types of water. Chemically treated water is intended for short-term use only. If iodine-disinfected water is the only water available, it should be used for only a few weeks.

Water Filters

Portable filters currently on the market will provide various degrees of protection against microbes. Reverse-osmosis filters provide protection against viruses, bacteria, and protozoa, but they are expensive, are larger than most filters used by backpackers, and the small pores on this type of filter are rapidly plugged by muddy or cloudy water. In addition, the membranes in some filters can be damaged by chlorine in water. Microstrainer filters with pore sizes in the 0.1- to 0.3-µm range can remove bacteria and protozoa from drinking water, but they do not remove viruses. To kill viruses, travelers using microstrainer filters should be advised to disinfect the water with iodine or chlorine after filtration, as described previously. Filters with iodine-impregnated resins are most effective against bacteria, and the iodine will kill some viruses; however, the contact time with the iodine in the filter is too short to kill the protozoa Cryptosporidium and, in cold water, Giardia.

Filters that are designed to remove Cryptosporidium and Giardia carry one of the four messages below—verbatim—on the package label.

• Reverse osmosis
• Absolute pore size of 1 micron or smaller
• Tested and certified by NSF Standard 53 or NSF Standard 58 for cyst removal
• Tested and certified by NSF Standard 53 or NSF Standard 58 for cyst reduction

Filters may not be designed to remove crypto if they are labeled only with these words:

• Nominal pore size of <1 micron
• One micron filter
• Effective against Giardia
• Effective against parasites
• Carbon filter
• Water purifier
• EPA approved (Caution: EPA does not approve or test filters.)
• EPA registered (Caution: EPA does not register filters for crypto removal)
• Activated carbon
• Removes chlorine
• Ultraviolet light
• Pentiodide resins
• Water softener

Filters collect organisms from water. Anyone changing cartridges should wear gloves and wash hands afterwards. Filters may not remove crypto as well as boiling does because even good brands of filters may sometimes have manufacturing flaws that allow small numbers of organisms to pass through the filter. In addition, poor filter maintenance or failure to replace filter cartridges as recommended by the manufacturer can cause a filter to fail.

A travelers' guide to buying water filters for preventing cryptosporidiosis and giardiasis can be found at URL: www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/factsht_crypto_prevent_water.htm. These two organisms are either highly (cryptosporidium) or moderately (Giardia) resistant to chlorine; so conventional halogen disinfection may be ineffective. Boiling water or filtration can be used as an alternative to disinfection. Many filters that remove parasites may not be able to kill or remove smaller organisms.

Proper selection, operation, care, and maintenance of water filters are essential to producing safe water. The manufacturers' instructions should be followed. NSF International, an independent testing company, tests and certifies water filters for their ability to remove protozoa, but not for their ability to remove bacteria or viruses. Few published scientific reports have evaluated the efficacy of specific brands or models of filters against bacteria and viruses in water. Until such information becomes available, CDC cannot identify which specific brands or models of filters are most likely to remove bacteria and viruses. To find out if a particular filter is certified to remove cryptosporidia, contact NSF International by calling 1-877-867-3435; by fax to 313-769-0109; or by writing to 789 North Dixboro Road, P.O. Box 130140, Ann Arbor, Michigan 48113-0140; or online at http://www.NSF.org/certified/DWTU/. Under "Reduction claims for drinking water treatment units—health effects," check the box in front of the words "Cyst Reduction."

As a last resort, if no source of safe drinking water is available or can be obtained, tap water that is uncomfortably hot to touch might be safer than cold tap water; however, proper disinfection, filtering, or boiling is still advised.

TRAVELERS' DIARRHEA

Who gets travelers' diarrhea?

Travelers' diarrhea (TD) is the most common illness affecting travelers. Each year between 20%-50% of international travelers, an estimated 10 million persons, develop diarrhea. The onset of TD usually occurs within the first week of travel but may occur at any time while traveling, and even after returning home. The most important determinant of risk is the traveler's destination. High-risk destinations are the developing countries of Latin America, Africa, the Middle East, and Asia. Persons at particular high-risk include young adults, immunosuppressed persons, persons with inflammatory-bowel disease or diabetes, and persons taking H-2 blockers or antacids. Attack rates are similar for men and women. The primary source of infection is ingestion of fecally contaminated food or water.

What are common symptoms of travelers' diarrhea?

Most TD cases begin abruptly. The illness usually results in increased frequency, volume, and weight of stool. Altered stool consistency also is common. Typically, a traveler experiences four to five loose or watery bowel movements each day. Other commonly associated symptoms are nausea, vomiting, diarrhea, abdominal cramping, bloating, fever, urgency, and malaise. Most cases are benign and resolve in 1-2 days without treatment. TD is rarely life-threatening. The natural history of TD is that 90% of cases resolve within 1 week, and 98% resolve within 1 month.

What causes travelers' diarrhea?

Infectious agents are the primary cause of TD. Bacterial enteropathogens cause approximately 80% of TD cases. The most common causative agent isolated in countries surveyed has been enterotoxigenic Escherichia coli (ETEC). ETEC produce watery diarrhea with associated cramps and low-grade or no fever. Besides ETEC and other bacterial pathogens, a variety of viral and parasitic enteric pathogens also are potential causative agents.

What preventive measures are effective for travelers' diarrhea?

Travelers can minimize their risk for TD by practicing the following effective preventive measures:

• Avoid eating foods or drinking beverages purchased from street vendors or other establishments where unhygienic conditions are present
• Avoid eating raw or undercooked meat and seafood
• Avoid eating raw fruits (e.g., oranges, bananas, avocados) and vegetables unless the traveler peels them.
• If handled properly well-cooked and packaged foods usually are safe. Tap water, ice, unpasteurized milk, and dairy products are associated with increased risk for TD. Safe beverages include bottled carbonated beverages, hot tea or coffee, beer, wine, and water boiled or appropriately treated with iodine or chlorine.

Is prophylaxis of travelers' diarrhea recommended?

CDC does not recommend antimicrobial drugs to prevent TD. Studies show a decrease in the incidence of TD with use of bismuth subsalicylate and with use of antimicrobial chemoprophylaxis. Several studies show that bismuth subsalicylate taken as either 2 tablets 4 times daily or 2 fluid ounces 4 times daily reduces the incidence of travelers' diarrhea. The mechanism of action appears to be both anti-bacterial and antisecretory. Use of bismuth subsalicylate should be avoided by persons who are allergic to aspirin, during pregnancy, and by persons taking certain other medications (e.g., anticoagulants, probenecid, or methotrexate). In addition, persons should be informed about potential side effects, in particular about temporary blackening of the tongue and stool, and rarely ringing in the ears. Because of potential adverse side effects, prophylactic bismuth subsalicylate should not be used for more than 3 weeks.

Some antibiotics administered in a once-a-day dose are 90% effective at preventing travelers' diarrhea; however, antibiotics are not recommended as prophylaxis. Routine antimicrobial prophylaxis increases the traveler's risk for adverse reactions and for infections with resistant organisms. Because antimicrobials can increase a traveler's susceptibility to resistant bacterial pathogens and provide no protection against either viral or parasitic pathogens, they can give travelers a false sense of security. As a result, strict adherence to preventive measures is encouraged, and bismuth subsalicylate should be used as an adjunct if prophylaxis is needed.

What treatment measures are effective for travelers' diarrhea?

TD usually is a self-limited disorder and often resolves without specific treatment; however, oral rehydration is often beneficial to replace lost fluids and electrolytes. Clear liquids are routinely recommended for adults. Travelers who develop three or more loose stools in an 8-hour period—-especially if associated with nausea, vomiting, abdominal cramps, fever, or blood in stools—-may benefit from antimicrobial therapy. Antibiotics usually are given for 3-5 days. Currently, fluoroquinolones are the drugs of choice. Commonly prescribed regimens are 500 mg of ciprofloxacin twice a day or 400 mg of norfloxacin twice a day for 3-5 days. Trimethoprim-sulfamethoxazole and doxycycline are no longer recommended because of the high level of resistance to these agents. Bismuth subsalicylate also may be used as treatment: 1 fluid ounce or 2 262 mg tablets every 30 minutes for up to eight doses in a 24-hour period, which can be repeated on a second day. If diarrhea persists despite therapy, travelers should be evaluated by a doctor and treated for possible parasitic infection.

When should antimotility agents not be used to treat travelers' diarrhea?

Antimotility agents (loperamide, diphenoxylate, and paregoric) primarily reduce diarrhea by slowing transit time in the gut, and, thus, allows more time for absorption. Some persons believe diarrhea is the body's defense mechanism to minimize contact time between gut pathogens and intestinal mucosa. In several studies, antimotility agents have been useful in treating travelers' diarrhea by decreasing the duration of diarrhea. However, these agents should never be used by persons with fever or bloody diarrhea, because they can increase the severity of disease by delaying clearance of causative organisms. Because antimotility agents are now available over the counter, their injudicious use is of concern. Adverse complications (toxic megacolon, sepsis, and disseminated intravascular coagulation) have been reported as a result of using these medications to treat diarrhea.

What is CDC doing to prevent travelers' diarrhea?

CDC, in collaboration with the World Health Organization and several Ministries of Health, is working to improve food and water safety around the world. CDC also investigates risk factors associated with acquisition of TD, to assist in identifying more effective preventive measures. CDC continues to monitor antimicrobial resistance in other countries and in the United States. In addition, CDC, in collaboration with international agencies, is working to improve sanitary conditions in foreign accommodations (e.g., tourist resorts) and frequently consults with travel medicine specialists and local and state health departments. CDC is responsible for evaluating sanitation on cruise ships docking in US ports.

Please visit CDC's Traveler's Health site for more information about the vessel sanitation program and for a summary of recent vessel inspections.

How can I learn more about travelers' diarrhea?

Potential travelers should consult with a doctor or a travel medicine specialist before departing on a trip abroad. Information about TD is available from your local or state health departments or the World Health Organization (WHO).

Other information that may be of interest to travelers can be found at the CDC Travelers' Health homepage at http://www.cdc.gov/travel.

BOVINE SPONGIFORM ENCEPHALOPATHY AND VARIANT CREUTZFELDT-JAKOB DISEASE

Date last revised: June 30, 2003

Description

Since 1996, strong evidence has accumulated for a causal relationship between ongoing outbreaks in Europe of a disease in cattle called bovine spongiform encephalopathy (BSE, or "mad cow disease") and a disease in humans called variant Creutzfeldt-Jakob disease (vCJD). Both disorders, which are caused by an unconventional transmissible agent, are invariably fatal brain diseases with unusually long incubation periods, measured in years. The specific foods associated with transmission of the agent from cattle to humans are unknown; however, bioassays have identified the BSE agent in the brain, spinal cord, retina, dorsal root ganglia, distal ileum, and bone marrow of cattle experimentally infected by the oral route.

Occurrence

From 1995 through June 2002, 124 human cases of vCJD were reported in the United Kingdom (UK), 6 in France, and 1 case each in Ireland, Italy, and the United States. The patients from Ireland and the United States had both lived in the UK for >5 years during the BSE epidemic there. From 1986 through 2001, >98% of BSE cases worldwide were reported from the UK, where the disease was first described. During this same period, the number of countries reporting at least one indigenous BSE case increased: 4 such European countries through 1993, 8 through 1998, and 18 through 2001. As of July 2002, two countries outside Europe—Japan and Israel—reported their first indigenous BSE cases. The proportion of the annual total number of BSE cases worldwide reported outside the UK increased to >25% in 2000 and >45% in 2001. This increase reflected the declining large (>182,000 total cases) epidemic of BSE in the UK and the increasing number of other countries with improved surveillance and higher rates of BSE.

In 2001, only two countries, the UK and Portugal, reported a BSE incidence rate of >100 indigenous cases per million cattle >24 months of age. The reported BSE rates for other countries were Republic of Ireland, 62 cases per million; Switzerland, 49 per million; Belgium, 28; Spain, 24; Germany, 20; France, 20; Slovakia, 18; Italy, 14; and the Netherlands, 10. The reported rates for Denmark, Slovenia, Greece, the Czech Republic, Finland, Japan, and Austria ranged from 1 to 7 cases per million. The numbers of reported BSE cases and incidence rates, by country, are available on the Internet website of the Office International des Epizooties, at http://www.oie.int/eng/info/en_esb.htm.

In addition to the countries with confirmed BSE in 2001, by June 2002 the European Union's Scientific Steering Committee had classified 14 other countries as likely to have BSE or confirmed as having BSE at a lower level. These countries were Albania, Bulgaria, Croatia, Cyprus, Estonia, Hungary, Latvia, Lithuania, Luxembourg, Poland, Romania, San Marino, Slovenia, and Turkey.

In January 2002, the U.S. Food and Drug Administration published guidance to reduce the theoretical risk of transmission to humans by blood and blood products. This document included a list of European countries with BSE or possible increased risk of BSE that could be used for determining blood donor referrals. One deferral criterion was living cumulatively for 5 years or more in Europe from 1980 to the present. Among European countries listed were Bosnia-Herzegovina, Liechtenstein, Macedonia, Norway, Sweden, and Yugoslavia. Information is being generated rapidly on BSE issues, and updated sources should be consulted

Risk for Travelers

The current risk of acquiring vCJD from eating beef (muscle meat) and beef products produced from cattle in countries with at least possibly increased risk of BSE cannot be determined precisely. Among many uncertainties affecting this determination are the incubation period between exposure to the infective agent and onset of illness, the ultimate number and age distribution of vCJD cases in the UK that will result from earlier BSE exposures, the sensitivities of each country's surveillance for BSE and vCJD, the compliance with and effectiveness of public health measures instituted in each country to prevent BSE contamination of human food, and details about cattle products from one country distributed and consumed elsewhere. Nevertheless, in the UK, the current risk of acquiring vCJD from eating beef and beef products appears to be extremely small, approximately 1 case per 10 billion servings. In the other countries of the world, this current risk, if it exists at all, would not likely be any higher than that in the UK, particularly if BSE-related, public health control measures are being well implemented. Such measures would be especially important in a country such as Portugal, which like the UK has a relatively high incidence rate of reported BSE. Despite the exceedingly low risk, the U.S. blood donor deferral criteria focus on the time (cumulatively 3 months or more) that a person lived in the UK from 1980 through 1996, whereas for the rest of Europe the criteria focus on the time (cumulatively 5 years or more) that a person lived in these countries from 1980 through the present. The lack of a time limit on the latter criterion reflects uncertainties related to human food chain protection in some countries outside the UK, as well as concerns about overly complicating the screening questions posed to prospective U.S. blood donors.

Prevention

Public health control measures, such as surveillance, culling sick animals, or banning specified risk materials, have been instituted in European countries to prevent potentially BSE-infected tissues from entering the human food chain. The most stringent of these control measures, including a program that excludes all animals >30 months of age from the human food and animal feed chains, have been applied in the UK and appear to be highly effective. In June 2000, the European Union Commission on Food Safety and Animal Welfare strengthened the European Union's BSE control measures by requiring all member states to remove specified risk materials from animal feed and human food chains as of October 1, 2000; such bans had already been instituted in most member states. These control measures include banning the use of mechanically recovered meat from the vertebral column of cattle, sheep, and goats for human food and BSE testing of all cattle >30 months of age destined for human consumption.

To reduce any risk of acquiring vCJD from food, travelers to Europe or other areas with indigenous cases of BSE may consider either avoiding beef and beef products altogether or selecting beef or beef products, such as solid pieces of muscle meat (rather than brains or beef products such as burgers and sausages), that might have a reduced opportunity for contamination with tissues that may harbor the BSE agent. Milk and milk products from cows are not believed to pose any risk for transmitting the BSE agent.