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Risks from Food and Drink
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.
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.
Table 4–1.
Treatment of water with tincture of iodine
 |
Clear water |
Cold or cloudy
water† |
| 2% |
5 |
10 |
|
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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.
— Dennis
Juranek, Steve Luby, James Maguire, Eric Mintz
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