1. Risks of disease from contaminated food or water to travelers
a. Types of disease
1 Traveler’s diarrhoea (TD) affects 20-50% of travelers
2 Hep A 1.6-20 cases per 1000 travelers per month
3 Typhoid 3-30 cases per 100,000 travelers per month
4 Biotoxin poisoning - ciguatera, scombroid
5 Brucellosis, tuberculosis, listeriosis
6 Hep E
7 cholera
8 polio
b. Higher risk travelers include
1 young children
2 immunodeficient travelers
c. Geographic risk
1 TD - high risk(20-75% of travellers) Latin America, Africa. Asia, parts of
the Middle East
- intermediate risk (8-20%) China, southern Europe, Israel, South Africa,
Russia, Caribbean ( Haiti and Dominican Republic)
- low risk in Canada, USA, northern Europe, Australia, Japan, some of
the Caribbean countries
2 Ciguatera poisoning - higher risk in the subtropical and tropical insular areas of the South Pacific, the Caribbean and Indian Oceans
d. Seasonal Risk
3 TD - higher risk in summer and rainy season
2. Food Contamination
( a more common cause of disease in travelers than water contamination)
a. At Source
4 shellfish - harvested from polluted water containing Hep A, aeromonas, salmonella, V. cholera or other Vibrio species
5 chicken, beef - fecally contaminated at slaughter i.e. ETEC, salmonella
6 lettuce or raw vegetables - fecally contaminated in the field by the practice in some developing countries i.e. China, of using human faeces as fertiliser
7 unpasteurized dairy products - brucellosis, listeriosis, tuberculosis
8 tropical reef fish, most commonly barracuda, also red snapper, grouper, jack, sea bass and moray eel can contain ciguatera toxin
9 beef, pork, fish, shellfish encysted with parasitic larvae causing trichinosis, tapeworm, liver fluke, lung fluke
10 aquatic plants like watercress or water chestnuts with parasitic cysts attached to the roots
b. Inadequate hygiene
1 lack of hand washing (both restaurant personnel and traveller)
2 foods requiring a lot of touching during prep and not cooked following i.e. salads
3 foods washed in the local water supply
4 lack of knowledge of good food hygiene i.e. cutting surfaces not cleaned
c. Inadequate Refrigeration or Inadequate Cooking Temperatures
1 lack of refrigeration causing bacterial overgrowth, i.e. food poisoning from staphylococci
2 inadequate reheating of leftovers causing bacterial overgrowth i.e. B.cereus in rice
3 Scombroid fish species such as bluefin and yellowfin tuna, mackerel, bonito, and other species such as mahimahi, herring, jack and bluefish contain high levels of histidine. With inadequate refrigeration histadine converts to histamine with resultant flushing, nausea, vomiting, diarrhoea and urticaria when ingested.
3. Water Contamination Causes
1 in many developing countries, sewage may drain into sources of drinking water causing contamination
2 limited treatment facilities
3 limited or non-existent public health inspection
4. Precautions
a. Immunization
1 Hepatitis A
2 Polio
3 Typhoid
4 Cholera - not recommended for the average traveler, for disaster or relief workers only
b. Avoidance
1 avoid drinking untreated tap water
2 avoid locally bottled or uncapped bottled water which may have been filled with untreated tap water
3 avoid brushing of teeth in untreated tap water
4 avoid ice cubes in drinks which may have been made from unclean water
5 avoid raw or rare meat, fish or shellfish. Steamed crabs or clams may not be heated sufficiently to kill Vibrio species
6 avoid fish species which are known to contain biotoxins. Note cooking will not destroy ciguatera toxin.
7 avoid raw vegetables especially leafy salads which may have been washed in unclean water
8 avoid aquatic plants in the Orient (watercress, water chestnuts)
9 avoid raw or undercooked eggs
10 avoid unpasteurized milk or dairy products
11 avoid street vendor food
12 avoid food left sitting out especially dairy
13 avoid reheated foods and leftovers as they may not have been heated sufficiently to kill pathogens
14 avoid swallowing water in pools (clorination may be inadequate) or even in the ocean (nearby sewage outlets?)
c. Hygiene
1 frequent handwashing especially prior to eating or preparing food. Use soap and water or commercially available hand sanitizers
2 observe hygiene in restaurants i.e. clean dishware, well-groomed staff, clean toilets, exposed garbage or flies?
d. Safe Food and Water “boil it, cook it, peel it or forget it”
1 commercially bottled water, seals intact
2 commercially bottled or canned soft drinks, fruit juices, beer and wine. Carbonation reduces pH creating a bactericidal environment.
3 boiled water i.e. tea, coffee
4 treated water (see below)
5 irradiated milk, canned milk, boiled milk, reconstituted dried milk from safe sources
6 thoroughly and recently cooked meats and fish served piping hot (internal temp should reach 70C or158F)
7 cooked fruits and vegetables and fruits peeled by oneself
8 foods cooked in advance should be held at a temperature of less than 10C or 50F
5. Water Purification
a. Boiling
1 the most reliable method
2 Bringing water to a boil for 1 minute will kill bacterial and parasitical causes of disease at all altitudes. At low altitudes viruses will be killed.
3 At higher altitudes above 2000m water should be boiled for 3 minutes to kill viruses or a chemical disinfectant used if boiled for 1 minute.
4 A pinch of salt improves the taste of boiled water.
b. Chemical Disinfection
1 More practical than boiling.
2 Under proper conditions iodine and chlorine are excellent for eliminating bacteria and viruses however they can be relatively ineffective against protozoal cysts such as giardia or cryptosporidium. Filtration must be used to remove these.
3 Iodine is more reliable as chlorine’s effectiveness varies greatly due to pH, temperature and organic content of water.
4 Various products are available such as tincture of iodine 2%, easier to carry iodine tablets - tetraglycine hydroperiodide, liquid chlorine bleach 4-6 % Clorox.
5 In general, cloudy water requires straining or filtration prior to treatment, a larger dose or a longer contact time. Cold water may be warmed or require a longer contact time.
6 Newer products contain chlorine dioxide which does kill giardia and cryptosporidia.
7 Iodine treated water is recommended for short -term use i.e. 3 weeks in any 6 month period. Long term use may cause suppression of the thyroid. Persons with thyroid disease should avoid iodinated water. It is not recommended for pregnant women as iodine in large doses may cause neonatal goitre or hypothyroidism. If no other alternatives short-term use i.e. <2-3 weeks is probably safe.
8 adding Vit C will improve the taste and smell of iodinated water
c. Filtration
1 removes bacteria and protozoa not viruses
2 removal of bacteria requires an absolute pore size of .2 microns
3 removal of protozoa requires an absolute pore size of 3-5 microns for giardia and entamoeba histolytica; 1-3 microns for cryptosporidium
4 viruses can be as small as 0.0004 microns so no filter will strain them out. Water must be chemically treated following filtration to kill viruses.
5 there are a variety of filters in different pore sizes, some are designed to avoid only large organisms i.e. giardiasis in alpine hikers
6 carbon filters will help to remove chemical and organic pollutants that affect colour, taste and odor of water
7 drawbacks of filtration - small pore size filters may clog easily and require frequent cleaning - this can be offset by prefiltering or adding a flocculant such as alum; few published scientific reports on the efficacy of specific filter brands.
d. Water purification device
1 filter with an attached demand-release iodine resin to kill viruses
2 a carbon cartridge third stage will reduce residual iodine content
References
1. Jung & McMullen; The Travel and Tropical Medicine Manual, 1995
2. Keystone, J.S.; Don’t drink the water..., 2000
3. Rose, Stewart; International Travel and Health Guide, 2001
4. Ansdell V.E. & Ericsson, C.D.; Prevention and Empiric Treatment of Traveler’s Diarrhea, Medical Clinics of North America: Vol. 83 Number 4 July 1999
5. Diemert, David J.; Prevention and Self-treatment of Traveler’s Diarrhea, Primary Care: Clinics in Office Practice Vol. 29 Number 4 Dec 2002
6. Yellow Book: Health Information for International Travel