Water Disinfection for International Travelers

SECTION 2

CHAPTER 6

THE PRE-TRAVEL CONSULTATION

Water Disinfection for International Travelers Howard Backer

KEYPOINTS

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Risk of water-borne illness depends on the number of organisms consumed (volume of water, concentration of organisms) host factors, and the treatment system efficacy An understanding of the unique vocabulary of terms such as disinfection and purification is necessary for the travel medicine practitioner in order to be able to educate the traveler



Methods of water treatment include the use of heat, clarification, filtration and chemical disinfection



The use of appropriate concentrations of halogens (e.g. chlorine and iodine) is popular for water disinfection, though there may be some toxicity

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Different microorganisms have varying susceptibilities to heat, filtration, and chemical disinfection

INTRODUCTION Safe and efficient treatment of drinking water is among the major public health advances of the twentieth century. Without it, water-borne disease would spread rapidly in most public water systems served by surface water.1 However, worldwide, more than 1 billion people have no access to potable water, and 2.4 billion do not have adequate sanitation. This results in billions of cases of diarrhea every year and a reservoir of enteric pathogens for travelers to these areas.2 In certain tropical countries, the influence of high-density population, rampant pollution, and absence of sanitation systems means that available raw water is virtually wastewater. Contamination of tap water commonly occurs because of antiquated and inadequately monitored disposal, water treatment, and distribution systems.3 Travelers have no reliable resources to evaluate local water system quality. Less information is available for remote surface water sources.4 Even in developed countries with low rates of diarrhea illness, regular water-borne disease outbreaks indicate that microbiologic quality of the water, especially surface water, is not assured.5 Indeed, it was not only with natural disasters such as the recent tsunami, but also in the aftermath of hurricane Katrina within the USA that the most important public health problem was a lack of potable water. As a result, travelers should take appropriate steps to ensure that the water they drink does not contain infectious agents. Look, smell, and taste are not reliable indicators to estimate water safety.

ETIOLOGY AND RISK OF WATER-BORNE ­INFECTION Infectious agents with the potential for water-borne transmission ­include bacteria, viruses, protozoa, and non-protozoan parasites (Table 6.1). Although the primary reason for disinfecting drinking water is to destroy microorganisms from animal and human biologic wastes, water may also be contaminated with industrial chemical pollutants, organic or inorganic material from land and vegetation, biologic organisms from animals, or organisms that reside in soil and water. E. coli and Vibrio cholerae may be capable of surviving indefinitely in tropical water. Most enteric organisms, including Shigella, S. typhi, hepatitis A, and Cryptosporidium parvum, can retain viability for long periods in cold water and can even survive for weeks to months when frozen in water. Survival of enteric bacterial and viral pathogens in temperate water is generally only several days; however, E. coli O157:H7 can survive 12 weeks at 25°C.6 Risk of water-borne illness depends on the number of organisms consumed, which is in turn determined by the volume of water, concentration of organisms, and treatment system efficiency.7 Additional factors include virulence of the organism and defenses of the host. Microorganisms with a small infectious dose (e.g. Giardia, Cryptosporidia, Shigella spp., hepatitis A, enteric viruses, enterohemorrhagic E. coli) may cause illness even from inadvertent drinking during ­waterbased recreational activities.8 Because total immunity does not develop for most enteric pathogens, reinfection may occur. Most ­ diarrhea among travelers is probably food-borne; however, the capacity for ­water-borne transmission must not be underestimated. Travelers should also be aware of the risk of infection from inadvertent ingestion during recreational activities, although its prevention is problematic.9

WATER TREATMENT METHODS FOR ­TRAVELERS Several techniques for improving microbiologic quality of water are available to individuals and small groups who encounter questionable water supplies while traveling (Table 6.2). As with all advice in travel medicine, the specific recommendation for any traveler depends on the destination and the style and purpose of travel. Most travelers should become familiar with more than one technique. Travelers may stay in hotels at night and explore remote villages or wilderness parks during the day, which requires an understanding of various methods for a spectrum of water conditions. Bottled water may be a convenient and popular solution but creates ecological problems in countries that do not recycle the plastic. The term disinfection, the desired result of field water treatment, is used here to indicate the removal or destruction of harmful ­microorganisms, which reduces the risk of illness. It is impractical to eliminate all microorganisms from drinking water; generally the goal is a 3–5 log reduction (99.9–99.999%). Table 6.3 lists other important definitions.

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SECTION 2: THE PRE-TRAVEL CONSULTATION

   Table 6.1     Water-borne pathogens50-52 Bacterial

Viral

Protozoan

Other parasitesa

Enterotoxigenic E. coli; E. coli O157:H7

Hepatitis A

Giardia intestinalis

Ascaris lumbricoides

Shigella species

Hepatitis E

Entamoeba histolytica

Ancylostoma duodenale

Campylobacter species

Norovirus

Cryptosporidium parvum

Fasciola hepatica

Vibrio cholerae

Poliovirus

Blastocystis hominis

Dracunculus medinensis

Salmonella (primarily typhi) species

Miscellaneous enteric viruses (>100 types)

Isospora belli

Strongyloides stercoralis

Yersinia enterocolitica

Balantidium coli

Trichuris trichiura

Aeromonas

Acanthamoeba

Clonorchis sinensis

Cyclospora

Paragonimus westermani Diphyllobothrium latum Echinococcus granulosus

aWater-borne

transmission is possible but uncommon for all these parasites except D. medinesis.

   Table 6.2     Methods of water treatment that can be applied by travelers Heat Clarification Sedimentation Coagulation-flocculation Granular activated charcoal Filtration Reverse osmosis Halogens Chlorine Iodine Iodine resins Miscellaneous Chlorine dioxide and mixed species Silver Ultraviolet

Heat Heat is the oldest and most reliable means of water disinfection (Table 6.4). Heat inactivation of microorganisms is exponential and follows first-order kinetics.10 Thus, the thermal death point is reached in shorter time at higher temperatures, while lower temperatures are effective if applied for a longer time. Pasteurization uses this principle to kill enteric food pathogens and spoiling organisms at temperatures between 60°C (140°F) and 70°C (158°F), well below boiling, for up to 30 min.11 All common enteric pathogens are readily inactivated by heat, though microorganisms vary in heat sensitivity (Table 6.5). Bacterial spores such as Clostridium spp. are heat resistant (some can survive 100°C [212°F] for long periods) and ubiquitous in the natural environment, but they are not water-borne enteric pathogens. Thus, sterilization, the destruction or removal of all life forms, is not necessary for drinking water. Since enteric pathogens are killed within seconds by boiling ­ water and rapidly at temperatures above 60°C (140°F), the traditional advice to boil water for 10 min to assure potable water is excessive. Because the time required to heat water from 55°C (131°F) to a boil works toward disinfection, any water brought to a boil should be adequately ­disinfected. Boiling for 1 min or keeping the water covered and allowing it to cool slowly after boiling will add an extra margin of safety. The boiling point

decreases with increasing altitude but this is not significant compared with the time required for thermal death at these temperatures. Although attaining boiling temperature is not necessary, boiling is the only easily recognizable endpoint without using a thermometer. Hot tap water temperature and the temperature of water perceived to be too hot to touch vary too widely to be reliable measures for pasteurization of water. Nevertheless, if no reliable method of water treatment is available, tap water that has been kept hot in a tank for at least 30 min and is too hot to keep a finger immersed for 5 s (estimated 55–65°C; [131–149°F]) is a reasonable alternative. Travelers with access to electricity can boil water with either a small electric heating coil or a lightweight electric beverage warmer brought from home. In very austere and desperate situations with a hot, sunny climate, adequate pasteurization temperature can be achieved with a solar oven or simple reflectors.12

Clarification Clarification refers to techniques that reduce turbidity, or cloudiness, of surface water that is caused by natural organic and inorganic material. These techniques can markedly improve the appearance and taste of water. They may reduce the number of microorganisms, but not enough to assure potable water. However, clarifying the water facilitates disinfection by filtration or chemical treatment. Cloudy water can rapidly clog micro-filters. Moreover, cloudy water requires increased levels of halogens for treatment and the combined effects of the water contaminants plus the additional halogen can be quite unpleasant to taste.

Sedimentation Sedimentation is the separation of suspended particles like sand and silt that are large enough to settle rapidly by gravity. Microorganisms, especially protozoan cysts, also settle eventually, but this takes much longer. Sedimentation should not be considered a means of disinfection. Simply allow the water to sit undisturbed for about 1 h or until sediment has formed on the bottom of the container, then decant or filter the clear water from the top.

Coagulation-flocculation Coagulation-flocculation (C-F), a technique in use since 2000bc, can remove smaller suspended particles and chemical complexes too small to settle by gravity (colloids).13 Coagulation is achieved with the ­ addition of a chemical that causes particles to stick together by

CHAPTER 6: Water Disinfection for International Travelers

   Table 6.3     Definition of terms Clarification

Techniques that reduce turbidity of water

Coagulation-flocculation

Removes smaller suspended particles and chemical complexes too small to settle by gravity (colloids)

Contact time

The length of time that the halogen is in contact with microorganisms in the water

Disinfection

The desired result of field water treatment, used here to indicate the removal or destruction of harmful microorganisms

Enteric pathogen

Microorganisms capable of causing intestinal infection after ingested; may be transmitted through food, water, or direct fecal–oral contamination

Halogen

Oxidant chemical that can be used for disinfection of water

Halogen demand

The amount of halogen reacting with impurities in the water

Potable

Implies ‘drinkable’ water, but technically means that a water source, on average, over a period of time, contains a ‘minimal microbial hazard,’ so that the statistical likelihood of illness is acceptable

Purification

Frequently used interchangeably with ‘disinfection,’ but is more accurately used to indicate the removal of organic or inorganic chemicals and particulate matter to improve offensive color, taste, and odor

Residual halogen concentration

The amount of active halogen remaining after halogen demand of the water is met

Reverse osmosis

A process of filtration that uses high pressure to force water through a semi-permeable membrane that filters out dissolved ions, molecules, and solids

Turbidity

Cloudiness in water caused by natural organic and inorganic material

   Table 6.4     Heat for disinfection Advantages

Disadvantages

Does not impart additional taste or color to water

Does not improve the taste, smell or appearance of poor quality water

Can pasteurize water without sustained boiling

Fuel sources may be scarce, expensive, or unavailable

Single-step process that inactivates all enteric pathogens Efficacy is not compromised by contaminants or particles in the water, as with halogenation and filtration Relative susceptibility of microorganisms to heat: Protozoa > Bacteria > Viruses.

   Table 6.5     Heat inactivation of microorganisms (selected data)53–55 Organism

Lethal temperature/time

Giardia

70°C for 10 min

Cryptosporidium

heated up to 72°C over 1 min

Salmonella, Shigella, and Campylobacter

75°C for 3 min

V. cholerae

60°C for 10 min or 100°C for 10 s

E. coli

60°C for 5 min or 70°C for 1 min

Enteric viruses

56–60°C for 20–40 min or >70°C (158°F) for <1 min.

Hepatitis A

85°C for 1 min

electrostatic and ionic forces. Flocculation is a physical process that promotes formation of larger particles by gentle mixing. Alum (an aluminum salt), lime (alkaline chemicals principally containing calcium or magnesium with oxygen), or iron salts are commonly used coagulants. Alum is non-toxic and used in the food industry for pickling. It is readily available in any chemical supply store. In an emergency, baking powder or even the fine white ash from a campfire can be used as a coagulant. Other natural substances are used in various parts of the world. C-F removes 60–98% of microorganisms, heavy metals, and some chemicals and minerals (Table 6.6).

The amount of alum added in the field, approximately a large pinch (one-eighth teaspoon) per gallon (3.79 L) of water, need not be precise. Stir or shake briskly for 1 min to mix, and then agitate gently and frequently for at least 5 min to assist flocculation. If the water is still cloudy, add more flocculent and repeat mixing. After at least 30 min for settling, pour the water through a fine-woven cloth or paper ­filter. Although most microorganisms are removed with the floc, a final process of filtration or halogenation should be completed to ensure disinfection. Several products combine coagulation-flocculation with halogen disinfection.14

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   Table 6.6     Coagulation-flocculation Advantages

Disadvantages

Highly effective to clarify water and remove many microorganisms

Unfamiliar technique and substances to most travelers

Improves efficacy of filtration and chemical disinfection

Adds extra step unless combined flocculent-disinfectant tablet

Inexpensive and widely available Simple process with no toxicity Relative susceptibility of microorganisms to coagulation-flocculation: Protozoa > Bacteria = Viruses.

   Table 6.7     Microorganism susceptibility to filtration Organism

Approximate size (μm)

Maximum recommended filter rating (μm)

Viruses

0.03

Not specifieda

Escherichia coli

0.5 × 3–8

0.2–0.4

Campylobacter

0.2–0.4 × 1.5–3.5

0.2–0.4

V. cholerae

0.5 × 1.5–3.0

0.2–0.4

Cryptosporidium oocyst

2–6

1

Giardia cyst

6–10 × 8–15

3–5

Entamoeba histolytica cyst

5–30 (average 10)

3–5

Nematode eggs

30–40 × 50–80

20

Schistosome cercariae Dracunculus larvae

50 × 100 20 × 500

Coffee filter or fine cloth, or double thickness closely woven cloth

aMost

portable filters, except reverse osmosis membrane filters, rely on electrostatic trapping of viruses or viral attachment to larger particles.

Granular-activated carbon Granular-activated carbon (GAC) purifies water by adsorbing organic and inorganic chemicals, thereby improving odor and taste. GAC is a common component of field filters. It may trap but does not kill organisms; in fact, non-pathogenic bacteria readily colonize GAC.15 In field water treatment, GAC is best used after chemical disinfection, to make water safer and more palatable by removing disinfection by-products and pesticides, as well as many other organic chemicals and heavy metals. It removes the taste of iodine and chlorine from water (see Halogens).

Filtration Filtration is both a physical and a chemical process influenced by characteristics of filter media, water, and flow rate. The primary determinant of a microorganism’s susceptibility to filtration is its size (Table 6.7). Portable filters can readily remove protozoan cysts and bacteria, but may not remove all viruses, which are much smaller than the pore size of most field filters.16 The semi-permeable membranes in reverse osmosis filters are inherently capable of removing viruses (see below). However, viruses often clump together or to other larger particles or organisms, and electrochemical attraction may cause viruses to adhere to the filter surface. Through these mechanisms, mechanical filters using ceramic elements with a pore size of 0.2 μm, can reduce viral loads by 2–3 logs, but should not be considered adequate for complete removal of viruses. Two portable filters have been able to meet the US EPA standards for water purifiers, which include 4log removal of viruses: First-Need filter (General Ecology, Exton, PA), which functions through a combination of filtration and electrostatic attraction,17 and Sawyer Biologic viral filter (Sawyer Products, Safety Harbor, FL), which is composed of microtubules with an absolute pore size of 0.02 μm.

There are a large number of filters available commercially for individuals and for small groups, and their ease of use is attractive to many travelers (Table 6.8). Most of the filters sold for field water treatment are maze, or depth, filters made of various media (including ceramic, compressed GAV, or fibers) that create long, irregular labyrinthine passages to trap the organism. A depth filter has a large holding capacity for particles, so it lasts longer than a single-layer membrane filter before clogging. Flow can be partially restored to a clogged filter by back flushing or surface cleaning, as with ceramic filters, which removes the larger particles trapped near the surface. Most filters incorporate a pre-filter on the intake tubing to remove large particles, protecting the inner micro-filter; if lacking, a fine-mesh cloth or coffee filter can be used. See clarification techniques for cloudy water. In pristine protected watersheds where human activity (and viral contamination) is minimal and the main concerns are bacteria and cysts, mechanical filtration alone can provide adequate disinfection. However, for developing world travel and for surface water with heavy levels of fecal or sewage contamination, most mechanical filters are not adequate as the sole means of disinfection. Additional treatment with heat or halogens before or after filtration guarantees effective virus removal. Several factors influence the decision of which filter to buy: (1) how many persons are to use the filter; (2) what microbiologic demands will be put on the filter (product claims); and (3) what is the preferred means of operation (function). Cost may also be an important consideration (Table 6.9).

Reverse osmosis Reverse osmosis filtration uses high pressure (100–800 PSI) to force water through a semi-permeable membrane that filters out dissolved ions, molecules, and solids. This process can both remove microbiologic contamination and desalinate water. Although

CHAPTER 6: Water Disinfection for International Travelers

   Table 6.8     Filtration Advantages

Disadvantages

Simple to operate

Add bulk and weight to baggage

Mechanical filters require no holding time for treatment (water is treated as it passes through the filter

Most filters not reliable for removal of viruses

Large choice of commercial products

Expensive relative to halogens

Add no unpleasant taste and often improve taste and appearance of water

Channeling of water or high pressure can force microorganisms through the filter

Rationally combined with halogens for removal or destruction of all microorganisms

Eventually clog from suspended particulate matter; may require some maintenance or repair in field

Susceptibility of microorganisms to filtration: Protozoa > Bacteria > Viruses.

   Table 6.9     Portable field water filters and purification devices Manufacturer, product (Manufacturer’s website)a

Microbial claimsb

Operation

Primary filter, additional elements, stages. Commentsc

Capacity

Retail price (US$)d

Aquamira (www.mcnett.com)

P

Sport bottle

Carbon filter, 2 μm, in a squeeze bottle. May be used in ­conjunction with Aquamira water treatment – chlorine dioxide stabilized solution or tablets

1–2 person

19

Aquarain (www.aquarain.com)   Aquarain 200 P, B

Gravity drip

Small group

189

  Aquarain 400

P, B

Gravity drip

Stacked bucket filter with two ceramic elements. Carbon core, stainless steel housing Bucket filter, four ceramic elements Carbon core, stainless steel housing

Large group

199

British Berkfeld (www.jamesfilter.com)   Big Berkey

P, B

Gravity drip

Large group

249

  LP-2

P, B

Gravity drip

Bucket filter, four ceramic elements with carbon matrix. Available in ­stainless steel or Lexan housing Bucket filter, two ceramic elements Plastic housing

Small group

145

1–2 person

30

Small group Large group

90 500

Small group

150

1–2 person

80; 130

1–2 person

45; 50

1–2 person

60; 85

Small group

60

General Ecology (www.generalecology.com)

  Microlite

P

  First-Need Deluxe   Base Camp

P, B, V P, B, V

  Trav-L-Pure

P, B

Hydro-Photon (www.hydrophoton.com) Steri-Pen Water Purifier, Adventurer

P, B, V

Claims for viral removal are based on electrostatic attraction in structured matrix compressed carbon block filter. Variety of sizes and ­configurations also available for in-line use and electric powered units Hand pump Intake strainer, GAV, biocide tablets for suspected bacterial and viral ­contamination Hand pump Compressed charcoal Hand pump or electric Compressed charcoal element similar to First-Need. High flow, high ­capacity. Stainless steel housing. Prefilter. ­Electric models also available Hand pump Same compressed charcoal filter ­element as First-Need in plastic housing Hand held purifier

Katadyn (www.katadyn.com)   Exstream; Exstream XR

P, B, V

Sport bottle

  Hiker; Guide

P

Hand pump

  Basecamp

P, B

Gravity drip

Ultraviolet purifier uses batteries with timer. Active end of unit is held in bottle or other small container of water Unless otherwise specified, filter ­elements are 0.2 μm ceramic depth filter Iodine resin with filter for ­protozoan cysts, and granular activated ­charcoal Pleated glass-fiber 0.3 μm filter with granular activated charcoal core and prefilter; for high quality source water, removes ‘most’ bacteria Pleated glass fiber 0.3 μm with activated carbon; reservoir bag with in-line filter

Continued

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SECTION 2: THE PRE-TRAVEL CONSULTATION

   Table 6.9     Portable field water filters and purification devices–cont’d Manufacturer, product (Manufacturer’s website)a

Microbial claimsb

Operation

Primary filter, additional elements, stages. Commentsc

Capacity

Retail price (US$)d

  Mini   Pocket   Ceradyn; Gravidyn

P, B P, B P, B

Hand pump Hand pump Gravity drip

1–2 person Small group Small–large group

90 190 160; 190

  Combi

P, B

Hand pump

Small group

160

  Expedition

P, B

Hand pump

Large group

890

  Survivor 06; Survivor 35

P, B, V

Hand pump

Ceramic filter with prefilter Ceramic filter with prefilter Bucket filter, three ceramic candles; optional activated carbon core filters with Gravidyn Ceramic filter and activated carbon cartridge; can be converted for in-line faucet use Ceramic filter with intake prefilter; stainless steel housing Reverse osmosis filter; desalinates as well as disinfects, for ocean survival; very low flow rate; power units available

1–2 person

750; 1900

MSR (www.msrcorp.com/filters)   Sweetwater MicroFilter

P, B

Hand pump

Small group

60

  Miniworks EX

P, B

Hand pump

Small group

80

  Waterworks EX

P, B

Hand pump

Small group

160

  Miox Purifier

P, B

Chemical purifier

0.2 μm depth filter with granular activated carbon and prefilter, purifier solution (chlorine) as pretreatment to kill viruses Ceramic filter with activated carbon core and prefilter Ceramic filter with activated carbon core, prefilter, and third stage ­membrane filter Battery operated 25 × 150 mm device produces disinfectant through ­electrolysis of water and salt

Small group

130

Sawyer (www.sawyerproducts.com)   Water filter

P, B

Sport bottle or in-line gravity drip

P, B, V

Sport bottle, in-line gravity drip, or faucet adaptor

1–2 person or small group 1–2 person or small group

40–60

  Water purifier

Hollow fiber filter, 0.1 μm; drink-through water bottle, in-line gravity drip from reservoir bag, or faucet attachment Hollow fiber filter 0.02 μm membrane; drink-through water bottle or in-line gravity drip from reservoir bag

Stern’s Outdoor Products (www.stearnsinc.com)   Outdoors Filter pump   Outdoors High flow

P P

Hand pump Gravity drip

Ceramic 0.5 μm filter and prefilter Ceramic 0.5 μm filter with activated carbon core; plastic collection bag

1–2 person Small group

26 70

Timberline (www.timberlinefilters.com)   Eagle   Basecamp

P, B P

Hand pump Gravity drip

1 μm filter; ultralight and unbreakable 2 μm filter; coated nylon reservoir bag

1–2 person Small group

26 66

70–120

aThis is not a comprehensive list. Models change frequently. Manufacturer website provided if it contains product information; otherwise search manufacturer and brand with any major search engine to find large retail sites that provide detailed product information. bP, protozoa; B, bacteria; V, viruses. cConsider additional features, such as flow rate, filter capacity, size, and filter weight. dPrices at time of writing. Prices vary.

small hand pump reverse osmosis units have been developed, their high price and slow output currently prohibit use by land-based travelers. They are, however, important survival aids for ocean voyagers.

Filter testing and registration The United States Environmental Protection Agency (EPA) ­developed consensus-based performance standards as a guideline for testing and evaluation of portable water treatment devices.18 Many companies now use the standards as their testing guidelines. Testing is done or contracted by the manufacturer. Challenge water at specified temperatures, turbidity, and numbers of

microorganisms is pumped through the filter at given intervals within the claimed volume capacity. Units that claim to remove, kill, or inactivate all types of disease-causing microorganisms from the water, including bacteria, viruses, and protozoan cysts, are designated as a ‘microbiologic water purifier.’ They must demonstrate that they meet the testing guidelines, which require a 3-log (99.9%) reduction for cysts, 4-log (99.99%) for viruses and 5–6 log reduction for bacteria. Filters can make limited claims to serve a definable environmental need, for example, removal of protozoan cysts or cysts and bacteria only. The EPA does not ­ endorse, test, or approve mechanical filters; it merely assigns registration numbers.

CHAPTER 6: Water Disinfection for International Travelers

   Table 6.10     Halogenation Advantages

Disadvantages

Inexpensive

Potential toxicity (especially iodine)

Iodine and chlorine are widely available

Corrosive, stains clothing

Very effective for bacteria, viruses, and Giardia

Not effective for Cryptosporidium

Taste can be removed

Imparts taste and odor

Flexible dosing

Flexibility requires understanding of disinfection principles

As easily applied to large quantities as small quantities Relative susceptibility of microorganisms to halogens: Bacteria > Viruses > Protozoa.

   Table 6.11     Dose of halogen for field water disinfection Iodination techniques

Amount for 4  ppma

Amount for 8  ppma

  Iodine tabs (tetraglycine hydroperiodide)     EDWGT (emergency drinking water germicidal tablet)     Potable Aqua     Globaline   2% iodine solution (tincture)

1/2 tab

1 tab

  Saturated solution: iodine crystals in water   Saturated solution: iodine crystals in alcohol

0.2 mL (5 gtts)b 0.35 mL (8 gtts)b 13 mL 0.1 mL

0.4 mL (10 gtts)b 0.70 mL (16 gtts)b 26 mL 0.2 mL

Chlorination techniques

Amount for 5 ppma

Amount for 10 ppma

  Sodium hypochlorite (household bleach) 5%

0.1 mL (2 gtts)b

0.2 mL (4 gtts)b ¼ tab/2 quarts 1 tab (8.5 mg NaDCC) 1 tab or packet

  10% povidone-iodine solutionc

  Calcium hypochlorite: Redi Chlor (1/10 g tab)   Sodium dichloroisocyanurate: AquaClear   Chlorine plus flocculating agent: Chlor-floc; PUR purifier sachets aAdded

to 1 L or quart of water. with dropper (1 drop = 0.05 mL) or small syringe. solutions release free iodine in levels adequate for disinfection, but scant data are available.

bMeasure

cPovidone-iodine

Halogens Worldwide, chemical disinfection with halogens, chiefly chlorine and iodine, is the most commonly used method for improving and maintaining microbiologic quality of drinking water and can be used by individuals and groups in the field (Table 6.10).19 Hypochlorite, the major chlorine disinfectant, is currently the preferred means of municipal water disinfection worldwide, so extensive data support its use. Both calcium hypochlorite (CaOCl2) and sodium hypochlorite (NaOCl) readily dissociate in water. Iodine is effective in low concentrations for killing bacteria, viruses, and cysts, and in higher concentration against fungi and even bacterial spores; however, it is a poor algicide. Elemental (diatomic) ­iodine (I2) and hypoiodous acid (HOI) are the major germicides in an aqueous solution. Bromine is another halogen with germicidal ­action that is sometimes used for treatment of swimming pool ­water, but has not been used for drinking water treatment in the field. The germicidal activity of halogens results from oxidation of essential cellular structures and enzymes. Disinfection effectiveness is determined by characteristics of the disinfectant, the microorganism, and ­environmental factors. Given adequate concentrations and contact times, both iodine and chlorine are effective disinfectants with similar biocidal ­activity under most conditions. Of the halogens, iodine reacts least readily with organic compounds and is less affected by pH, indicating that low iodine residuals should be more stable and persistent than correspond­ ing concentrations of chlorine. Taste preference is ­individual. Common sources and doses of iodine and chlorine are given in Table 6.11.

Chlorine is still advocated by the World Health Organization and the Centers for Disease Control and Prevention as a mainstay of large scale community, individual household, and emergency use.20 Vegetative bacteria (non-spore forming) are very sensitive to ­halogens; viruses have intermediate sensitivity, requiring higher concentrations or longer contact times. Protozoal cysts are more resistant than enteric bacteria and enteric viruses, but can be inactivated by field doses of halogens (Table 6.12).21–32 Cryptosporidium oocysts, however, are much more resistant to halogens and inactivation is not practical with common doses of iodine and chlorine used in field ­water ­disinfection.23 Little is known about Cyclospora, but it is ­assumed to be similar to Cryptosporidium. Certain parasitic eggs, such as ascaris, are also resistant, but these are not commonly spread by water. All these resistant cysts and eggs are susceptible to heat or filtration. Relative resistance between organisms is similar for iodine and chlorine.

The disinfection reaction Several factors influence the disinfection reaction. Understanding these allows flexibility with greater reassurance (Table 6.13). The primary factors of the first-order chemical disinfection reaction are concentration and contact time.24,25 Their relationship is illustrated in Figure 6.1. Concentrations of 1–16 mg/L for 10–60 min are generally effective. Even clear surface water often has at least 1 mg/L of halogen demand, so it is prudent to use 4 mg/L as a target halogen concentration for clear ­water.26 Lower concentrations (e.g. 2 mg/L) can be used for back-up treatment

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   Table 6.12     Halogen disinfection data24–32 Halogen

Organism

Concentration (mg/L)a

Time (min)

Temperature (°C)

Disinfection constant (Ct)b

Chlorine

Escherichia coli Campylobacter 20 enteric viruses Hepatitis A virus E. histolytica cysts Giardia cysts Cryptosporidium Oocyst Schistosome cercariae

  0.1   0.3   0.5   0.5   3.5   2.5 80 10   1.0

   0.16    0.5   60    5   10   60   90   70   30

5 25 2 5 25 5 20 28

0.016 0.15 30 2.5c 35 150 7200–9600 1440 30

Escherichia coli E. histolytica cysts E. histolytica cysts Poliovirus 1 Coxsackie virus Giardia cysts Giardia cysts

  1.3   3.5   6.0   1.25   0.5  4  4

   1   10    5   39   30   15 120

2–5 25 25 25 5 30 5

1.3 35 30 49 15 60d 480d

Iodine

aResidual

concentration of active chlorine disinfectant compounds. experiments use 2-3 log (99% to 99.9%) reduction as endpoint. c4-log reduction. d100% kill; viability tested only at 15, 30, 45, 60, and 120 min. bMost

   Table 6.13     Factors affecting halogen disinfection Effect

Compensation

Measured in mg/L or the equivalent, parts per million (ppm); higher concentration increases rate and proportion of microorganisms killed Usually measured in minutes; longer contact time assures higher proportion of organisms killed

Higher concentration increases rate and allows shorter contact time for equivalent results. Lower concentration requires increased contact time Contact time is inversely related to concentration; longer time allows lower concentration

 Temperature

Cold slows reaction time

 Water contaminants, cloudy water (turbidity)

Halogen reacts with organic nitrogen compounds from decomposition of organisms and their wastes to form compounds with little or no disinfecting ability, effectively decreasing the concentration of available halogen. In general, turbidity increases halogen demand The optimal pH for halogen disinfection is 6.5–7.5. As water becomes more alkaline, approaching pH 8.0, much higher doses of halogens are required

Some treatment protocols recommend doubling the dose (concentration) of halogen in cold water, but if time allows, exposure time can be increased instead, or the temperature of the water can be increased Doubling the dose of halogen for cloudy water is a crude means of compensation that often results in a strong halogen taste on top of the taste of the contaminants. A more rational approach is to first clarify water to reduce halogen demand

Primary factors  Concentration  Contact time Secondary factors

 pH

of questionable tap water (Table 6.14). The need for prolonged contact times with low halogen concentrations is suggested by (1) data that show extended contact times are required for 99.9% kill of Giardia in very cold water;27,28 and (2) uncertainty of residual concentration.

Iodine resins Iodine resins are considered demand disinfectants. The resin has low solubility, so that as water passes through, little iodine is released into aqueous solutions. On the other hand, when microorganisms contact the resin, iodine is transferred and binds to the microorganisms, ­ apparently aided by electrostatic forces.33 Bacteria and cysts are ­ effectively exposed to high iodine concentrations, which allow ­ reduced contact time compared with dilute iodine solutions. ­However, some contact time is necessary, especially for cysts. Resins have ­ demonstrated ­ effectiveness against bacteria, viruses, and cysts, but not against Cryptosporidium parvum oocysts or bacterial spores.

Most surface water is neutral to slightly acidic, so compensating for pH is not necessary. Tablet formulations of halogen have the advantage of some buffering capacity

The concept of demand disinfectants has great potential for water disinfection in small or individual systems.34 Filters containing iodine resins have been designed for field use. Most incorporate a 1 μm cyst filter to remove Cryptosporidium, Giardia, and other halogen-­resistant parasitic eggs or larva, in an attempt to avoid prolonged contact time. Carbon that removes residual dissolved iodine, preventing ­excessive iodine ingestion in long-term users, may not allow sufficient contact time for cyst destruction. However, without controlling residual ­iodine, high levels of iodine have been reported in effluent water in very hot climates, leading to thyroid problems among Peace Corps volunteers using the filters over a prolonged period of time.35 Cloudy or sediment-laden water may clog the resin, as it would any filter, or coat the resin, inhibiting iodine transfer. In summary, iodine resins are effective disinfectants that can be engineered into attractive field products, including use in the space shuttle and large-scale units for international disasters. The effectiveness of the

CHAPTER 6: Water Disinfection for International Travelers

   Table 6.14     Recommended contact time (minutes) for specified concentration of halogen and water temperaturea Concentration of halogen

5°C

15°C

2 ppm

240

180

60

4 ppm

180

60

45

60

30

15

8 ppm aContact

25°C

times are extended from usual recommendations to account for uncertainty of residual halogen and time necessary to kill Giardia cysts in very cold water.

Halogen concentration (mg/L)

Halogen toxicity

Protozoal cysts

10

Enteric virus 1.0 E.coli

1.0

10

100

Contact time (min) Figure 6.1:  Graph of disinfection reaction for 99.9% kill, halogen concentration versus time. Note relative susceptibility of ­microorganisms. Slope and position of lines will vary with specific ­organism, disinfectant, and water temperature. (Adapted from Chang SL, WHO Bulletin 1968; 38:401–414.)

resin is highly dependent on the product design and function. Several companies recently have abandoned iodine resin-containing portable hand-pump filters due to repeat testing that demonstrated viral breakthrough, despite initial pre-marketing testing that passed the EPA protocol. Only one drink-through bottle remains on the US market, but other products may still be available outside the USA. Iodine resins may prove useful for small communities in ­ undeveloped and rural areas where chlorine disinfection is technically and economically unfeasible.

Improving halogen taste Objectionable taste and smell limit the acceptance of halogens, but taste can be improved by several means. One method is to use the minimum necessary dose with a longer contact time. Several ­chemical means are available to reduce free iodine to iodide or chlorine to ­chloride that have no color, smell, or taste. These chemical species also have no disinfection action, and so these techniques should be used only after the required contact time. The best and most readily available agent is ascorbic acid (Vitamin C), available in crystalline or powder form. A common ingredient of flavored drink mixes, it accounts for their effectiveness in covering up the taste of halogens. Other safe and effective means of chemical reduction are sodium thiosulfate, hydrogen peroxide, and zinc-copper alloys (KDF ­resins) that act as catalysts to reduce free iodine and chlorine through an ­electrochemical reaction. GAV will remove the taste of iodine and chlorine partially by adsorption and partially by chemical reduction. Finally, alternative techniques such as filtration or heat that do not affect taste can be used in many situations.

Chlorine has no known toxicity when used for water ­disinfection. Sodium hypochlorite is not carcinogenic; however, reactions of chlorine with certain organic contaminants yield chlorinated ­hydrocarbons, chloroform, and other trihalomethanes, which are considered carcinogenic. Nevertheless, the risk of severe illness or even death from infectious diseases if disinfection is not used is far greater than any risk from by-products of chlorine disinfection. There is much more concern with iodine because of its physiologic activity, potential toxicity, and allergenicity. Data reviewed by Backer and Hollowell36 suggest the following guidelines as appropriate: n High levels of iodine (16–32 mg/day) such as those produced by recommended doses of iodine tablets should be limited to short periods of 1 month or less n Iodine treatments that produce a low residual ≤1–2 mg/L appear safe, even for long periods of time in people with normal thyroid glands n Anyone planning to use iodine for prolonged periods should have their thyroid examined and thyroid function tests done to assure that they are initially euthyroid. Optimally, repeat thyroid function test and examine for iodine goiter after 3–6 months of continuous iodine ingestion and monitor occasionally for iodine-induced goiter thereafter. If this is not feasible, assure low-level iodine consumption (see above) or use a different technique. Certain groups should not use iodine for water treatment: n pregnant women (due to concerns of neonatal goiter) n those with known hypersensitivity to iodine n persons with a history of thyroid disease, even if controlled on medication n persons with a strong family history of thyroid disease (thyroiditis) n persons from countries with chronic iodine deficiency.

Miscellaneous disinfectants Ozone and chlorine dioxide are both effective disinfectants that are widely used in municipal water treatment plants, but until recently, were not available in stable form for field use. These disinfectants have been demonstrated effective against Cryptosporidia in commonly used concentrations.37,38 New technology enables chlorine dioxide generation for use in an array of small-scale, on-site applications, including solutions (Aquamira: McNett Outdoor, Bellingham, WA and Pristine: Advanced Chemicals Ltd., Vancouver, BC), and tablets (MicroPur MP-1: Katadyn Corp, Wallisellen, Switzerland, and Aquamira) (Table 6.15). MicroPur tablets are US EPA registered as a ‘water purifier,’ while registration for Aquamira is pending demonstration of efficacy under various conditions. Aquamira drops solution is currently approved for sale in the USA under more ­limited bactericidal claims. Pristine, the equivalent product sold in Canada, makes full claims for protozoa, including Cryptosporidium (Pristine, Port Coquitlam, BC).

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SECTION 2: THE PRE-TRAVEL CONSULTATION

   Table 6.15     Chlorine dioxide Advantages

Disadvantages

Effective against all microorganisms, including Cryptosporidium

Volatile, so do not expose tablets to air and use generated solutions rapidly

Low doses have no taste or color

No persistent residual, so does not prevent recontamination during storage

Portable device now available for individual and small group field use and simple to use

Sensitive to sunlight, so keep bottle shaded or in pack during treatment

More potent than equivalent doses of chlorine Less affected by nitrogenous wastes Relative susceptibility of microorganisms to chlorine dioxide: Bacteria > Viruses > Protozoa.

A portable product developed for military use and recently transferred to the civilian market uses an electrochemical process to convert simple salt into a mixed-oxidant disinfectant containing free chlorine, chlorine dioxide and ozone.39 The Miox purifier has been reduced to a cigar-sized unit that operates on camera batteries (MSR Inc, Seattle, WA). Larger units for field use and small communities are also available (Miox Corp, Albuquerque, NM).

Citrus and potassium permanganate

Silver

Preferred technique

Silver ion has bactericidal effects in low doses and some attractive features, including absence of color, taste and odor. However, the concentrations are strongly affected by adsorption onto the surface of any container as well as common substances in water, and scant data for disinfection of viruses and cysts indicate limited effect, even at high doses. The use of silver as a drinking water disinfectant has been much more popular in Europe, where silver tablets (MicroPur, Katadyn Corp, Wallisellen, Switzerland) are sold widely for field water disinfection. The EPA has not approved them for this purpose in the USA, but they were approved as a water preservative, to prevent bacterial growth in previously treated and stored water. Recently, the company has combined a chlorine solution with the silver (Micropur Forte) to provide water disinfection plus preservation.

Ultraviolet Ultraviolet (UV) radiation is widely used to sterilize water for beverages and food products, for secondary treatment of wastewater, and to disinfect drinking water at the community and household level. It has not been well adapted to field use because of the requirements for power. In sufficient doses of energy, all water-borne enteric pathogens are inactivated by UV radiation. The ­ultraviolet waves must actually strike the organism, so the water must be free of particles that would act as a shield. The UV rays do not alter the water, but they also do not provide any ­residual disinfecting power. Recently a portable, battery operated unit was marketed for small quantity disinfection (Hydro-Photon Inc, Blue Hill, ME). Although previous data suggested limited ability of monochromatic UV rays to inactivate protozoan cysts, ­company product testing ­ appears solid and shows effectiveness against ­important water-borne pathogens, including Cryptosporidia. Simple, table-size UV units with low power requirements are available for international applications (WaterHealth, Lake Forest, CA). UV irradiation by sunlight can substantially improve microbiologic quality of water and reduce diarrheal illness in developing countries. Recent work has confirmed efficacy and optimal procedures of the solar disinfection (SODIS) technique. Transparent bottles (e.g. clear plastic beverage bottles) preferably lying on a dark surface are exposed to sunlight for a minimum of 4 h, with intermittent agitation.40 UV and thermal inactivation are strongly synergistic for the solar disinfection of drinking water.41

Both citrus juice and potassium permanganate have some demonstrated antibacterial effects in an aqueous solution. However, data are few and not available for effect on cysts. Either could be used in an emergency situation to decrease bacterial and viral contamination, but cannot be recommended as a primary means of water disinfection.

Optimal water treatment technique for an individual or group will depend on the number of persons to be served, space and weight ­accommodations, quality of source water, personal taste preferences, and fuel availability. Heat is effective as a one-step process in all situations, but will not ­improve the aesthetics of the water. Test data indicate that new chlorine ­ dioxide-generating techniques can be used as single step processes. Iodine resins, combined with microfiltration to remove resistant cysts, are also a viable one-step process, but questions have ­ recently surfaced of product effectiveness under all conditions, so few ­ products are available. Certain filters and ultraviolets may be effective single step processes. Since halogens do not kill Cryptosporidia and most filtration misses some viruses, optimal protection for all ­situations may require a two-step process of (1) filtration or ­coagulation-flocculation followed by (2) halogenation (Tables 6.16, 6.17).42,43 Where the water will be stored for a period of time, such as on a boat, motor home, or a home with rainwater collection, halogens, chlorine dioxide, or silver should be used to prevent the water from becoming contaminated after treatment. This can be supplemented by filtration before or after storage. A minimum chlorine or iodine free residual concentration of 3–5 mg/L should be maintained in the water. Iodine will work for short periods (i.e. weeks) but not for prolonged storage, since it is a poor algaecide. For prolonged storage, a tightly sealed container is best to decrease the risk of contamination. Narrow mouth jars or containers with water spigots prevent contamination from repeated contact with hands or utensils.44 On long-distance, ocean-going boats where sea water must be desalinated as well as disinfected during the voyage, only reverse osmosis membrane filters are adequate.

SANITATION Studies in developing countries have demonstrated a clear benefit in the reduction of diarrheal illness and other infections from safe drinking water, hygiene, and adequate sanitation; the benefit is greater when all are applied together, especially with appropriate education.45–47 Personal hygiene, particularly hand-washing, prevents spread of ­infection from food contamination during preparation of meals. Disinfection of dishes and utensils is accomplished by rinsing in water containing

CHAPTER 6: Water Disinfection for International Travelers

   Table 6.16     Summary of field water disinfection techniques

Heat

Bacteria

Viruses

Giardia/ Ameba

Cryptosporidium

Nematodes/Cercaria

+

+

+

+

+

Filtration

+

+/−a

+

+

+

Halogens

+

+

+

−

+/−b

Chlorine dioxide

+

+

+

+

+/−b

aMost

bEggs

filters make no claims for viruses. Reverse osmosis is effective. General ecology and sawyer viral purifier claim virus removal. are not very susceptible to halogens but very low risk of water-borne transmission.

   Table 6.17     Choice of method for various sources of water Source water ‘Pristine’ wilderness water with little human or  domestic animal activity

Tap water in  developing country

Developed or developing country Clear surface water near human and animal activitya

Cloudy water

Primary concern

Giardia, enteric bacteria

Bacteria, Giardia, small numbers of viruses

All enteric pathogens, including Cryptosporidium

All enteric pathogens plus microorganisms

Effective methods

Any single step methodb

Any single step method

1. Heat 2. Filtration plus halogen (can be done in either order); iodine resin filters (see text) 3. Chlorine dioxide 4. Ultraviolet (commercial product, not sunlight)

CF followed by second step (heat, filtration, or halogen)

CF, coagulation-flocculation. aIncludes agricultural run-off with cattle grazing, or sewage treatment effluent from upstream villages or towns. bIncludes heat, filtration, or halogens.

enough household bleach to achieve a distinct chlorine odor. Use of halogen solutions or potassium permanganate solutions to soak vegetables and fruits can decrease microbial contamination, especially if the surface is scrubbed to remove dirt or other particulates. Neither method reaches organisms that are ­embedded in ­surface crevices or protected by other particulate matter.48 The sanitation challenge for wilderness and rural travelers is proper waste disposal to prevent additional contamination of water supplies. Human waste should be buried 20–30 cm deep, at least 30 m from any water, and at a location from which water runoff is not likely to wash organisms into nearby water sources. Groups of three persons or more should dig a common latrine to avoid numerous individual potholes and ­inadequate disposal.

CONCLUSION Although food-borne illnesses probably account for most enteric problems that affect travelers, nearly all causes of travelers’ diarrhea can also be water-borne. It is not possible for travelers to judge the microbiologic quality of surface water, and it is not prudent to assume the potability of tap water in many areas. Many simple and effective field techniques to improve microbiologic water quality are available to travelers. It is important to learn the basic principles and limitations of heat, filtration, and chemical disinfection, and then become familiar with at least one technique appropriate for the destination, water source, and group composition. Detailed information about these techniques is also available in Auerbach’s textbook, Wilderness Medicine.49

References   1. World Health Organization. The Global Water Supply and Sanitation ­Assessment 2000, Geneva: WHO and UNICEF; 2000.   2. Pruss A, Kay D, Fewtrell L, Bartram J. Estimating the burden of disease from water, sanitation, and hygiene at a global level. Environ Health Perspect 2002; 110:537–542.   3. Wright J, Gundry S, Conroy R. Household drinking water in developing countries: a systematic review of microbiological contamination between source and point-of-use. Tropical Medicine and International Health 2004; 9:106–117.   4. Geldreich E. Microbiological quality of source waters for water supply. In: McFeters G, ed. Drinking Water Microbiology. New York: SpringerVerlag; 1990: 3–32.   5. CDC. Surveillance for waterborne-disease outbreaks – United States, 1999–2000. MMWR 2002; 51:1–48.   6. Wang G, Doyle M. Survival of enterohemorrhagic Escherichia coli O157:H7 in water. J Food Prot 1998; 61:662–667.   7. Hurst C, Clark R, Regli S. Estimating the risk of acquiring infectious disease from ingestion of water. In: Hurst C, ed. Modeling disease transmission and its prevention by disinfection. Melbourne: Cambridge University Press; 1996:99–139.   8. Steiner T, Thielman N, Guerrant R. Protozoal agents: what are the dangers for the public water supply? Annu Rev Med 1997; 48:329–340.   9. CDC. Surveillance for waterborne-disease outbreak associated with recreational water – United States, 2003–2004. MMWR 2006; 55(ss-12), 1–22. 10. Joslyn L. Sterilization by heat. In: Block S, ed. Disinfection, sterilization, and preservation. Philadelphia: Lea and Febiger; 1991: 495–527. 11. Frazier W, Westhoff D. Preservation by use of high temperatures. Food ­microbiology. New York: McGraw-Hill; 1978.

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