Question

What historical events led to the discovery of water-borne pathogens?

(b) What municipal drinking water disinfection method led to significant reductions in water-borne pathogenic diseases in cities?

(c) What is the main disadvantage of the disinfection method listed in part (b)?

Answer 1

a) Historical events led to the discovery of water-borne pathogens

The Waterborne Disease and Outbreak Surveillance System (WBDOSS) has tracked water-borne disease outbreaks since the 1970s. The system collects information on when and where the outbreak occurred, the source of contamination, the agent(s) that caused the illness, the number of people who got sick, and the demographic characteristics and symptoms documented on standardized forms. These data have been routinely reported and informs the development of Drinking Water Regulations and Recreational Water Regulations.

1920s

• Waterborne disease reporting began in the United States. Some health departments tracked outbreaks before that time.

1970-1979

1971

• CDC, EPA, and CSTE launch the national Waterborne Disease and Outbreak Surveillance System (WBDOSS).
• Foodborne and waterborne disease outbreaks reported to the same surveillance system.
• Waterborne outbreak defined as two or more cases epidemiologically linked to consumption of water from municipal, semi-public, or individual drinking water systems.
• Individual water system defined as wells or springs used exclusively by single residences in areas without municipal systems.

1974

• Added single cases of chemical poisoning (when public health investigation indicated that drinking water was contaminated by a chemical).
• First record of recreational water-associated Pontiac fever involving exposure to a whirlpool.

1976

• Redefined individual water systems as wells or springs used by single or several residences or by persons traveling outside populated areas (for example, backpackers).

1978

• Recreational waterborne outbreaks added, which included infections or intoxications but excluded wound infections.
• Foodborne and waterborne outbreaks moved to separate surveillance systems and started reporting separately.

1979

• Redefined drinking water systems as community systems, noncommunity systems, and individual systems (1976 definition for individual system)

1980-1989

• 1980

• First record of Pseudomonas dermatitis related to whirlpools (hot tub infection)

1981

• Defined recreational water outbreaks as illnesses due to exposure or unintentional ingestion of fresh or marine water (excluded wound infections).

1988

• MMWR publishes first outbreak surveillance summary on June 1, 1988
• First reported outbreak of Cryptosporidium associated with recreational water.

1989

• Redefined total number of cases to exclude secondary cases
• Added single cases of lab-confirmed primary amebic meningoencephalitis
• Redefined recreational water outbreaks to include illnesses due to inhalation of contaminated water
• Added outbreaks of Pontiac fever associated with whirlpools (excluded outbreaks of Legionnaires’ disease)

1990-1999

1991

• Excluded outbreaks caused by contamination of water or ice at point-of-use. These were categorized as foodborne outbreaks
• Redefined recreational water outbreaks to include outbreaks in swimming pools and whirlpools (beyond whirlpool/hot tub dermatitis)

1995

• Prioritized using the estimated case count instead of the actual case count when the study population was randomly sampled or the estimated count was calculated using the attack rate

1999

• Added outbreaks associated with occupational uses of water
• Redefined individual water systems to include water not intended for drinking and bottled water
• Redefined recreational water outbreak to include outbreaks in wading pools and interactive fountains

2000-2009

2001

• CDC launched the Healthy Swimming Program
• Published drinking and recreational water outbreak surveillance summaries separately
• Redefined recreational water outbreak to specify that the epidemiologic evidence must implicate either recreational water or the recreational water setting as the probable source of illness
• Added recreational water air quality events and single cases of recreational water-associated wound infections
• Added Legionnaires’ disease outbreaks. Previously, only Pontiac fever outbreaks were included

2003

• Redefined deficiency classification to include additional categories that capture waterborne outbreaks due to point-of-use contamination (except ice contamination)
• Revised definition of etiologic agent to list multiple etiologies when each agent individually represented > 5% of positive specimens
• Redefined illness types to list all types if more than 50% of cases reported a symptom in that category

2005

• Expanded the deficiency classifications for drinking water to include deficiency 13 (Treatment process not expected to remove a chemical contaminant)
• Analyzed single cases of illness (e.g., Naegleria fowleri, Vibrio, and chemicals for recreational water, and bottled water for drinking water) separately from waterborne outbreaks.

2006

• EPA used surveillance summary data to support development of the 2006 Ground Water Rule (GWR)

2007

• CDC launched the Model Aquatic Health Code initiative based on data from outbreak surveillance
• Revised the criteria used to determine the strength-of-evidence classifications to include molecular epidemiology along with traditional epidemiology
• Added data from legionellosis outbreaks that occurred prior to 2001

2009

• Implemented electronic outbreak reporting through the National Outbreak Reporting System (NORS). This replaced paper-based outbreak reporting conducted since 1971.
• Created the “Other Non-recreational Water” category to replace two previously reported categories: “Water Not Intended for Drinking” and “Water of Unknown Intent.” This category includes outbreaks not associated with public or private drinking water systems, as well as outbreaks for which the intended use of the water is not known. The category does not include outbreaks associated with recreational water venues (e.g., swimming pools), which are reported separately.
• Assigned multiple deficiency categories to Legionella outbreaks for the first time, to better describe factors contributing to these outbreaks
• For the first time, the majority of outbreaks associated with drinking water systems were caused by Legionella.

b) Municipal drinking water disinfection method led to significant reductions in water-borne pathogenic diseases in cities

The goal of disinfection of public water supplies is the elimination of the pathogens that are responsible for waterborne diseases. The transmission of diseases such as typhoid and paratyphoid fevers, cholera, salmonellosis, and shigellosis can be controlled with treatments that substantially reduce the total number of viable microorganisms in the water.

While the concentration of organisms in drinking water after effective disinfection may be exceedingly small, sterilization (i.e., killing all the microbes present) is not attempted. Sterilization is not only impractical, it cannot be maintained in the distribution system. Assessment of the reduction in microbes that is sufficient to protect against the transmission of pathogens in water is discussed below.

Chlorination is the most widely used method for disinfecting water supplies in the United States. The near universal adoption of this method can be attributed to its convenience and to its highly satisfactory performance as a disinfectant, which has been established by decades of use. It has been so successful that freedom from epidemics of waterborne diseases is now virtually taken for granted. As stated in Drinking Water and Health (National Academy of Sciences, 1977), "chlorination is the standard of disinfection against which others are compared."

However, the discovery that chlorination can result in the formation of trihalomethanes (THM's) and other halogenated hydrocarbons has prompted the reexamination of available disinfection methodology to determine alternative agents or procedures .

The method of choice for disinfecting water for human consumption depends on a variety of factors. These include:

• its efficacy against waterborne pathogens (bacteria, viruses, protozoa, and helminths);
• the accuracy with which the process can be monitored and controlled;
• its ability to produce a residual that provides an added measure of protection against possible posttreatment contamination resulting from faults in the distribution system;
• the aesthetic quality of the treated water; and
• the availability of the technology for the adoption of the method on the scale that is required for public water supplies.

Economic factors will also play a part in the final decision; however, this study is confined to a discussion of the five factors listed above as they apply to various disinfectants.

C) The main disadvantage

Free Chlorine (HOCl and OCl-)

Butterfield et al. (1943) studied percentages of inactivation as functions of time for E. coli, Enterobacter aerogenes, Pseudomonas aeruginosa, Salmonella typhi, and Shigella dysenteriae. They used different levels of free chlorine at pH values ranging from 7.0 to 10.7 and two temperature ranges—2°C to 5°C and 20°C to 25°C. Their work is of great importance, since very few other studies have been conducted that dealt with the action of disinfectants on pathogens. Generally, they found that the primary factors governing the bactericidal efficacy of free available chlorine and combined available chlorine were:

• the time of contact between the bacteria and the bactericidal agent, i.e., the longer the time, the more effective the chlorine disinfection process;
• the temperature of the water in which contact is made, i.e., the lower the temperature, the less effective the chlorine disinfecting activity; and
• the pH of the water in which contact is made, i.e., the higher the pH, the less effective chlorination.

Thus, the test bacteria will be killed more rapidly at lower pH values and at higher temperatures. Since hypochlorous acid would predominate at lower pH's (Figure II-1), the data of Butterfield et al. show that it is a better bactericide than the hypochlorite ion. For example, to produce a 100% inactivation of an initial inoculum of 8 × 105 E. coli in 400 ml of sterile chlorine demand-free water (2,000/ml) at 20°C-25°C with a chlorine level of 0.046 to 0.055 mg/liter, 1.0 min was required at pH 7.0, but at pH 8.5, 9.8, and 10.7, between 20 and 60 min of exposure were needed. At higher concentrations of chlorine, i.e., from 0.1 to 0.29 mg/liter, exposure of 1.0 min was required at pH 7.0, 10 min at pH 8.5, 20 min at 9.8, and 60 min at 10.7. A similar pH effect was noted for S. typhi.