waterborne disease outbreaks
two or more persons must have experienced a similar illness after exposure to water and be epidemiologically linked by time and by location of exposure to water
classifications of water-related illnesses
waterborne
water-washed
water-based
water-related
waterborne
pathogens that originate in fecal material and are transmitted by ingestion (Cholera)
water-washed
organisms that originate in feces and are transmitted through contact because of inadequate sanitation (shigellosis)
water-based
organisms that originate in the water or spend part of their life cycle in aquatic animals and come in direct contact with human in water or by inhalation (Legionnaire's disease)
water-related
microorganisms with life cycles associated with insects that live or breed in water (malaria)
chemical definition of waterborne disease outbreak
at least one case of illness has occurred as a result of ingestion of water
microbiological definition of waterborne disease outbreak
at least two cases of a disease that have occurred as a result of ingestion of water from a common source
reporting of waterborne disease outbreaks
not mandatory
intensity of investigation varies from state to state and within states
under-reported
many outbreaks are not even recognized
What percentage of US waterborne outbreaks are reported?
10 - 13%
database of disease outbreaks
the CDC and EPA, and the Council of State and Territorial Epidemiologists have maintained a database of disease outbreaks in the U.S. since 1971
database was formulated on the responses to a voluntary reporting by state and local public health officials
trends in waterborne outbreaks - deaths
from 1920-1990, deaths decreased to approximately 1/yr
increased after 1990
reasons for death decrease from 1920 - 1990
improvements in treatment (filtration, chlorination)
improvements in medical care (antibiotics, vaccines)
general improvements in living conditions
trends in waterborne outbreaks
no real decrease since 1920's (possible reasons: fewer outbreaks, but better recognition and reporting; increase in the number of individuals with weakened immune systems)
water systems
community
non-community (transient and non-transient)
individual
community water systems
water supplies serve at least 25 year-round residents or 15 service connections used by year-round residents
non-community water systems
water supplies serve an average of at least 25 individuals for 60 or more days per year
transient non-community water systems (TNCWS)
serve a changing population for a few times in a year (fewer than 25 of the same people over 6 months/year)
examples: parks, campgrounds, highway rest stops
non-transient non-community water systems (NTNCWS):
serve a continuous population (25 or more people for at least 6 months/year) a small proportion of their supply
examples: industries, schools, factories
water source in disease outbreaks
mostly groundwater and wells (72% from 1991 - 1994)
virus outbreaks
waterborne enteric viruses caused 14% of outbreaks and 38% of illnesses in the United States from 1999 to 2002
Milwaukee Cryptosporidium outbreak
March 1993
403,000 ill individuals
4,400 hospitalized individuals
100 deaths (mostly individuals with weakened immune systems)
outbreak recognized when stores ran out of anti-diarrhea medicines
cause not identified for 2 weeks
isolated the oocysts from ice
water met all required standards
Clark County, Nevada Cryptosporidium outbreak
1994
90 people ill
restricted to the AIDS community
10 deaths
lasted 7 months
never isolated the organism in water
water met all required standards
recommendations to prevent waterborne outbreaks & improve surveillance
focus on water system operations, management, water quality, and effective regulations to sustain gains made in the provision of safe drinking water
attention to address and prevent waterborne disease transmission in unregulated drinking water systems
reduce the risk for outbreaks in groundwater systems
understanding of the biology, ecology, and inactivation of Legionella in biofilm and premise plumbing
recognition and focus on premise plumbing and point-of-use issues
additional efforts to reduce the risk of outbreaks associated with drinking water distribution systems
prevention efforts in residential and recreational settings (e.g., campgrounds and parks) to reduce waterborne disease outbreaks
research to better characterize the burden of waterborne disease in the U.S. so that prevention actions can be prioritized and interventions to reduce waterborne disease can be developed
additional resources for outbreak detection and investigation of waterborne disease and outbreaks—including epidemiologic, environmental, and laboratory support—at local, state, territorial, and national levels
routes of exposure to pathogens in water impacted by waste
water --> plants, recreation, aerosols, ingestion, animals
water is applied to a land surface, flows in the subsurface to groundwater, which is used as drinking water
risk assessment
developed by the National Research Council (1983) to address chemical hazards in the environment
the framework was modified to address the associated health effects from environmental exposure to microorganisms
risk assessment methods have been long accepted in the regulatory arena and have been used for the examination of microbiological standards since 1989 and continue to be developed and accepted
process of estimating both the probability that an event will occur and the probable magnitude of its adverse effects over a specified time period
risk
"possibility of experiencing harm from a hazard"
a function of the probability of an adverse health effect and severity of that effect
an inherent property of everyday human existence
a key factor in all decision making on almost all issues
risk assessment process
involves evaluating likelihood/frequency of experiencing a risk
evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors
the information on microbial pathogens or chemicals in the environment is critical in making decisions about potential risks and corrective actions
risk assessment steps
hazard identification (hazard characterization)
exposure assessment (dose-response)
risk characterization
risk analysis steps
risk assessment
risk management
risk communication
microbial risk assessment
hazard identification - What are the contaminants of concern? example: microbial pathogens of concern in stools of infected individuals
exposure assessment - What quantity of the contaminant are we exposed to? example: microorganism Detection in Untreated Wastewater
dose-response assessment - What dose of the organism is required to produce a response in the exposed individual? example: Cryptosporidium infectivity data
risk characterization - What is the probability that an adverse response will occur in the exposed individual? (human illness or death) example: probability of infection for enteric microorganisms
dose response
extrapolated from epidemiologic investigations
obtained by human feeding studies on healthy, young adult volunteers
best estimates based on a limited data base from outbreaks
worst case estimates
cannot be directly used to assess risk because of many variables (see Variables of the Host)
variables of the host
age
general health
pregnancy
medications--OTC or prescription
metabolic disorders
alcoholism, cirrhosis, hemochromatosis
malignancy
amount of food consumed
gastric acidity variation: antacids, natural variation
genetic disturbances
nutritional status
immune competence
surgical history
occupation
available dose-response models - bacteria
Salmonella
Shigella
enteropathogenic E. coli (E. coli 0157-H7 - animals)
Vibrio
Legionella
Campylobacter
Listeria
available dose-response models - viruses
rotavirus
echovirus
coxsackievirus
adenoviruses
available dose-response models - protozoans
Giardia
Cryptosporidium
risk characterization
assumptions in risk calculations for exposure after artificial recharge:
virus inactivation rate: 0.043 log10 /day
vadose zone: 3 m
residence time: 6 months
exposure: 1 liter/day
treatment removal (unchlorinated: 0 log10; chlorinated: 3.9 log10; full: 5.2 log10)
How do we set standards for pathogens?
In 1974 Congress passed Safe Drinking Water Act and EPA established standards for drinking water
standards for chemicals
standards for many contaminants were set using a risk analysis approach
standards for microbes
setting standards was more difficult for microbes because of the detection methods (difficult, costly and days to weeks for results)
therefore, Coliform bacteria was used, but in the 1980s it had become clear that coliform did not indicate the presence of viruses or Giardia, resulting in development of STR and ICR
regulations were established to protect public health, and not to be too troublesome to utilities
Surface Treatment Rule (STR)
developed to ensure the microbial safety of drinking water
requires utilities that use surface waters to provide filtration and enough disinfection to kill viruses
goal of treatment was Giardia infection should not be greater than 1/10,000 (this value is close to the annual risk of infection from waterborne disease outbreaks in U.S. (4/1,000))
went into effect in 1991
required that all drinking water treatment plants be capable of removing 99.9% Giardia & 99.99% viruses
Information Collection Rule (ICR)
developed by the EPA to assess whether the treatment required was enough to ensure 1/10,000 yearly risk
risk management
evaluation of the need for the control of the risk and options for its control
includes consideration of social, political, and economic issues plus the engineering problems inherent in a proposed solution
application of microbial risk assessment
development of standards and criteria
determine needed sensitivity of analytical methods
define treatment requirements
define quantitatively relative risks
evaluate the impact of low level of contamination or chronic exposure
determine cost of subsequent infection, illness and death
cost/benefit analysis
develop standards
define appropriate sampling methodologies
design appropriate treatment strategies
what we have learned from quantitative microbial risk assessment
treatment plant variability in pathogen removal effects long term risk (i.e. 100% removal of all pathogens over time is not possible)
short term exposures can have a significant impact on risk to a community --> the more polluted the raw water source, the greater the need for treatment reliability
greatest Uncertainty in estimating risk is from exposure
no-dose response threshold for enteric viruses and parasites or the infectivity is so low it should be considered one organism
sensitive populations (greatest risk of serious illness and death) represents 20% of U.S. population and is increasing
sequelae are common and have a significant impact on the quality of life
major driving factors
development of molecular methods for detection of pathogens
fingerprinting of microbes
Quantitative Microbial Risk Assessment
increased importation of food products from the developing world
less Tolerance of Risk (Greater public awareness of microbial threats)
changing Demographics (Older population - Increase in immuno-compromised individuals)
changes in Water Supply and Treatment (use of more contaminated sources; treatment process allows greater barrier penetration)
primary standards
based on health considerations
established by the EPA, enforced by states
protect from: toxic chemicals, radioactive elements, pathogens
maximum Contaminant Level (MCL)
secondary standards
for contaminants that cause offensive taste, color, odor, staining, foaming, etc. (do not make people sick)
not enforced
guidelines for treatment plant operators
examples: sulfate, iron & color
Safe Drinking Water Act (SDWA)
passed by Congress in 1974
amended twice in 1986 and 1996
amendments led to announcement of stage 1 & stage 2 Disinfectants & Disinfection Byproducts (DBPs) Rule
EPA has regulated 3 disinfectants and 11 chlorinated by-products at federal level
there are many more unregulated DBPs and some are listed in EPA's candidate contaminant list 5 (CCL5) such as 5 different forms of nitrosamines
Disinfectants & Disinfection Byproducts (DBPs) Rule
established by EPA
aimed to lessen the risk of chlorinated by products
pre-1985 microbial standards
total coliform bacteria concentration: less than or equal to 2.2 per 100 ml
1985 microbial standards
MCLGs established
total coliform bacteria - 0 per 100 mL
viruses - 0
Giardia - 0
Surface Water Treatment Rule (1989)
surface waters must be filtered and disinfected to achieve 99.9% removal (3-log removal) of Giardia and 99.99% removal (4-log removal) of viruses
combined filter effluent (CFE) turbidity 0.5 NTU
Total Coliform Rule (1990)
MCL: 0 per 100 ml
presence-absence test
<5% samples can be positive
repeat samples required for analysis of fecal coliform bacteria
Interim Enhanced (1998) and Long Term 1 E. SWTR (2002)
2-log Cryptosporidium removal/inactivation
CFE 0.3 NTU & individual filter monitoring requirements
Stage 1 DBP Rule
TTHM 80 μg/L and HAA5 60 μg/L
compliance based on system averages
Stage 2 DBP Rule
TTHM 80 μg/L and HAA5 60 μg/L
compliance based on each location
Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) (2006)
up to 2.5-log additional removal/inactivation for filtered systems (compared to STWR, meaning a total of 5.5-log removal)
up to 3-log inactivation for unfiltered systems
3 - 5.5-log Cryptosporidium removal/inactivation based on source concentration and source water monitoring
objective: provide additional protection from pathogens and balance the risks presented by microbial pathogens & DBPs
one of the most recent rules in the M & DBP cluster
cover the reservoir or provide 4-log virus, 3-log Giardia, and 2-log Cryptosporidium removal/inactivation after the reservoir
reduces disease incidence associated with Cryptosporidium and other pathogens in drinking water
supplements SWTR regulations by targeting additional Cryptosporidium treatment requirements to higher risk systems
contains provisions to mitigate risks from uncovered finished water storage facilities and to ensure that systems maintain microbial protection as they take steps to reduce the formation of DBPs
no more system average (every sample must meet DBP concentration and microbial concentrations)
latest and greatest drinking water rule
monitoring requirements
24 months Cryptosporidium monitoring
bin class based on average concentration during monitoring
For all unfiltered systems and small filtered systems (serving <10,000) the average is the mean of all samples
for large filtered systems (serving >10,000), the average differs by the number of samples collected
24 to 47 samples: highest 12 month running annual average
48 samples or higher: mean of all samples
historical data (grandfathered data) that meets QA/QC requirements may be used in lieu of additional monitoring
ground water systems (GWR)
consist of community, non-transient, non-community, and transient, non-community water systems
70-110 million people drink groundwater daily from public supplies in the US
ground water systems implicated in about half of all microbial disease outbreaks
ground water systems have >90% of all coliform MCL violations
microbial contaminants include viruses, bacteria, sometimes protozoa
risk assessments suggest more than 7 million illnesses/year from GW systems
Ground Water Rule
proposed draft rule - July 1992
all public ground water supplies must disinfect
a disinfectant residual must be maintained
disinfection may be avoided if certain criteria are met
GW Rule 2014: requires all public groundwater systems to evaluate their existing disinfection system prior to the first customer to achieve a minimum of 4-log virus inactivation
proposed GWR provisions
periodic sanitary surveys
hydrogeologic sensitivity assessments
source water monitoring (state selects one of the following fecal indicators: E. coli (7 analytical methods), Enterococci (3 analytical methods), or Coliphage (2 analytical methods: 1601 and 1602))
corrective action
compliance monitoring
Ground Water Rule source water monitoring provisions
routine monitoring: system that draws water from "sensitive" aquifer must monitor monthly for at least one year
triggered monitoring: system that has a total coliform-positive sample must collect and analyze 1 source water sample within 24 hrs
MCLGs
Maximum Contaminant Level Goals
established because the present treatment technology is not able to meet the MCLGs but should be able to within a few years
microbial removal
filtration removes lots of bacteria but not lots of viruses
viruses are mostly removed during disinfection
microbes are inactivated/removed during each step of the conventional drinking water treatment process (coagulation, flocculation, sedimentation, filtration, disinfection)
balancing chemical and microbial risks
lowering chlorine concentrations during disinfection is important to reduce disinfection by-product (DBP) formation
decreasing DBP formation can be done by increasing contact time (less chlorine needed for CT value to be met) or using UV light to disinfect
storage tanks are used to increase contact time