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Environmental data assessment for use in public health surveillance.


Public health surveillance is the ongoing systematic collection, analysis, interpretation, and dissemination of data on a health-related event for use in public health action to reduce morbidity and mortality and to improve health (Centers for Disease Control and Prevention [CDC], 2001). Data from a public health surveillance system can be used to guide immediate public health action; for measuring the burden of health-related events including changes in related factors; for identification of populations at high risk; for identification of emerging health concerns; for monitoring of trends; for detection of epidemics and pandemics; for program planning; for implementation and evaluation to prevent and control disease, injury, or adverse exposure; for evaluation of public policy; for detection of changes in health-related practices and the effects of these changes; for prioritization for allocation of resources; for description of health-related events; and for formulation of research hypotheses. In 1997, state or local public health departments conducted public health surveillance on the following environmental health measures: elevated blood lead levels (coordinated on the national level); poisonings (pesticide, mercury, arsenic, cadmium, acute chemical, and carbon monoxide); methemoglobinemia; asthma; heatstroke; and hypothermia (CDC, 1998). Additional public health surveillance efforts are being developed on the national level to measure the impact of the environment on public health (McGeehin, Qualters, & Niskar, 2004).

Total trihalomethane (TTHM) in drinking water is an example of a chemical regulated by the U.S. Environmental Protection Agency (U.S. EPA) but not under public health surveillance. U.S. EPA identifies cancer and liver, kidney, and central-nervous-system problems as potential human health effects from exposure to TTHM levels above 80 [micro]g/L (U.S. EPA, n.d., updated March 1, 2006c). The U.S. EPA database that stores monitoring data for TTHM measures is called the Safe Drinking Water Information System (SDWIS). Specified uses of SDWIS information are for U.S. EPA to oversee state drinking-water programs, track contaminant levels, respond to public inquiries, prepare national reports, evaluate program and regulation effectiveness, and determine if new regulations are needed to protect human health (U.S. EPA, 1999). The objective of this report is to assess SDWIS data on TTHMs, which are an example of environmental data, for public health surveillance according to public health surveillance system attributes: simplicity, flexibility, data quality, acceptability, sensitivity, predictive value positive, representativeness, timeliness, and stability (CDC, 2001).



SDWIS data reporting flows from the laboratory to the utility to the state agency to the U.S. EPA region to SDWIS (American Water Works Association, 1997). Laboratories analyzing TTHM samples for drinking-water compliance are certified by U.S. EPA or the state. TTHM levels in drinking water are defined and reported by states to SDWIS as "yes" (there was a violation of U.S. EPA drinking-water standards) or "no" (there was not a violation). If there is a violation of the standard for TTHM levels in drinking water, the TTHM level is reported by the state to SDWIS. SDWIS defines enforcement actions for noncompliant TTHM levels as "yes" if an enforcement action was conducted by the state. The type of enforcement action varies by state.

The SDWIS definitions of TTHM measures are simple, but the process of collecting, analyzing, and reporting data is complex, with multiple levels of reporting and certifications required for participation (U.S. Environmental Protection Agency, n.d., updated March 1, 2006b; U.S. EPA, n.d., updated June 6, 2006).


In 1974, the Safe Drinking Water Act (amended in 1986 and 1996) authorized U.S. EPA to set drinking-water standards. The agency sets a maximum contaminant level (MCL), defined as the maximum permissible level of a contaminant in water that is delivered to any user or public water system. Exemptions or variances from standards may be granted to public water systems if there is no unreasonable risk to public health. The MCL for TTHMs was set at 100 [micro]g/L in 1978 and lowered to 80 [micro]g/L in 2002 (U.S. EPA, n.d., updated March 1, 2006a; U.S. EPA, n.d., updated March 1, 2006c) Although SDWIS has a history of being flexible and adapting to new information, the complexity of the system means that time is required to implement the changes.

Data Quality

Laboratories participating in SDWIS analyze water samples for TTHMs according to methods approved by U.S. EPA (U.S. EPA, n.d., updated June 6, 2006). Quality control procedures are conducted for SDWIS data management, including uniform data entry guidance. States are required to report noncompliant-finished-water data to SDWIS, but TTHM levels are not reported if the water system is in compliance. The types and impacts of state level enforcement actions are not uniform, and it is not required that they be reported to SDWIS. State level enforcement actions and TTHM violations in public water systems are reported on a quarterly basis. In 1996-1999, 20 percent of water systems reported enforcement actions (n = 1,032 actions). SDWIS state level enforcement action data were 87 percent complete and 83 percent accurate. Time of day and year for water sample collection vary by sampler. Time, location, and weather are factors that affect contaminant levels. Of the SDWIS chemical data violations reported in 1996-1999, including TTHM data, 19 percent of the data were complete and 79 percent accurate. Only 68 percent of violations were reported on time. More than 12 states or territories did not report violations for at least one chemical contaminant (American Water Works Association, 1997; U.S. EPA, 1999; U.S. EPA, 2000; U.S. EPA, n.d., updated February 21, 2006). The quality of laboratory analyses is high. The quality of the data, however, is reduced by variability in data collection and data reporting, delayed reporting, and incomplete data.


The incomplete data and reporting delays described under the heading "Data Quality" suggest that intended participants may lack willingness to participate in SDWIS.


Incomplete data, variability in data collection, and delays in data reporting as described under "Data Quality" suggest that SDWIS may not be detecting all TTHM violations and enforcement actions.

Positive Predictive Value

The quality of SDWIS laboratory analyses as described under the heading "Simplicity" is likely to result in reports of TTHM level violations that are truly violations. In 1996-1999, states over-reported 0.7 percent of public water system violations (U.S. EPA, 2000). As described under "Data Quality," there were discrepancies for approximately one-quarter of the enforcement action data from 1996-1999.


SDWIS covers the specified population/region of more than 172,000 public water systems facilities that serve more than 90 percent of the U.S. population (U.S. Environmental Protection Agency, 1999). The system has demonstrated the ability to describe TTHM events over time, including distribution by place and person across the United States, but representativeness is affected by data quality. Reported TTHM events may not be representative of actual events for the U.S. population since data collection is variable and data reporting is incomplete.


Data on TTHM levels in drinking water and enforcement actions for noncompliant TTHM levels are reported in SDWIS on a quarterly basis. The duration of long-term compliance-monitoring periods varies. A system in which out-of-compliance measurements occur is not considered out of compliance until the monitoring period ends. For example, states would report the monitoring violation within 45 days after the end of the third year of a three-year period. For a quarterly monitoring period, violations identified within the last quarter must be reported within 45 days of the end of the quarter in which the violations have been identified (U.S. EPA, 1999). The speed between steps, particularly from event onset to response, may be timely for the requirements of SDWIS, but SDWIS is not a timely system for identification of real-time potential human exposure to TTHMs.


SDWIS is a stable system that has demonstrated the ongoing ability to produce information and adapt to changes as described under the heading "Flexibility" The reliability and availability of the system for public health surveillance are affected, however, by variability in data collection, reporting delays, and incomplete data.


Data on noncompliant TTHM levels are limited for public health surveillance because the type and impact of enforcement action are not reported to SDWIS. SDWIS has two strengths for measuring TTHMs. First, the violation of a TTHM level is based on a safe-drinking-water standard. Second, U.S. EPA provides uniform protocols for data collection and management, including the U.S. EPA laboratory certification program. The major limitation of SDWIS for measurement of TTHMs is the lack of information on actual levels of TTHMs, which are reported to SDWIS only when the TTHM levels are out of compliance. Ideally, TTHM levels would be recorded in SDWIS when in or out of compliance to serve as an early-warning system to protect human health and to improve the understanding of health-related events.

SDWIS is an example of an existing environmental data system that is potentially useful for public health surveillance. To conduct public health surveillance with environmental data, data owners need to plan for mechanisms to relate environmental and health data in a meaningful and responsible manner that includes thoughtful consideration of time and space factors. The International Health Regulations adopted by the World Health Assembly in May 2005 call for the establishment of a global surveillance system for public health emergencies of international concern, but there is a lack of awareness about limitations and a lack of capabilities to develop and manage systems within the context of the public health surveillance system attributes (Baker & Fidler, 2006). A way of moving beyond these barriers is to increase collaboration among public health and environmental practitioners for the purpose of increasing the role of environmental data in public health surveillance and motivating proactive activities to prevent, detect, and control public health emergencies.

Acknowledgements: The author acknowledges the general support of Gary Rozier, David Moreau, Vaughn Upshaw, Thomas Ricketts, and Andrea Biddle of the University of North Carolina; Paul Garbe of the Centers for Disease Control and Prevention; and Michael McGuire of McGuire Environmental Consultants, Inc.

Corresponding Author: Amanda Sue Niskar, Health Indicator Specialist, Israel Center for Disease Control, Ministry of Health, Gertner Institute, Tel Hashomer, Ramat Gan 52621 Israel. E-mail:


American Water Works Association. (1997). Evaluation of the Environmental Protection Agency's safe drinking water information system (SDWIS). Denver, CO: Author.

Baker, M.G., & Fidler D.P. (2006). Global public health surveillance under new international health regulations. Emerging Infectious Diseases, 12, 1058-1065

Centers for Disease Control and Prevention. (1998). Monitoring environmental disease--United States, 1997. Morbidity and Mortality Weekly Report, 47, 522-525.

Centers for Disease Control and Prevention. (2001). Updated guidelines for evaluating Public health surveillance systems: Recommendations from the guidelines working group. Morbidity and Mortality Weekly Report, 50, 1-35.

McGeehin, M.A., Qualters, J.R., & Niskar, A.S. (2004). National Environmental Public Health Tracking Program: Bridging the information gap. Environmental Health Perspectives, 112, 1409-1413.

U.S. Environmental Protection Agency. (1999). Major findings from the CEIS review of EPA's Safe Drinking Water Information System (SDWIS) database. Washington, DC: Author.

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U.S. Environmental Protection Agency. (n.d., updated March 1, 2006b). Laboratory certification. Retrieved June 17, 2006, from U.S. Environmental Protection Agency. (n.d., updated March 1, 2006c). National primary drinking water standards. Retrieved June 17, 2006, from

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Amanda Sue Niskar, Dr.P.H., M.P.H.
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Title Annotation:Guest Commentary
Author:Niskar, Amanda Sue
Publication:Journal of Environmental Health
Article Type:Author abstract
Date:Nov 1, 2007
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