Carbon Monoxide Exposures --- United States, 2000--2009

Carbon monoxide (CO) poisoning is a leading cause of unintentional poisoning deaths in the United States (1). CO is an odorless, colorless gas that usually remains undetectable until exposure results in injury or death. CO poisoning is preventable; nonetheless, unintentional, non--fire-related CO poisoning is responsible for approximately 15,000 emergency department visits and nearly 500 deaths annually in the United States (2). National estimates of CO exposures have been based on secondary data sources, such as hospital administrative records, and are limited to exposures treated within the health-care system. To describe more completely the national burden of CO exposure and risk factors associated with vulnerable populations, CDC used data from the National Poison Data System (NPDS) to characterize reported unintentional, non--fire-related CO exposures, including those that were managed at the site of exposure and were not treated at a health-care facility. Among 68,316 CO exposures reported to poison centers during 2000--2009, a total of 30,798 (45.1%) were managed at the site of exposure with instructions from the poison center by telephone, 36,691 (53.7%) were treated at a health-care facility, and the management site for the remainder was unknown. Although symptoms varied slightly between persons managed on-site and those treated at a health-care facility, most CO exposures occurred at home and most often involved females, children aged ≤17 years, and adults aged 18--44 years. Surveillance and analysis of data from NPDS and secondary sources might provide a more comprehensive description of the burden of CO exposure in the United States and assist in the development of interventions better targeted to high-risk populations.

NPDS is a near real-time, comprehensive poisoning surveillance system that collects data on calls regarding poison exposure placed to any of the U.S. poison centers. NPDS is owned and managed by the American Association of Poison Control Centers. CDC uses NPDS to receive, analyze, and display data from poison center calls. Calls to poison centers come from health-care professionals or persons voluntarily reporting a poison exposure. The information provided by the caller might pertain to themselves or others and is used by the poison center to create a record of the call with details such as the date, poison substance, and symptoms.* If the report concerns someone who was treated at a health-care facility, a poison center staff member will contact the health-care facility during the course of treatment to obtain pertinent clinical information. Details from poison center records are uploaded to NPDS.

NPDS data from 2000--2009 in which CO was identified in the substance data field and the reason for exposure was recorded as "unintentional" were extracted for this report If "fire" or "smoke" were in the substance data field, these exposures were excluded to restrict the analysis to unintentional, non--fire-related CO exposures. The data were then stratified according to management site (i.e., health-care facility or site of exposure) and a descriptive analysis was conducted. Rates were calculated using reports of CO exposures to the poison centers and 2000--2009 U.S. census data (3,4). Additionally, the characteristics of persons managed on-site were compared with those of persons managed at a health-care facility.

The 68,316 CO exposures reported to poison centers during 2000--2009 represented 0.29% of all poison exposures reported in NPDS. Compared with all exposures reported to NPDS, the proportion of reported CO exposures steadily declined, from 0.31% in 2006 to 0.24% in 2009. On average, 23.2 CO exposures were reported per 1 million population per year (range: 19.7--25.3) (Figure). The number of persons with reported CO exposures who were transported to a health-care facility ranged from 11.1 to 14.3 per million each year and the number of persons with reported CO exposures who were managed on-site ranged from 8.6 to 14.0 per million each year (Figure). Total reported CO exposures included 34,356 females (23.0 per million) and 30,257 males (20.9 per million). The most commonly exposed age groups were <17 years (25.7 per million) and 18--44 years (19.4 per million) (Table 1).

CO exposures most frequently occurred between November and February (53.5%) and among persons residing in the Midwest (31.2 per million) or the Northeast (36.7 per million). A greater proportion of CO exposures managed on-site occurred in the Northeast (35.5%) (Table 1). The exposure site was reported as "residence" (77.6%) or "workplace" (12.0%) in most cases (Table 1). Clinical symptoms were reported for 68.1% of the total exposures, with headache, nausea, and dizziness most commonly reported (Table 2). However, 83.0% of reported exposures had a medical outcome of "no effect" or "minor effect." During 2000--2009, a total of 235 CO exposure--related deaths were reported to NPDS. Of those persons who died, 65.0% were male and 30.5% were aged 18--44 years. Most persons (68.2%) transported to a health-care facility were aged <45 years and 18.6% experienced confusion, syncope, dyspnea, or chest pain following CO exposure. In contrast, among persons managed on-site, 6.2% experienced confusion, syncope, dyspnea, or chest pain (Table 2).

Reported by

Alvin Bronstein, MD, American Association of Poison Control Centers, Alexandria, Virginia. Jacquelyn H. Clower, MPH, Shahed Iqbal, PhD, Fuyuen Y. Yip, PhD, Colleen A. Martin, MSPH, Arthur Chang, MD, Amy F. Wolkin, MSPH, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; Jeneita Bell, MD, EIS Officer, CDC. Corresponding contributor: Jeneita Bell, jbell2@cdc.gov, 770-488-3700.

Editorial Note

NPDS provides national data regarding CO-exposed persons treated at a health-care facility and those who do not seek medical care at a health-care facility. This is the first analysis for which NPDS has been used to examine a 10-year period of reported CO exposures. During 2000--2009, based on reports to NPDS, 30,798 persons were exposed to CO but were not treated at a health-care facility. Those persons would not have been identified through CO exposure data sources that rely on health-care facility records and mortality data. The characteristics of all CO exposures reported in NPDS, including those treated on-site and at a health-care facility, are consistent with previous knowledge of CO exposure (1,2). Women and children are the most commonly exposed, but deaths from CO exposure more often occur among men, and exposures most often occur at home and during winter months. CO exposures in the Northeast more frequently were managed on-site.

From 2006 to 2009, the rate of reported CO exposures steadily declined, and the call proportion declined from 0.31% to 0.24%. Similarly, the proportion of CO exposures among all reported unintentional poison exposures decreased by 0.8% during the period, which might be attributable to an overall reduction in calls to poison centers for any unintentional poisoning. The decrease in CO exposure calls to poison centers also might be a result of factors such as increased use of home CO alarms and improved use and maintenance of portable generators and other CO-emitting devices. Data available through NPDS are limited and insufficient to identify specific factors that might contribute to the observed decline in CO exposure calls. Poison center case notes could provide useful information to identify sources of exposure such as portable generators and furnaces, which are common in unintentional CO poisonings (5).

The findings in this report are subject to at least three limitations. First, not all CO exposures recorded in NPDS are confirmed with biological testing. Each poison expert managing a call uses their own clinical knowledge to determine whether the reported health effects are attributable to the implicated exposure. In some instances, follow-up calls from a poison center to a health-care facility might identify an elevated carboxyhemoglobin level, but this finding would be indicated in case notes, which are not included in the data poison centers submit to NPDS. Second, additional details regarding the cause of exposure, which would be included in case notes and might be useful in understanding risk-behaviors for public health prevention planning, also are omitted from data submitted to NPDS. Finally, the reported exposures represented in this analysis are an underestimate of all CO exposures. Although >20,000 CO exposure-related emergency department visits are reported annually in the United States, NPDS only captured 36,691 of those over a 10-year period (6). Likewise, the number of deaths is an underestimate; previous literature has reported that approximately 450 CO poisoning deaths occur annually in the United States (2). This underestimate exists partly because NPDS is a passive surveillance system and poison center use can vary by geographic location (7). However, CO exposures recorded by NPDS can be used to supplement data from other CO surveillance systems.

Previously, formal characterization of persons exposed to CO only included those who sought treatment at a health-care facility. This left an information gap that could not be addressed with current surveillance methods using hospital administrative records. NPDS can be used to more accurately depict the burden of CO poisoning and its true health impact and cost to society. Using NPDS data, this report found that the demographics of persons managed on-site for CO exposure and those treated at a health-care facility were similar, and the predominant exposure location (e.g., residence) also was similar. This suggests that current prevention efforts for CO poisoning, such as home installation of CO alarms, also can apply to the population managed on-site. NPDS can be useful in monitoring the impact of such prevention efforts. Additionally, state health departments can partner with local poison centers to obtain additional information from case notes to further characterize populations at-risk, determine the circumstances preceding CO exposure, and help develop local- and state-level approaches to prevent CO exposure.

Acknowledgments

Tegan K. Boehmer, PhD, Div of Environmental Hazards and Health Effects, National Center for Environmental Health.

References

1. CDC. Carbon monoxide--related deaths---United States, 1999--2004. MMWR 2007;56:1309--12.
2. CDC. Unitintentional, non--fire-related, carbon monoxide exposures---United States, 2001--2003. MMWR 2005;54:36--9.
3. US Census Bureau. Annual estimates of the resident population for the United States, regions, states, and Puerto Rico: April 1, 2000 to July 1, 2009. Washington, DC: Population Division, US Census Bureau; 2010. Available at http://www.census.gov/popest/states/NST-ann-est.html. Accessed July 29, 2011.
4. US Census Bureau. Annual Estimates of the Resident Population by Sex and Five-Year Age Groups for the United States: April 1, 2000 to July 1, 2009. Washington, DC: Population Division, US Census Bureau; 2010. Available at http://www.census.gov/popest/national/asrh/NC-EST2009-sa.html. Accessed July 29, 2011.
5. Clower JH, Hampson NB, Iqbal S, Yip FY. Recipients of hyperbaric oxygen treatment for carbon monoxide poisoning and exposure circumstances. J Emerg Med. In press 2011.
6. Litovitz T, Benson BE, Youniss J, Metz E. Determinants of U.S. poison center utilization. Clin Toxicol 2010;48:449--57.
7. Iqbal S, Clower JH, Boehmer TK, Yip FY, Garbe P. Carbon monoxide-related hospitalizations in the US: evaluation of a web-based query system for public health surveillance. Public Health Rep 2010;125:423--32.