2 tables omitted
Carbon monoxide (CO) is a colorless, odorless, poisonous gas that results
from incomplete combustion of fuels (e.g., natural or liquefied petroleum
gas, oil, wood, coal, or other fuels). CO sources (e.g., furnaces, generators,
gas heaters, and motor vehicles) are common in homes or work environments
and can put persons at risk for CO exposure and poisoning. Most signs and
symptoms of CO exposure are nonspecific (e.g., headache or nausea) and can
be mistakenly attributed to other causes, such as viral illnesses. Undetected
or unsuspected CO exposure can result in death.1 To
examine fatal and nonfatal unintentional, non–fire-related CO exposures,
CDC analyzed 2001-2003 data on emergency department (ED) visits from the National
Electronic Injury Surveillance System All Injury Program (NEISS-AIP) and 2001-2002
death certificate data from the National Vital Statistics System (NVSS). During
2001-2003, an estimated 15,200 persons with confirmed or possible non–fire-related
CO exposure were treated annually in hospital EDs. In addition, during 2001-2002,
an average of 480 persons died annually from non–fire-related CO poisoning.
Although males and females were equally likely to visit an ED for CO exposure,
males were 2.3 times more likely to die from CO poisoning. Most (64%) of the
nonfatal CO exposures occurred in homes. Efforts are needed to educate the
public about preventing CO exposure.
NEISS-AIP is operated by the U.S. Consumer Product Safety Commission
and collects data regarding initial ED visits for all types and causes of
injuries.2 Data are drawn from a nationally
representative subsample of 66 of 100 NEISS hospitals that were selected as
a stratified probability sample of hospitals in the United States and its
territories. NEISS-AIP provides data on approximately 500,000 injury-related
and consumer-product–related ED cases each year.
Nonfatal cases were defined as those recorded at an NEISS-AIP hospital
as CO exposure or CO poisoning. An incident was identified as a case if (1)
the intent of injury was unintentional or undetermined, (2) the principal
diagnosis by a physician was “poisoning” or “anoxia,”
and (3) the consumer product indicated was “CO detector” or “CO
poisoning (source unknown)” or a brief narrative abstracted from the
medical record indicated either CO exposure or CO poisoning. Fire-related
(i.e., burn and smoke inhalation) cases were excluded. In addition, because
death data are not captured completely by NEISS-AIP, persons who were dead
on arrival or who died in the ED also were excluded. Data for all cases were
reviewed independently by two CDC epidemiologists to confirm they met the
case criteria. Narratives were also reviewed to determine CO source, exposure
status (on the basis of physician diagnosis), and symptoms reported.
Each case was assigned a sample weight on the basis of the inverse of
the probability of selection; these weights were summed to provide national
estimates of nonfatal CO exposures. Estimates were based on weighted data
for 778 patients with confirmed or possible CO exposure treated at NEISS-AIP
hospital EDs during 2001-2003. Three years of data were necessary to provide
stable rates. Confidence intervals (CIs) were calculated by using a direct
variance estimation procedure that accounted for the sample weights and complex
sample design. Because CO source and symptoms were undetermined for a high
percentage of cases, data on these factors were based on unweighted data for
NEISS-AIP cases and thus are not nationally representative.
Death certificate data were obtained from NVSS.3 Using
multiple-cause-of-death files from the National Center for Health Statistics
(NCHS),3 CO poisoning deaths were defined as
those with any mention on the death certificate of International
Classification of Diseases, Tenth Revision (ICD-10) code T58 (“Toxic
effect of carbon monoxide”) as a leading or contributing cause of death
and an ICD-10 underlying-cause-of-death code of X47 (“Accidental poisoning
by and exposure to other gases or vapors”) or Y17 (“Poisoning
by and exposure to other gases or vapors, undetermined intent”). NVSS
is a complete census of all deaths and therefore is not subject to sampling
error; however, CIs were calculated to account for random error.3 The
case-fatality rate (CFR) was calculated as the number of CO deaths divided
by the sum of CO deaths and nonfatal CO exposures multiplied by 100. Rates
were calculated by using 2001-2003 U.S. census bridged-race population estimates
During 2001-2003, an estimated 15,200 persons were treated annually
in EDs for nonfatal, unintentional, non–fire-related CO exposure, and,
during 2001-2002, an average of 480 persons died each year from unintentional,
non–fire-related CO exposure. The nonfatal rate for CO exposure was
highest for children aged ≤4 years (8.2 per 100,000 population), whereas
the CO death rate was highest for adults aged ≥65 years (0.32). Adults
aged ≥65 years accounted for 23.5% of CO poisoning deaths. The nonfatal
rate was similar for males and females; in contrast, the death rate for males
was 2.7 times that for females. The CFR increased with age, from 0.6% for
children aged ≤4 years to 5.5% for adults aged 55-64 years; also, the CFR
for males was 2.3 times that for females. The death rate was highest for non-Hispanic
whites and blacks (0.17 per 100,000). Eleven percent of those treated in EDs
were either hospitalized or transferred to another hospital for specialized
The annualized incidence of fatal and nonfatal CO exposures occurred
more often during the fall and winter months, with the highest numbers occurring
during December (56 fatal and 2,157 nonfatal exposures) and January (69 fatal
and 2,511 nonfatal exposures). The annualized incidence was substantially
lower during the summer months, with 21 fatal and 510 nonfatal exposures occurring
during June and 22 fatal and 524 nonfatal exposures occurring during July.
The majority (64.3%) of nonfatal CO exposures were reported to occur
in homes; 21.4% occurred in public facilities and areas. Narratives abstracted
from the medical records of NEISS-AIP cases indicated that 18.5% of CO exposure
incidents were associated with faulty furnaces. An additional 9% were associated
with motor vehicles. CO poisonings were diagnosed in approximately half of
the NEISS-AIP cases, of which 73% had symptoms noted in the medical record.
The most common symptoms experienced were headache (37.5%), dizziness (18.0%),
and nausea (17.3%). Severer symptoms were reported less often, including loss
of consciousness (7.7%), shortness of breath (6.7%), and loss of muscle control
(3.5%). According to medical records, 9.3% of patients in the NEISS-AIP sample
reported that they had a CO detector at home, and 100% of those indicated
that the detector had alerted them to the presence of CO.
M Vajani, MPH, JL Annest, PhD, Office of Statistics and Programming;
M Ballesteros, PhD, J Gilchrist, MD, Div of Unintentional Injury Prevention,
National Center for Injury Prevention and Control; A Stock, PhD, Div of Environmental
Hazards and Health Effects, National Center for Environmental Health, CDC.
Data in this report indicate that, each year, approximately 15,000 U.S.
residents visit EDs for unintentional, non–fire-related CO exposure
and approximately 500 die from unintentional, non–fire-related CO poisoning.
Primary CO sources were home appliances, and the majority of exposures occurred
during the fall and winter months, when persons are more likely to use gas
furnaces and heaters. During warmer months, boating activities might also
be a source of exposure.5 This analysis also
determined that males are more likely to die from CO poisoning than females,
which is consistent with previous findings.6- 8 Males
might be exposed to higher CO levels during high-risk activities, such as
working indoors or in enclosed garages with combustion-engine–driven
tools (e.g., generators or power washers).7 The
CO poisoning death rate was highest among persons aged ≥65 years, likely
attributable to their being at higher risk for undetected CO exposure because
symptoms often resemble those associated with other health conditions common
among older persons.9
The findings in this report are subject to at least three limitations.
First, data on sources of CO exposure and symptoms of persons with CO poisoning
were missing for a substantial percentage of cases. Second, national estimates
of nonfatal injuries are based solely on persons treated in EDs and do not
include those treated in outpatient settings or not treated at all. Finally,
although risks for CO exposure vary by state and locality (e.g., because of
differences in winter weather conditions), NEISS-AIP provides only national
estimates and not state or local estimates.
Primary prevention of residential CO exposure can be accomplished through
simple precautions (Box).
Although residential CO detectors are important for early detection of CO,
they should be considered a secondary prevention method. High oil and gas
prices and power outages during winter months can contribute to consumer use
of improperly vented heating sources. Public education campaigns, especially
during winter months, combined with provision of battery-operated CO detectors
for low-income persons, might reduce CO poisonings.10 Previous
studies also suggest a need for multilingual educational campaigns to reach
Graphic Jump Location
This report is based on data contributed by T Schroeder, MS, C Irish,
and other staff members, Div of Hazard and Injury Data Systems, US Consumer
Product Safety Commission.
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