Association of short-term exposure to ground-level ozone and respiratory outpatient clinic visits in a rural location - Sublette County, Wyoming, 2008-2011.

OBJECTIVE: Short-term exposure to ground-level ozone has been linked to adverse respiratory and other health effects; previous studies typically have focused on summer ground-level ozone in urban areas. During 2008-2011, Sublette County, Wyoming (population: ~10,000 persons), experienced periods of elevated ground-level ozone concentrations during the winter. This study sought to evaluate the association of daily ground-level ozone concentrations and health clinic visits for respiratory disease in this rural county. METHODS: Clinic visits for respiratory disease were ascertained from electronic billing records of the two clinics in Sublette County for January 1, 2008-December 31, 2011. A time-stratified case-crossover design, adjusted for temperature and humidity, was used to investigate associations between ground-level ozone concentrations measured at one station and clinic visits for a respiratory health concern by using an unconstrained distributed lag of 0-3 days and single-day lags of 0 day, 1 day, 2 days, and 3 days. RESULTS: The data set included 12,742 case-days and 43,285 selected control-days. The mean ground-level ozone observed was 47 ± 8 ppb. The unconstrained distributed lag of 0-3 days was consistent with a null association (adjusted odds ratio [aOR]: 1.001; 95% confidence interval [CI]: 0.990-1.012); results for lags 0, 2, and 3 days were consistent with the null. However, the results for lag 1 were indicative of a positive association; for every 10-ppb increase in the 8-h maximum average ground-level ozone, a 3.0% increase in respiratory clinic visits the following day was observed (aOR: 1.031; 95% CI: 0.994-1.069). Season modified the adverse respiratory effects: ground-level ozone was significantly associated with respiratory clinic visits during the winter months. The patterns of results from all sensitivity analyzes were consistent with the a priori model. CONCLUSIONS: The results demonstrate an association of increasing ground-level ozone with an increase in clinic visits for adverse respiratory-related effects in the following day (lag day 1) in Sublette County; the magnitude was strongest during the winter months; this association during the winter months in a rural location warrants further investigation.

A review of disaster-related carbon monoxide poisoning: surveillance, epidemiology, and opportunities for prevention.

OBJECTIVES: We conducted a systematic literature review to better understand aspects of disaster-related carbon monoxide (CO) poisoning surveillance and determine potentially effective prevention strategies. METHODS: This review included information from 28 journal articles on disaster-related CO poisoning cases occurring between 1991 and 2009 in the United States. RESULTS: We identified 362 incidents and 1888 disaster-related CO poisoning cases, including 75 fatalities. Fatalities occurred primarily among persons who were aged 18 years or older (88%) and male (79%). Hispanics and Asians accounted for 20% and 14% of fatal cases and 21% and 7% of nonfatal cases, respectively. Generators were the primary exposure source for 83% of fatal and 54% of nonfatal cases; 67% of these fatal cases were caused by indoor generator placement. Charcoal grills were a major source of exposure during winter storms. Most fatalities (94%) occurred at home. Nearly 89% of fatal and 53% of nonfatal cases occurred within 3 days of disaster onset. CONCLUSIONS: Public health prevention efforts could benefit from emphasizing predisaster risk communication and tailoring interventions for racial, ethnic, and linguistic minorities. These findings highlight the need for surveillance and CO-related information as components of disaster preparedness, response, and prevention.

Recipients of hyperbaric oxygen treatment for carbon monoxide poisoning and exposure circumstances.

BACKGROUND: Unintentional carbon monoxide poisoning is preventable. Severe cases are often referred for hyperbaric oxygen treatment. To guide prevention efforts and treatment practices, this study provides some of the most detailed current information about patients with carbon monoxide poisoning who have been treated at hyperbaric facilities across the United States and the circumstances surrounding their exposures. This study can help improve efforts to prevent carbon monoxide poisoning and enhance treatment practices. METHODS: From August 2008 to January 2010, nonidentifiable, patient-level data were reported by 87 hyperbaric facilities in 39 states via an online reporting system. This reporting system was developed collaboratively by the Undersea and Hyperbaric Medical Society and the Centers for Disease Control and Prevention. RESULTS: Among the 864 patients reported to receive hyperbaric oxygen treatment for unintentional, non-fire-related, carbon monoxide poisoning, most of the patients were white men aged between 18 and 44 years. Only 10% of patients reported the presence of a carbon monoxide alarm at their exposure location, and 75% reported being part of a group exposure. Nineteen patients (2%) reported a prior carbon monoxide exposure. About half (55%) of the patients treated were discharged after treatment; 41% were hospitalized. CONCLUSIONS: The findings in this report expand the knowledge about patients with carbon monoxide poisoning. These results suggest that prevention efforts, such as educating the public about using carbon monoxide alarms and targeting the most at-risk populations, may help reduce the number of exposures, the number of persons with chronic cognitive sequelae, and the resulting burden on the health care system.

Hospital burden of unintentional carbon monoxide poisoning in the United States, 2007.

BACKGROUND: Unintentional, non-fire-related (UNFR) carbon monoxide (CO) poisoning is a leading cause of poisoning in the United States, but the overall hospital burden is unknown. This study presents patient characteristics and the most recent comprehensive national estimates of UNFR CO-related emergency department (ED) visits and hospitalizations. METHODS: Data from the 2007 Nationwide Inpatient and Emergency Department Sample of the Hospitalization Cost and Utilization Project were analyzed. The Council of State and Territorial Epidemiologists' CO poisoning case definition was used to classify confirmed, probable, and suspected cases. RESULTS: In 2007, more than 230,000 ED visits (772 visits/million) and more than 22,000 hospitalizations (75 stays/million) were related to UNFR CO poisoning. Of these, 21,304 ED visits (71 visits/million) and 2302 hospitalizations (8 stays/million) were confirmed cases of UNFR CO poisoning. Among the confirmed cases, the highest ED visit rates were among persons aged 0 to 17 years (76 visits/million) and 18 to 44 years (87 visits/million); the highest hospitalization rate was among persons aged 85 years or older (18 stays/million). Women visited EDs more frequently than men, but men were more likely to be hospitalized. Patients residing in a nonmetropolitan area and in the northeast and midwest regions of the country had higher ED visit and hospitalization rates. Carbon monoxide exposures occurred mostly (>60%) at home. The hospitalization cost for confirmed CO poisonings was more than $26 million. CONCLUSION: Unintentional, non-fire-related CO poisonings pose significant economic and health burden; continuous monitoring and surveillance of CO poisoning are needed to guide prevention efforts. Public health programs should emphasize CO alarm use at home as the main prevention strategy.

Residential carbon monoxide alarm prevalence and ordinance awareness.

OBJECTIVE: Unintentional carbon monoxide (CO) poisoning is a leading cause of poisoning in the United States. Most poisoning cases occur in residential settings and a working CO alarm may prevent many of these events. The use of a CO alarm is mandated in many parts of the country; however, little is known about the compliance and adoption of such ordinances at the population level. This study determined the prevalence of residential CO alarm and awareness of a 2001 CO alarm ordinance in Mecklenburg County, North Carolina in 2009. METHODS: A random sample of households stratified by housing type (eg, single-family homes, multifamily homes) was included in a cross-sectional survey conducted. One adult respondent from each household was administered a questionnaire that included information on sociodemographic and household characteristics, presence of a CO alarm, and CO alarm ordinance awareness. Data were analyzed using multivariate stratified conditional logistic regression. RESULTS: Among 214 participating households (response rate, 23.4%), 145 (67.8%) reported having a working CO alarm and 79 (36.9%) of the respondents were aware of the CO alarm ordinance. Respondents who were aware of the ordinance had 9 times higher odds (95% confidence interval, 3.3-25.9) of having a CO alarm than those who were unaware. Also, households with an attached garage had more than 2 times higher odds (95% confidence interval, 1.0-6.2) of having a CO alarm than those without an attached garage. Awareness of the CO alarm ordinance was not associated with any sociodemographic (eg, age, sex, race, education, income) or household (eg, home ownership, home construction year) characteristics. CONCLUSIONS: Carbon monoxide alarm prevalence in Mecklenburg County households was higher than the national average and was associated with CO alarm ordinance awareness. Public health efforts might benefit from regulations aimed at population-level adoption of preventive health behaviors.

Carbon monoxide-related hospitalizations in the U.S.: evaluation of a web-based query system for public health surveillance.

OBJECTIVE: Carbon monoxide (CO) poisoning is preventable, yet it remains one of the most common causes of poisoning in the U.S. In the absence of a national data reporting system for CO-poisoning surveillance, the burden of CO-related hospitalizations is unknown. Our objective was to generate the first national estimates of CO-related hospitalizations and to evaluate the use of a Web-based query system for public health surveillance. METHODS: The Healthcare Cost and Utilization Project's (HCUP's) 2005 Nationwide Inpatient Sample (NIS) data were used for CO-related hospitalization estimates. Data for confirmed, probable, and suspected cases were generated using the HCUPnet Web-based query system. We used data from 1993 through 2005 NIS to describe trends in CO-related hospitalizations. We used the Centers for Disease Control and Prevention's surveillance evaluation guidelines to evaluate the system. RESULTS: In 2005, there were 24,891 CO-related hospitalizations nationwide: 16.9% (n=4,216) were confirmed, 1.1% (n=279) were probable, and 81.9% (n=20,396) were suspected CO-poisoning cases. Of the confirmed cases (1.42/100,000 population), the highest hospitalization rates occurred among males, older adults (aged > or = 85 years), and Midwestern residents. CO-related hospitalization rates declined from 1993 through 2000 and plateaued from 2001 through 2005. The simplicity, acceptability, sensitivity, and representativeness of the HCUPnet surveillance system were excellent. However, HCUPnet showed limited flexibility and specificity. CONCLUSIONS: Nationwide, the burden of CO exposure resulting in hospitalization is substantial. HCUPnet is a useful surveillance tool that efficiently characterized CO-related hospitalizations for the first time. Public health practitioners can utilize this data source for state-level surveillance.

Hunting with lead: association between blood lead levels and wild game consumption.

BACKGROUND: Wild game hunting is a popular activity in many regions of the United States. Recently, the presence of lead fragments in wild game meat, presumably from the bullets or shot used for hunting, has raised concerns about health risks from meat consumption. OBJECTIVE: This study examined the association between blood lead levels (PbB) and wild game consumption. METHODS: We recruited 742 participants, aged 2-92 years, from six North Dakota cities. Blood lead samples were collected from 736 persons. Information on socio-demographic background, housing, lead exposure source, and types of wild game consumption (i.e., venison, other game such as moose, birds) was also collected. Generalized estimating equations (GEE) were used to determine the association between PbB and wild game consumption. RESULTS: Most participants reported consuming wild game (80.8%) obtained from hunting (98.8%). The geometric mean PbB were 1.27 and 0.84 microg/dl among persons who did and did not consume wild game, respectively. After adjusting for potential confounders, persons who consumed wild game had 0.30 microg/dl (95% confidence interval: 0.16-0.44 microg/dl) higher PbB than persons who did not. For all game types, recent (<1 month) wild game consumption was associated with higher PbB. PbB was also higher among those who consumed a larger serving size (> or = 2 oz vs. <2 oz); however, this association was significant for 'other game' consumption only. CONCLUSIONS: Participants who consumed wild game had higher PbB than those who did not consume wild game. Careful review of butchering practices and monitoring of meat-packing processes may decrease lead exposure from wild game consumption.

Public Perceptions of Environmental Public Health Risks in the United States.

Understanding public perceptions about environmental health hazards, exposures, and health impacts can help environmental public health practitioners to target and prioritize community activities, policy needs, and communication strategies. The online cross-sectional 2013 summer wave of the ConsumerStyles survey sampled U.S. adults and used questions from the Centers for Disease Control's Environmental Public Health Tracking Program to measure public awareness of governmental efforts to track environmental exposures and links to health impacts, as well as perceptions of environmental health issues. Unadjusted and adjusted logistic regressions examined the associations between demographic characteristics and level of awareness of government environmental public health efforts or level of concern about health risks associated with environmental pollutants. Responses were received from 4033 participants, yielding a response rate of 66.0%. More than half of respondents (57.8%) noted concerns about health risks from environmental pollutants. More than one-third (40.0%) of respondents reported awareness of government efforts. Nearly 40% of respondents felt that none of the health impacts listed in the survey were related to environmental issues. Multiple logistic regression models showed that non-Hispanic blacks, other races, females, people with a college or higher education, and people living in the Midwest or South regions were more likely than their counterparts to be concerned about how the environment affects their health. Future work should focus on improving risk communication, filling the information gap on environmental health issues, and understanding how perceptions change over time.

Air Quality Awareness Among U.S. Adults With Respiratory and Heart Disease.

INTRODUCTION: Poor air quality affects respiratory and cardiovascular health. Information about health risks associated with outdoor air quality is communicated to the public using air quality alerts. This study was conducted to assess associations of existing respiratory and heart disease with three aspects of air quality awareness: awareness of air quality alerts, discussing with a health professional strategies to reduce air pollution exposure, and avoiding busy roads to reduce air pollution exposure when walking, biking, or exercising outdoors. METHODS: During 2014-2016, a total of 12,599 U.S. adults participated in summer waves of the ConsumerStyles surveys and self-reported asthma, emphysema/chronic obstructive pulmonary disease, heart disease, and each aspect of air quality awareness. In 2017, associations between each health condition and air quality awareness were estimated using log binomial and multinomial regression. RESULTS: Overall, 49% of respondents were aware of air quality alerts, 3% discussed with a health professional strategies to reduce air pollution exposure, and 27% always/usually avoided busy roads to reduce air pollution exposure. Asthma was associated with increased prevalence of awareness of air quality alerts (prevalence ratio=1.11, 95% CI=1.04, 1.20), discussing with a health professional (prevalence ratio=4.88, 95% CI=3.74, 6.37), and always/usually avoiding busy roads to reduce air pollution exposure (prevalence ratio=1.13, 95% CI=1.01, 1.27). Heart disease was not associated with air quality awareness. CONCLUSIONS: Existing respiratory disease, but not heart disease, was associated with increased air quality awareness. These findings reveal important opportunities to raise awareness of air quality alerts and behavior changes aimed at reducing air pollution exposure among adults at risk of exacerbating respiratory and heart diseases.

Air pollution-associated changes in lung function among asthmatic children in Detroit.

In a longitudinal cohort study of primary-school-age children with asthma in Detroit, Michigan, we examined relationships between lung function and ambient levels of particulate matter < or = 10 microm and < or = 2.5 microm in diameter (PM10 and PM2.5) and ozone at varying lag intervals using generalized estimating equations. Models considered effect modification by maintenance corticosteroid (CS) use and by the presence of an upper respiratory infection (URI) as recorded in a daily diary among 86 children who participated in six 2-week seasonal assessments from winter 2001 through spring 2002. Participants were predominantly African American from families with low income, and > 75% were categorized as having persistent asthma. In both single-pollutant and two-pollutant models, many regressions demonstrated associations between higher exposure to ambient pollutants and poorer lung function (increased diurnal variability and decreased lowest daily values for forced expiratory volume in 1 sec) among children using CSs but not among those not using CSs, and among children reporting URI symptoms but not among those who did not report URIs. Our findings suggest that levels of air pollutants in Detroit, which are above the current National Ambient Air Quality Standards, adversely affect lung function of susceptible asthmatic children.

Assessment of personal and community-level exposures to particulate matter among children with asthma in Detroit, Michigan, as part of Community Action Against Asthma (CAAA).

We report on the research conducted by the Community Action Against Asthma (CAAA) in Detroit, Michigan, to evaluate personal and community-level exposures to particulate matter (PM) among children with asthma living in an urban environment. CAAA is a community-based participatory research collaboration among academia, health agencies, and community-based organizations. CAAA investigates the effects of environmental exposures on the residents of Detroit through a participatory process that engages participants from the affected communities in all aspects of the design and conduct of the research; disseminates the results to all parties involved; and uses the research results to design, in collaboration with all partners, interventions to reduce the identified environmental exposures. The CAAA PM exposure assessment includes four seasonal measurement campaigns each year that are conducted for a 2-week duration each season. In each seasonal measurement period, daily ambient measurements of PM2.5 and PM10 (particulate matter with a mass median aerodynamic diameter less than 2.5 microm and 10 microm, respectively) are collected at two elementary schools in the eastside and southwest communities of Detroit. Concurrently, indoor measurements of PM2.5 and PM10 are made at the schools as well as inside the homes of a subset of 20 children with asthma. Daily personal exposure measurements of PM10 are also collected for these 20 children with asthma. Results from the first five seasonal assessment periods reveal that mean personal PM10 (68.4 39.2 microg/m(3)) and indoor home PM10 (52.2 30.6 microg/m(3)) exposures are significantly greater (p < 0.05) than the outdoor PM10 concentrations (25.8 11.8 microg/m(3)). The same was also found for PM2.5 (indoor PM2.5 = 34.4 21.7 microg/m(3); outdoor PM2.5 = 15.6 8.2 microg/m(3)). In addition, significant differences (p < 0.05) in community-level exposure to both PM10 and PM2.5 are observed between the two Detroit communities (southwest PM10 = 28.9 14.4 microg/m(3)), PM2.5 = 17.0 9.3 microg/m(3); eastside PM10 = 23.8 12.1 microg/m(3), PM2.5 = 15.5 9.0 microg/m(3). The increased levels in the southwest Detroit community are likely due to the proximity to heavy industrial pollutant point sources and interstate motorways. Trace element characterization of filter samples collected over the 2-year period will allow a more complete assessment of the PM components. When combined with other project measures, including concurrent seasonal twice-daily peak expiratory flow and forced expiratory volume at 1 sec and daily asthma symptom and medication dairies for 300 children with asthma living in the two Detroit communities, these data will allow not only investigations into the sources of PM in the Detroit airshed with regard to PM exposure assessment but also the role of air pollutants in exacerbation of childhood asthma.

Residential traffic exposure and childhood leukemia: a systematic review and meta-analysis.

CONTEXT: Exposure to elevated concentrations of traffic-related air pollutants in the near-road environment is associated with numerous adverse human health effects, including childhood cancer, which has been increasing since 1975. Results of individual epidemiologic studies have been inconsistent. Therefore, a meta-analysis was performed to examine the association between residential traffic exposure and childhood cancer. EVIDENCE ACQUISITION: Studies published between January 1980 and July 2011 were retrieved from a systematic search of 18 bibliographic databases. Nine studies meeting the inclusion criteria were identified. Weighted summary ORs were calculated using a random effects model for outcomes with four or more studies. Subgroup and sensitivity analyses were performed. EVIDENCE SYNTHESIS: Childhood leukemia was positively associated (summary OR=1.53, 95% CI=1.12, 2.10) with residential traffic exposure among seven studies using a postnatal exposure window (e.g., childhood period or diagnosis address) and there was no association (summary OR=0.92, 95% CI=0.78, 1.09) among four studies using a prenatal exposure window (e.g., pregnancy period or birth address). There were too few studies to analyze other childhood cancer outcomes. CONCLUSIONS: Current evidence suggests that childhood leukemia is associated with residential traffic exposure during the postnatal period, but not during the prenatal period. Additional well-designed epidemiologic studies that use complete residential history to estimate traffic exposure, examine leukemia subtypes, and control for potential confounding factors are needed to confirm these findings. As many people reside near busy roads, especially in urban areas, precautionary public health messages and interventions designed to reduce population exposure to traffic might be warranted.

Residential proximity to major highways - United States, 2010.

Traffic-related air pollution is a main contributor to unhealthy ambient air quality, particularly in urban areas with high traffic volume. Within urban areas, traffic is a major source of local variability in air pollution levels, with the highest concentrations and risk of exposure occurring near roads. Motor vehicle emissions represent a complex mixture of criteria air pollutants, including carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM), as well as hydrocarbons that react with NOx and sunlight to form ground-level ozone. Individually, each of these pollutants is a known or suspected cause of adverse health effects. Taking into consideration the entire body of evidence on primary traffic emissions, a recent review determined that there is sufficient evidence of a causal association between exposure to traffic-related air pollution and asthma exacerbation and suggestive evidence of a causal association for onset of childhood asthma, nonasthma respiratory symptoms, impaired lung function, all-cause mortality, cardiovascular mortality, and cardiovascular morbidity.

Air pollution and respiratory symptoms among children with asthma: vulnerability by corticosteroid use and residence area.

RATIONALE: Information on how ambient air pollution affects susceptible populations is needed to ensure protective air quality standards. OBJECTIVES: To estimate the effect of community-level ambient particulate matter (PM) and ozone (O) on respiratory symptoms among primarily African-American and Latino, lower-income asthmatic children living in Detroit, Michigan and to evaluate factors associated with heterogeneity in observed health effects. METHODS: A cohort of 298 children with asthma was studied prospectively from 1999 to 2002. For 14days each season over 11 seasons, children completed a respiratory symptom diary. Simultaneously, ambient pollutant concentrations were measured at two community-level monitoring sites. Logistic regression models using generalized estimating equations were fit for each respiratory symptom in single pollutant models, looking for interactions by area or by corticosteroid use, a marker of more severe asthma. Exposures of interest were: daily concentrations of PM<10µm, <2.5µm, and between 10 and 2.5µm in aerodynamic diameter (PM, PM, and PM respectively), the daily 8-hour maximum concentration of O (8HrPeak), and the daily 1-hour maximum concentration of O (1HrPeak). RESULTS: Outdoor PM, PM, 8HrPeak, and 1HrPeak O concentrations were associated with increased odds of respiratory symptoms, particularly among children using corticosteroid medication and among children living in the southwest community of Detroit. Similar patterns of associations were not seen with PM. CONCLUSIONS: PM and O at levels near or below annual standard levels are associated with negative health impact in this population of asthmatic children. Variation in effects within the city of Detroit and among the subgroup using steroids emphasizes the importance of spatially refined exposure assessment and the need for further studies to elucidate mechanisms and effective risk reduction interventions.

National carbon monoxide poisoning surveillance framework and recent estimates.

OBJECTIVES: Unintentional, non-fire-related (UNFR) carbon monoxide (CO) poisoning is a leading cause of poisoning in the United States. A comprehensive national CO poisoning surveillance framework is needed to obtain accurate estimates of CO poisoning burden and guide prevention efforts. This article describes the current national CO poisoning surveillance framework and reports the most recent national estimates. METHODS: We analyzed mortality data from the National Vital Statistics System multiple cause-of-death file, emergency department (ED) and hospitalization data from the Healthcare Cost and Utilization Project's Nationwide Emergency Department Sample and Nationwide Inpatient Sample, hyperbaric oxygen treatment (HBOT) data from HBOT facilities, exposure data from the National Poison Data System, and CO alarm prevalence data from the American Housing Survey and the National Health Interview Survey. RESULTS: In the United States, 2,631 UNFR CO deaths occurred from 1999 to 2004, an average of 439 deaths annually. In 2007, there were 21,304 (71 per one million population) ED visits and 2,302 (eight per one million population) hospitalizations for confirmed cases of CO poisoning. In 2009, 552 patients received HBOT, and from 2000 to 2009, 68,316 UNFR CO exposures were reported to poison centers. Most nonfatal poisonings were among children (<18 years of age) and females; hospitalizations and deaths occurred more frequently among males and elderly people (>65 years of age). More poisonings occurred during winter months and in the Midwest and Northeast. CONCLUSIONS: UNFR CO poisoning poses a significant public health burden. Systematic evaluation of data sources coupled with modification and expansion of the surveillance framework might assist in developing effective prevention strategies.

The impact of excess heat events in Maricopa County, Arizona: 2000--2005.

Exposure to excess heat is preventable yet it is the primary weather-related cause of mortality in the United States. In the Southwest United States, high temperatures are common and indoor environments often have cooling devices. In summer 2005, Maricopa County, Arizona experienced a 182% increase in reported heat-related deaths in comparison to 2000--2004. We examined at-risk populations and excess mortality. We characterized heat-related deaths using descriptive and multivariate time-series analyses of county vital record data from June-September 2000--2005. Dose-response relationships for heat-related mortality and heat index were evaluated using linear and quadratic splines. From June-September, 2000--2005, 136 heat-related deaths (0.68 per 100,000) were reported; 49 (36%) occurred in 2005. In July 2005, a 14-day heat wave resulted in 28 (57%) reported deaths--a 102% increase in comparison to the same time period in 2000--2004. Decedent demographics in 2005 did not differ from previous years. The mean age of all 136 deaths was 56 years (range: 7-92 years). Of those with discernable reported injury locations, 62 (66%) were identified outdoors. Forty-eight (77%) decedents identified outdoors were < 5 years; conversely, 26 (82%) decedents who were found indoors were > or = 65 years. A 6% (95% CI: 1.00-1.13) increase in mortality risk was observed for each degree (F) increase in heat index. Excess heat impacted a younger population in Maricopa County and many deaths occurred outdoors. Consecutive days of heat exposure--even among a heat-acclimated population--can increase mortality risk. Public health response activities guided by locally obtained data will better target those at risk.

Measles outbreak epidemiology in the United States, 1993-2001.

To evaluate the extent of measles virus circulation and populations at risk in the United States, we reviewed measles outbreaks during 1993-2001. A total of 120 measles outbreaks, constituting 1804 outbreak-related cases, were reported during this period. The maximum outbreak size decreased from 233 cases in 1993-1995 to 119 cases in 1996-1998 and 15 cases in 1999-2001. The maximum outbreak duration decreased from 127 days in 1993-1995 to 65 days in 1999-2001. The majority of outbreaks resulted from documented spread from an internationally imported case (42%) or had a strain of measles virus not endemic in the United States (12%). Outbreaks in which adults were the predominant age group affected accounted for 35% of all outbreaks, compared with 29% of outbreaks predominantly affecting preschool children, 30% predominantly affecting school-aged children and adolescents, and 6% with no predominant age group. The extremely limited size and duration of measles outbreaks indicates very high population immunity to measles and suggests that measles is no longer endemic in the United States.