Design and rationale of the atrial fibrillation occurring transiently with stress (AFOTS) incidence study.

BACKGROUND: Atrial fibrillation (AF) is often detected for the first time in patients hospitalized for medical illness or non-cardiovascular surgery. AF occurring transiently with stress (AFOTS) describes this manifestation of AF, which may either be the result of a non-cardiac stressor, or existing paroxysmal AF that was not previously detected. Current estimates of AFOTS incidence are imprecise: ranging from 1 to 44%, owing to the marked heterogeneity in patient populations, identification and methods used to detect AFOTS. METHODS: The prospective, two-centre epidemiological AFOTS Incidence study will enroll 250 consecutive participants without a history of AF but with at increased risk of AF (Age ≥ 65 or >50 with one risk factor for AF) admitted to intensive care units (ICUs) for medical illness or non-cardiac surgery. Upon admission, participants will wear an ECG patch monitor that will remain in place for 14 days, or until discharge from hospital. Patients' consent to participation is deferred for up to 72 h after admission. The primary endpoint is the incidence of AF lasting ≥30 s. The study is powered to detect an AF incidence of 17% ±â€¯5%. RESULTS: We conducted a vanguard feasibility study, and 55 participants have completed participation. The median duration of monitoring was seven days. AF was detected by the clinical team in 8 participants (14%; 95% Confidence Interval 7-26%). CONCLUSIONS: The AFOTS Incidence study will employ a systematic and highly sensitive protocol for detecting AFOTS in medical illness and non-cardiac surgery ICU patients. This study is feasible and will provide a reliable estimate of the true incidence of AFOTS in this population.

Association between exposure to household cigarette smoking behavior and cigarette smoking in Hispanic adults: Findings from the Hispanic Community Health Study/Study of Latinos.

BACKGROUND: Cigarette smoking behavior is highly determined by social influences during childhood and adolescence. This phenomenon has not been fully evaluated in the Hispanic/Latino population. PURPOSE: To examine the association between exposure to household cigarette smoking behavior (HCSB) and adult cigarette smoking among a diverse Hispanic/Latino population living in four US urban centers. The effect of acculturation on cigarette smoking was also evaluated. METHODS: Data from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) (n=13,231, ages 18-74years, collected between March 2008 and June 2011) were analyzed using logistic regression. RESULTS: HCSB exposure was an independent risk factor for adult current cigarette smoking in Hispanic/Latinos (OR 1.7; 95% CI 1.4, 2.1) after controlling for relevant confounders including socio-demographic and cultural factors. Cubans and Puerto Ricans had the highest prevalence of HCSB exposure (59% and 47% respectively) and highest prevalence of current cigarette smoking (26% and 32%) compared with other Hispanic/Latino groups, (p<.01). CONCLUSIONS: Our data suggest that exposure to HCSB in Hispanics/Latinos living in the US is an independent predictor of adult cigarette smoking, and this association appears to be strongest in Cubans and Puerto Ricans.

Addressing healthcare needs of people living below the poverty line: a rapid assessment of the Andhra Pradesh Health Insurance Scheme.

BACKGROUND: Families living below the poverty line in countries which do not have universal healthcare coverage are drawn into indebtedness and bankruptcy. The state of Andhra Pradesh in India established the Rajiv Aarogyasri Community Health Insurance Scheme (RACHIS) in 2007 with the aim of breaking this cycle by improving the access of below the poverty line (BPL) families to secondary and tertiary healthcare. It covered a wide range of surgical and medical treatments for serious illnesses requiring specialist healthcare resources not always available at district-level government hospitals. The impact of this scheme was evaluated by a rapid assessment, commissioned by the government of Andhra Pradesh. The aim of the assessment was to explore the contribution of the scheme to the reduction of catastrophic health expenditure among the poor and to recommend ways by which delivery of the scheme could be improved. We report the findings of this assessment. METHODS: Two types of data were used for the assessment. Patient data pertaining to 89 699 treatment requests approved by the scheme during its first 18 months were examined. Second, surveys of scheme beneficiaries and providers were undertaken in 6 randomly selected districts of Andhra Pradesh. RESULTS: This novel scheme was beginning to reach the BPL households in the state and providing access to free secondary and tertiary healthcare to seriously ill poor people. CONCLUSION: An integrated model encompassing primary, secondary and tertiary care would be of greater benefit to families below the poverty line and more cost-effective for the government. There is considerable potential for the government to build on this successful start and to strengthen equity of access and the quality of care provided by the scheme.

Secular trend in age at menarche in indigenous and nonindigenous women in Chile.

OBJECTIVES: To estimate the secular trend in age at menarche, comparing indigenous and nonindigenous women, and its relationship with socio-demographic, family and nutritional factors. METHODS: A study (historical cohorts) of 688 indigenous and nonindigenous women, divided into four birth cohorts (1960-69, 1970-79, 1980-89, and 1990-96) in an area in central southern Chile was carried out. Data and measurements were collected by health professionals using a previously validated questionnaire. Age at menarche was self-reported (recall). Adjusted differences among cohorts were estimated using a multivariate regression model. RESULTS: A secular trend (P < 0.001) in age at menarche was found in both ethnic groups, with no significant differences between them (P > 0.05). In an adjusted model, a reduction in age at menarche was estimated at 3.7 months per decade between 1960 and 1990. This trend was moderated by higher socio-economic level, smaller number of siblings, and cohabitation with a single parent during infancy. CONCLUSIONS: The trend has occurred in a steady progression over time in indigenous women, whereas in nonindigenous women, it was slow initially but has accelerated in recent years. Nonindigenous women have maintained a slightly lower age of menarche than their indigenous counterparts.

Trends in injury-related deaths before and after dissolution of the Union of Soviet Socialist Republics.

The relationship of death rates due to injury with the dissolution of the Soviet empire deserves special focus because of the impact of injury deaths on the productive working population between the ages of 15 and 65 years. A retrospective review was performed of annual mortality rates due to intentional and unintentional injuries, using WHO data from 1980 to 2003. Using data from a comparison group in Western Europe, the nations of the former Union of Soviet Socialist Republics (USSR) were studied. Annual death rates were examined using polynomial regression after 3-year moving averages smoothed the plots. The majority of trends in injury-related death noted in the comparison group decreased constantly over time. In contrast, many nations of the former USSR experienced an initial decrease, reaching a nadir in 1985 - 1987, followed by an increase in injury-related deaths. Moreover, many of these nations experienced a subsequent decrease following the dissolution of the USSR in 1991. The monitoring of trends in injury mortality in countries experiencing social and political upheavals is warranted.

Development and validation of the Patient-Physician Relationship Scale among patients with irritable bowel syndrome.

BACKGROUND: An effective patient-physician relationship (PPR) is essential to the care of patients with irritable bowel syndrome (IBS). We sought to develop and validate an IBS-specific instrument to measure expectations of the PPR. METHODS: We conducted structured focus groups about PPRs with 12 patients with IBS. Qualitative analysis was used to generate a questionnaire (the Patient-Physician Relationship Scale [PPRS]), which was modified with input from content experts and usability testing. For validation, we administered it online to US adults with IBS. Participants also completed the Functional Bowel Disorder Severity Index, the Rome III Adult Functional gastrointestinal (GI) Disorder Criteria Questionnaire, and modified versions of the Communication Assessment Tool (CAT-15) and Patient-Doctor Relationship Questionnaire (PDRQ-9). We performed principal components factor analysis for the PPRS. KEY RESULTS: The PPRS contained 32 questions with responses on a 7-item Likert scale. Themes included interpersonal features, clinical care expectations, and aspects of communication. One thousand and fifty-four eligible individuals completed the survey (88% completion rate). Most participants were middle aged (mean 48 years, SD 16.3), white (90%), and female (86%). Factor analysis showed only one relevant factor, relating to quality of PPR. The final scale ranged from possible-96 to +96 (mean 62.0, SD 37.6). It correlated moderately with the CAT-15 (r=.40, P<.001) and PDRQ-9 (r=.30, P<.001), establishing concurrent validity. CONCLUSIONS & INFERENCES: We describe the development and validation of the first questionnaire for use in measuring patient expectations of the PPR, which can be used for future outcomes studies and training physicians.

Natural history and patterns of current practice in heart failure. The Studies of Left Ventricular Dysfunction (SOLVD) Investigators.

A total of 6,273 consecutive relatively unselected patients with heart failure or left ventricular dysfunction, or both (mean age 62 +/- 12 years, mean ejection fraction 31 +/- 9%), were enrolled in the Studies of Left Ventricular Dysfunction (SOLVD) Registry over a period of 14 months. All patients were followed up for vital status and hospital admissions at 1 year. Ischemic heart disease was the underlying cause of failure or dysfunction in approximately 70% of patients, whereas hypertensive heart disease was considered to be primarily involved in only 7%. There were striking differences in the etiology of heart failure among blacks and whites: 73% of whites had an ischemic etiology of failure versus only 36% of blacks; 32% of blacks had a hypertensive condition versus only 4% of whites. The total 1-year mortality rate was 18%; 19% of patients had hospital admissions for heart failure and 27% either died or had a hospital admission for congestive heart failure during the 1st year of follow-up. Factors related to 1-year mortality or hospital admission for congestive heart failure included age, ejection fraction, diabetes mellitus, atrial fibrillation and female gender. There was no difference in mortality associated with congestive heart failure among blacks and whites, but hospital admissions for heart failure were more frequent in blacks. Digitalis and diuretic agents were the drugs most often used in these patients, who were often taking many medications in relation to severity of congestive heart failure symptoms and ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility and variability of the rectal mucosal proliferation index using proliferating cell nuclear antigen immunohistochemistry.

Rectal mucosal proliferation has been shown to be increased in patients with neoplastic lesions of the large bowel and may serve as a marker of risk for colorectal malignancy. We conducted analyses to determine reliability and components of variability that might suggest optimal analysis strategies for studies of proliferation. Endoscopic pinch biopsies were obtained from 17 adult patients, labeled using proliferating cell nuclear antigen, scored using strict rules, and then rescored. Labeling index, defined as the proportion of labeled cells in a crypt, was calculated for each crypt, biopsy, subject, and group. There was excellent reproducibility. The technician was able to select previously scored crypts 95% of the time. The overall labeling index was identical on repeat. There was considerable variability in labeling index among crypts from a single biopsy and between biopsies of a single subject. Variance component estimates suggested that 20% of the variability of labeling index was due to subject, 30% due to the biopsy within a subject, and 50% due to crypts within a biopsy. There were substantial gains in statistical power by scoring two biopsies rather than one. There was less gain from further increases in biopsy number. There was little statistical advantage for counting more than 8 crypts/biopsy. Demonstrating a decrease of 25% in the mean labeling index with 90% power could require more than 100 subjects/group. We conclude that proliferating cell nuclear antigen is an extremely reproducible method to determine proliferation index. There is considerable variability among subjects, biopsies, and crypts.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of rectal mucosal proliferation measured by proliferating cell nuclear antigen (PCNA) immunohistochemistry and whole crypt dissection.

Rectal mucosal proliferation has been promoted as an intermediate marker for risk of colorectal neoplasia. Proliferating cell nuclear antigen (PCNA) immunohistochemistry has become a standard method to measure cell proliferation. Whole-crypt dissection may provide a technically simpler method for determining proliferation within an entire crypt. We conducted a study to assess the reliability (reproducibility) of whole-crypt dissection in 10 subjects. Reliability of whole-crypt dissection with the subject as the unit of observation was excellent. The intraclass correlation coefficient for subjects was 0.93. Biopsy-to-biopsy reliability was lower (r=0.86) and crypt-to-crypt reliability lower still (r = 0.35). There was poor correlation between measures of proliferation index using the two techniques (Kendall's tau = 0.13; P = 0.08). Compartment analysis based on the percentage of the total number of labeled cells appearing in each crypt quartile also did not demonstrate a significant correlation between the two measures. We conclude that PCNA labeling index and whole-crypt mitotic count are not comparable measures of rectal mucosal proliferation.

School-based interventions improve heart health in children with multiple cardiovascular disease risk factors.

OBJECTIVE: To determine the immediate effects of two types of elementary school-based interventions on children with multiple cardiovascular disease (CVD) risk factors. DESIGN: Randomized, controlled field trial. SETTING: Conducted in 18 randomly selected elementary schools across North Carolina. STUDY PARTICIPANTS: Four hundred twenty-two children age 9 +/- 0.8 years with at least two risk factors at baseline: low aerobic power and either high serum cholesterol or obesity. INTERVENTION: Both 8-week interventions consisted of a knowledge and attitude program and an adaptation of physical education. The classroom-based intervention was given by regular teachers to all children in the 3rd and 4th grades. The risk-based intervention was given in small groups only to children with identified risk factors. Children in the control group received usual teaching and physical education. OUTCOME MEASURES: The primary outcome measure was cholesterol; additional measures were blood pressure, body mass index, body fat, eating and activity habits, and health knowledge. RESULTS: Both interventions produced large reductions in cholesterol (-10.1 mg/dL and -11.7 mg/dL) compared with a small drop (-2.3 mg/dL) in the controls. There was a trend for systolic blood pressure to increase less in both intervention groups than in the controls. Both intervention groups had a small reduction in body fat and higher health knowledge than the control group. CONCLUSIONS: Both brief interventions can improve the CVD risk profile of children with multiple risk factors. The classroom-based approach was easier to implement and used fewer resources. This population approach should be considered as one means of early primary prevention of CVD.

Children who prosper in unfavorable environments: the relationship to social capital.

OBJECTIVE: Social capital describes the benefits that are derived from personal social relationships (within families and communities) and social affiliations. This investigation examined the extent to which social capital is associated with positive developmental and behavioral outcomes in high-risk preschool children. DESIGN: A cross-sectional case-control analysis of young children "doing well" and "not doing well" at baseline in four coordinated longitudinal studies. PARTICIPANTS: A total of 667 2- to 5-year-old children (mean age, 4.4 years) and their maternal caregivers who are participating in the Longitudinal Studies of Child Abuse and Neglect Consortium. At recruitment, all children were characterized by unfavorable social or economic circumstances that contributed to the identification of the children as high risk. MEASURES: Social capital was defined as benefits that accrue from social relationships within communities and families. A social capital index was created by assigning one point to each of the following indicators: 1) two parents or parent-figures in the home; 2) social support of the maternal caregiver; 3) no more than two children in the family; 4) neighborhood support; and 5) regular church attendance. Outcomes were measured with the Child Behavior Checklist, a widely used measure of behavioral/emotional problems, and with the Battelle Developmental Inventory Screening Test, a standardized test that identifies developmental deficits. Children were classified as doing well if their scores on these instruments indicated neither behavioral nor developmental problems. RESULTS: Only 13% of the children were classified as doing well. The individual indicators that best discriminated between levels of child functioning were the most direct measures of social capital-church affiliation, perception of personal social support, and support within the neighborhood. The social capital index was strongly associated with child well-being, more so than any single indicator. The presence of any social capital indicator increased the odds of doing well by 29%; adding any two increased the odds of doing well by 66%. CONCLUSIONS: Our findings suggest that social capital may have an impact on children's well-being as early as the preschool years. In these years it seems to be the parents' social capital that confers benefits on their offspring, just as children benefit from their parents' financial and human capital. Social capital may be most crucial for families who have fewer financial and educational resources. Our findings suggest that those interested in the healthy development of children, particularly children most at risk for poor developmental outcomes, must search for new and creative ways of supporting interpersonal relationships and strengthening the communities in which families carry out the daily activities of their lives.

Studies of Left Ventricular Dysfunction (SOLVD) Registry: rationale, design, methods and description of baseline characteristics.

The Studies of Left Ventricular Dysfunction (SOLVD) comprises 2 double-blind, randomized clinical trials to test improved survival by angiotensin-converting enzyme inhibitor in patients with left ventricular dysfunction, with or without congestive heart failure. Patients entering the trials may be a highly selected subset of the population of such patients; those with the worst and best prognosis are likely to be excluded. To obtain the clinical history of a broader group, a registry of 6,273 patients included a relatively unselected cohort of patients with heart failure or left ventricular dysfunction, or both, from SOLVD hospitals. Registry data were obtained from hospital records. Because data collection from medical records may lead to incomplete data and more investigations in "sicker" patients, 898 randomly chosen subjects from different disease strata were seen in clinic where neurohumoral measures, echocardiograms, x-rays and electrocardiograms were obtained, and a 6-minute walking test was performed. The design and methodologic features, and the baseline characteristics of the participants in this 2-tiered registry are described, and its use in complementing the results and interpretation of the SOLVD trials is discussed.

The incidence of injuries in young people: II. Log-linear multivariable models for risk factors in a collaborative study in Brazil, Chile, Cuba and Venezuela.

Injuries and accidents are acknowledged as leading causes of morbidity and mortality among children and adolescents in the developing countries of the world. The Pan American Health Organization sponsored a collaborative study in four selected countries in Latin America to study the extent of the problem as well as to examine the potential risk factors associated with selected non-fatal injuries in the countries. The study subjects were injured children and adolescents (0-19 years of age) presenting at the study hospitals in chosen urban centres, as well as injured that were surveyed in households in the catchment areas of the hospitals. Study methods and descriptive frequency results were presented earlier. In this paper, log-linear multivariate regression models are used to examine the potentiating effects within country of several measured variables on specific types of injuries. The significance of risk factors varied between countries; however, some general patterns emerged. Falls were more likely in younger children, and occurred at home. The main risk factor for home accidents was the age of the child. The education of the head of the household was an important risk factor for the type of injury suffered. The likelihood of traffic accident injury varied with time of day and day of the week, but also was more likely in higher educated households. The results found are consistent with those found in other studies in the developed world and suggest specific areas of concern for health planners to address.

The incidence of injuries in young people: I. Methodology and results of a collaborative study in Brazil, Chile, Cuba and Venezuela.

Injuries and accidents are acknowledged as leading causes of mortality among children and adolescents in the developing countries of the world. However, little is known of the extent of non-fatal injuries and of their potential risk factors. The Pan American Health Organization sponsored the first collaborative study to examine morbidity incidence in specified areas of four selected countries in Latin America, and to test the feasibility and practicality of the developed methodology for application in other regions of the world. The study subjects were injured children and adolescents (0-19 years of age) presenting at the study hospitals in the chosen urban centres, as well as injured that were surveyed in households in the catchment area of the hospitals. Falls constituted the most common (40-52%) cause of injury in all areas, and tended to occur in the younger age groups. Motor vehicle injuries were not as frequent (5-24%) as expected from mortality studies. Males outnumbered females 2:1. The home was the most frequent (37-57%) site of injuries, especially for younger ages. Few received medical care at the site of the injury or en route to a hospital, if they went at all. The results found are consistent with those found in other studies in the developed world. The study methodology provides initial valid information for investigating the injury situation in countries with limited resources.

The Madurai Intraocular Lens Study. II: Clinical outcomes.

PURPOSE: To evaluate the safety and efficacy of extracapsular cataract extraction with posterior chamber intraocular lens (ECCE/PC-IOL) compared with intracapsular cataract extraction with aphakic glasses (ICCE-AG). METHODS: In a nonmasked randomized controlled clinical trial, 3,400 bilaterally vision-impaired patients aged 40 to 75 years with operable cataract were randomly assigned to receive either ICCE-AG or ECCE/PC-IOL at the Aravind Eye Hospital in India. The surgery was performed by one of four study surgeons. Patients were hospitalized for 5 postoperative days, with follow-up visits at 2, 6, and 12 months after discharge. Postsurgery evaluations were conducted by two independent study ophthalmologists. RESULTS: At any single postoperative follow-up time point, there were no statistically significant differences of clinical relevance between treatment groups for any complication of a serious nature except cystoid macular edema, which was more common with ICCE (4.2% vs 1.6%). In general, whether of a trivial, intermediate, or serious nature, complication rates were low at each evaluation time point. Cumulatively, the incidence of serious complications of all types throughout the 1-year study period was 14.5% for patients in the ICCE-AG group and 7.7% in the ECCE group (P < .001). Best-corrected visual acuity of 20/40 or better at 12 months was attained by 90.7% of ICCE-AG patients and 96.3% of ECCE/PC-IOL patients (P < .001). CONCLUSION: Although both operative procedures are safe and effective for cataract patients with bilateral impairment, ECCE/PC-IOL is superior to ICCE-AG in terms of both visual acuity restoration and safety.

Smoking initiation in youth: the roles of gender, race, socioeconomics, and developmental status.

PURPOSE: To describe smoking initiation, and to investigate factors that predict the early initiation of smoking in schoolchildren using a longitudinal approach. METHODS: A prospective study of smoking habits of children from the third and fourth grades through the eighth and ninth grades. The initial study population was 1970; 79.8% were white and 20.2% were African-American. Children were classified as "nonsmokers," "experimental smokers," or "current smokers" at five time points over 6 years. Multivariate regression models examined relationships of demographic and developmental factors with smoking initiation. RESULTS: Experimental smoking increased from 4% at Grades 3-4 to 42% at Grades 8-9, and current smoking prevalence rose from 0.4% to 9% over the same period. The mean age of initiation of smoking was 12.3 years. Smoking initiation (experimental smoking) was significantly different by racial group, socioeconomic status (SES), and pubertal development. White children and those of low SES were more likely to be experimental smokers, and also started earlier than African-American children and children of high SES. Once they started, white children advanced more rapidly to become current smokers. Boys had a higher prevalence of experimental smoking than girls at all time points. Children in rural areas were more likely than urban children to start smoking after age 12 years. Children who were at a higher pubertal stage than their peers were also more likely to experiment with smoking. CONCLUSIONS: Race, SES, and pubertal stage are important predictors of initiation of smoking in schoolchildren. This study indicates a need for smoking prevention classes in elementary and middle school, especially in areas with large numbers of white and low-SES youth. Also, smoking cessation programs, as well as smoking prevention classes, would be useful for middle school and high school students.

Statistical considerations for the interpretation of commonly utilized road traffic accident indicators: implications for developing countries.

The problem of increasing road traffic accidents and their consequences of death, injury and disability poses a growing concern, especially in developing countries. The objectives and nature of various indicators that countries with scarce economic resources can obtain are examined. The statistical and epidemiological considerations discussed should enable health care planners in developing countries to decide on the appropriate indicators required to properly assess the extent of the problem and aid in the amelioration and prevention of this "disease." Various indicators are discussed and a pragmatic guide examining their advantages and disadvantages is provided.

Repeated measures analysis of binary outcomes: applications to injury research.

Repeated measures are reasonably common in injury research and thus tools are required for appropriate analysis in order to account for the correlated nature of this type of data. Three methods for analyzing repeated measures binary outcome data are presented and contrasted: generalized estimating equations (GEE), a survey sample methodology, and logistic regression. These methods are applied to data collected from a cohort study of rugby players, designed to examine the risk and protective factors for rugby injury. It is not, however, the purpose of this paper to present causal models of rugby injuries. The GEE approach is attractive because it is able to account for the correlation among a subject's outcomes and several covariates can be included in a model. The survey sample method approach, which also accounts for the correlation but is restrictive in terms of the number of covariates it can handle, is another approach which is described. These two methods are contrasted to logistic regression, which assumes independence among a subject's outcomes. Under certain circumstances, the three methods do not differ substantially from one another. Under other circumstances, since logistic regression ignores the correlated nature of the data, standard errors may be incorrectly estimated and thus certain covariates may be incorrectly identified as significant predictors in a model.

Cardiovascular disease risk factors and obesity of rural and urban elementary school children.

Previous studies on the influence of a rural/urban setting on the prevalence of cardiovascular disease risk factors in children have not sufficiently controlled for socioeconomic status, race, gender, and perhaps, may not have included a representative sample of rural and urban children. This study compared the cardiovascular disease risk factors and rate of obesity of children living in rural and urban settings. It also determined the magnitude of the effect of the rural/urban setting on cardiovascular disease risk factors and obesity when controlling for race, socioeconomic status, and gender. The subjects were 2,113 third- and fourth-grade children; 962 from an urban setting and 1,151 from a rural setting. Height, weight, skinfolds, resting blood pressure, and total cholesterol levels were measured. Aerobic power (pVO2max) was estimated from cycle ergometry. Physical activity and smoking history were obtained from a questionnaire. Clustering analyses using adjustment for sample error indicated that total cholesterol, blood pressure, smoking, and physical activity levels of rural and urban children were not different (P > 0.10); however, body mass index and sum of skinfolds was greater for rural youth (P < 0.004). Logistic regression indicated that rural children had a 54.7 percent increased risk of obesity (P = 0.0001). This study's results indicate that, in children, a rural setting is associated with obesity, but not with the major risk factors associated with cardiovascular disease.

Ozone exposure and daily mortality in Mexico City: a time-series analysis.

Daily death counts in Mexico City were examined in relation to ambient ozone levels during 1990-1992 for the purpose of investigating the acute, irreversible effects of air pollution, with emphasis on ozone exposure. Air pollution data were obtained from nine monitoring stations operated by the Departamento del Distrito Federal. Mortality data were provided by the Instituto Nacional de Estadística, Geografía, e Informática. Increases in numbers of deaths were positively associated with elevated air pollution levels on the same day and on the previous day. The magnitude of the increases was small but statistically significant, after Poisson regression models were used to adjust for temperature and long-term trends. In models using data for a single pollutant, the "crude" ratio for total mortality associated with an increase of 100 parts per billion (ppb)* in one-hour maximum ozone concentration was 1.029 (95% CI 1.015, 1.044). A moving average of ozone showed a stronger association (rate ratio [RR] = 1.048, 95% CI 1.025, 1.070), and excess mortality (an increase in the number of deaths, relative to the average on days with low pollution levels) was more evident for persons over 65 years of age. Separate analyses of the effect of elevated ozone for different areas of the city showed similar results, but they were not statistically significant. Other pollutants also were related to mortality. The RR was 1.075 (95% CI 0.984, 1.062) per 100-ppb increase for sulfur dioxide and 1.049 (95% CI 1.030, 1.067) per 100 micrograms/m3 increase in total suspended particulates (TSP) when these pollutants were considered in separate models. However, when all three pollutants were considered simultaneously, only TSP remained associated with mortality, indicating excess mortality of 5% per 100 micrograms/m3 increase [RR = 1.052, 95% CI 1.034, 1.072]. The excess mortality associated with TSP is consistent with that observed in other cities in America and Europe. This study provides some evidence that ozone is associated with all-cause mortality and with mortality among the elderly after controlling for long-term cycles. However, ozone levels exhibited little or no effect on mortality rates when other air pollutants were considered simultaneously. Particulate matter appeared to be an important pollutant; it independently predicted changes in mortality. Nevertheless, because of the complexity and variability of the mixtures to which people are exposed, it is difficult to attribute the observed effects to a single pollutant. The technical feasibility and scientific validity of isolating the effect of single pollutants in such complex mixtures requires further research and careful consideration. Given the large population living in and exposed to ambient air pollution in Mexico City and other metropolises throughout the world, these small but significant associations of mortality with air pollution indices are of public health concern.