In a prospective study of infants' exposure to nitrogen dioxide (NO2)* and respiratory illness, NO2 concentrations were measured in more than 1,400 homes in Albequerque, NM, From January 1988 through June 1991 (Health Effects Institute Research Report Number 58, Parts I, II and III). This report characterizes the variability in indoor NO2 concentrations across seasons and years, and identifies factors associated with variation in concentrations between homes and across seasons. In regression analyses of winter data, NO2 levels in the infants' bedrooms were predominately determined by the presence of gas cooking ranges with continuously burning pilot lights, the presence of wall or floor furnaces, the use of the stove for space heating, and the square footage of the living space. These findings are consistent with previously published analysis of data from homes in other U.S. cities. Relatively small differences in seasonal NO2 levels were observed across years. The correlation coefficient (r) of bedroom NO2 levels obtained in the same homes was 0.66 over two winters and 0.48 over two summers. For homes that had gas cooking ranges with continuously burning pilot lights, the NO2 bedroom concentrations differed, on average, less than 5 parts per billion (ppb) across winters. These differences were hypothesized to be caused by differences in the use of indoor NO2 sources, ventilation, and ambient (outdoor) NO2 levels. We were, however, unable to demonstrate an association between year-to-year differences in seasonal indoor NO2 concentrations and reported use of cooking range, furnace, or heater, or ambient NO2 levels, or temperature.

This report describes the quality assurance and quality control program developed for the previously reported epidemiologic study of nitrogen dioxide (NO2) and respiratory illness in children (Health Effects Institute Research Report 58, Parts I and II). The specific aims of the program were to make certain that data were sufficiently accurate, complete, verifiable, and retrievable. The quality assurance and quality control program consisted of: a written protocol, standard operating procedures, written records, a project management system, appropriate data processing, data verification, and data analysis planning, and was staffed by qualified and appropriately trained personnel. Within the activities of the overall program, two focused quality assurance studies were conducted. During the first of these focused studies, parents maintained a calendar-diary of their child's daily respiratory symptoms. Telephone interviews were conducted at intervals of two weeks, and parents used the calendars to report on symptom occurrence since the previous call. To assess the comparability of illness events based on symptom reports from the parents with usual clinical diagnostic methods, nurse practitioners examined children during illness, and office and clinic records of outpatient visits were reviewed. Using the parent reports, respiratory illnesses were defined as symptom episodes of at least two consecutive days; lower respiratory illnesses included at least one day of either wet cough or wheeze. Runny or stuffy nose was reported for 93% of illnesses; and wet cough for 33% and wheeze for 6% of illnesses. In comparison with the diagnoses made by a nurse practitioner, parent reports of wet cough or wheeze were sensitive (93.4%) for detecting lower respiratory illnesses, but nonspecific (with specificity of only 24.2%). The majority of the false-positive lower respiratory illnesses had the symptom of wet cough. The comparison of parent reports with outpatient records provided similar findings. These findings indicate that standardized reporting of respiratory illnesses can be achieved with regular telephone interviews, but the classification of specific illnesses from the observations of parents' information may differ from diagnoses made by clinicians. The second focused quality assurance study evaluated the measurement error associated with the parents' use of passive diffusion samplers for NO2. Midway through the study, technicians conducted home visits to assess compliance with stated procedures, and to make independent measurements of NO2. Based on criteria for placement and use of the samplers, conditions of noncompliance were observed on about 40% of visits.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated measurements of nitrogen dioxide were obtained from 1988 to 1991 in the homes of 1,205 infants living in Albuquerque, NM. Passive diffusion samplers were used to obtain a series of two-week integrated measurements from the home of each infant for use in a cohort study of the relation of residential exposure to nitrogen dioxide and respiratory illnesses. Information on stove use and time spent inside the residence was collected at two-week and two-month intervals, respectively. During the winter, in the bedrooms of homes with gas cooking stoves, mean nitrogen dioxide concentrations were 21 parts per billion (ppb); mean concentrations in the living room and kitchen were 29 ppb and 34 ppb, respectively. In homes with electric cooking stoves, the mean bedroom concentration was 7 ppb during the winter. Lower indoor concentrations were observed during the summer in homes with both gas and electric stoves. On average, infants spent approximately 12.3 hours per day in their bedrooms, 7.3 hours in the living rooms, 35 minutes in the kitchens, and 3.8 hours out of their homes. (As a condition of participation, none of the infants spent more than 20 hours per week in day care outside of their homes). The mean time infants spent in the kitchen during cooking was approximately nine minutes per day. We tested whether exposures of infants living in homes with gas stoves could be reasonably estimated by measurements in the bedroom in comparison with time-weighted average concentrations based on time-activity data and simultaneous nitrogen dioxide measurements in the kitchen, living room, and bedroom. In 1,937 two-week intervals from 587 infants, 90% of time-weighted exposure (on the three-level classification used in this study) estimates were in agreement with estimates based on bedroom concentrations alone. The agreement of the time-weighted nitrogen dioxide exposure estimates with the bedroom concentrations is attributed to limited amounts of cooking stove use (the mean was 29 minutes per day), small room-to-room differences in nitrogen dioxide concentrations (the mean kitchen-bedroom difference was 12 ppb), and the relatively large proportion of time that infants spent in their bedrooms.

We have carried out a prospective cohort study to test the hypothesis that exposure to nitrogen dioxide increases the incidence and severity of respiratory infections during the first 18 months of life. Between January 1988 and June 1990, 1,315 infants were enrolled into the study at birth and followed with prospective surveillance for the occurrence of respiratory infections and monitoring of nitrogen dioxide concentrations in their homes. The subjects were healthy infants from homes without smokers; they were selected with stratification by type of cooking stove at a ratio of four to one for gas and electric stoves. Illness experience was monitored by a daily diary of symptoms completed by the mother and a telephone interview conducted every two weeks. Illnesses with wheezing or wet cough were classified as involving the lower respiratory tract; all other respiratory illnesses were designated as involving the upper respiratory tract. Exposure to nitrogen dioxide was estimated by two-week average concentrations measured in the subjects' bedrooms with passive samplers. This analysis is limited to the 1,205 subjects completing at least one month of observation; of these, 823 completed the full protocol, contributing 82.8% of the total number of days during which the subjects were under observation. Incidence rates for all respiratory illnesses, all upper respiratory illness, all lower respiratory illnesses, and lower respiratory illness further divided into those with any wheezing, or wet cough without wheezing, were examined within strata of nitrogen dioxide exposure at the time of the illness, nitrogen dioxide exposure during the prior month, and type of cooking stove. Consistent trends of increasing illness incidence rates with increasing exposure to nitrogen dioxide were not evident for either the lagged or unlagged exposure variables. The effect of nitrogen dioxide exposure on illness occurrence during at-risk intervals of two weeks' duration was examined using the generalized estimating equation approach. In these multivariate analyses, none of the odds ratios was significantly elevated for unlagged nitrogen dioxide exposures, lagged nitrogen dioxide exposures, or stove type. Duration of illness was assessed in relation to the same exposure variables; illness duration and nitrogen dioxide exposure were not associated. We have found that indoor exposure to nitrogen dioxide is associated with neither the incidence nor the duration of respiratory illnesses. The study was designed to have sufficient power to detect effects of nitrogen dioxide exposure of magnitudes previously reported and in a range relevant to public health concern; the lack of association cannot be attributed to potential bias from misclassification of outcome or exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicologic and epidemiologic studies have elevated concern that exposure to nitrogen dioxide (NO2) in outdoor and indoor air may increase the frequency and severity of respiratory infections. We have developed and implemented a prospective cohort study to test the hypothesis that exposure to NO2 increases the incidence and severity of respiratory infections during the first 18 mo of life. This study, which was based on extensive pilot research, was designed to address the potential limitations of misclassification, confounding, and inadequate power. Enrollment of 1 315 subjects has been completed. This paper reviews the methods used in the study, characteristics of the enrolled subjects, NO2 concentrations in the homes of study participants, and rates of illness occurrence.