Do recent data from the Seychelles Islands alter the conclusions of the NRC Report on the toxicological effects of methylmercury?

In 2000, the National Research Council (NRC), an arm of the National Academy of Sciences, released a report entitled, "Toxicological Effects of Methylmercury." The overall conclusion of that report was that, at levels of exposure in some fish- and marine mammal-consuming communities (including those in the Faroe Islands and New Zealand), subtle but significant adverse effects on neuropsychological development were occurring as a result of in utero exposure. Since the release of that report, there has been continuing discussion of the public health relevance of current levels of exposure to Methylmercury. Much of this discussion has been linked to the release of the most recent longitudinal update of the Seychelles Island study. It has recently been posited that these findings supercede those of the NRC committee, and that based on the Seychelles findings, there is little or no risk of adverse neurodevelopmental effects at current levels of exposure. In this commentary, members of the NRC committee address the conclusions from the NRC report in light of the recent Seychelles data. We conclude that no evidence has emerged since the publication of the NRC report that alters the findings of that report.

Ambient, indoor and personal exposure relationships of volatile organic compounds in Mexico City Metropolitan Area

Air pollution standards and control strategies are based on ambient measurements. For many outdoor air pollutants, individuals are closer to their sources (especially traffic) and there are important indoor sources influencing the relationship between ambient and personal exposures. This paper examines the relationship between volatile organic compounds (VOCs) measured at central site monitoring stations and personal exposures in the Mexico City Metropolitan Area. Over a 1-year period, personal exposures to 34 VOCs were measured for 90 volunteers from 30 families living close to one of five central monitoring stations. Simultaneous 24-h indoor, outdoor and central site measurements were also taken. Dual packed thermal desorption tubes and C(18) DNPH-coated cartridges were used for sampling VOCs and these were analyzed by GC/MS and HPLC, respectively. A factor analysis of the personal exposure data aided in grouping compounds by the most likely source type: vehicular (BTEX, styrene and 1,3-butadiene), secondary formed or photochemical (most aldehydes), building materials and consumer products (formaldehyde and benzaldehyde), cleaning solvents (tetrachloroethene and 1,1,1-trichloroethane), volatilization from water (chloroform and trichloroethene) and deodorizers (1,4-dichlorobenzene). Mean ambient, indoor and personal concentrations were 7/7/14 microg/m(3) for benzene, 1/3/3 for 1,3-butadiene, 6/20/20 for formaldehyde and 3/9/50 for 1,4-dichlorobenzene. Geometric mean (GM) ambient concentrations of trichloroethene and carbon tetrachloride were similar to GM personal exposures. While outdoor and indoor home GM concentrations for most vehicular related compounds (benzene, MTBE, xylenes and styrene) were comparable, the GM personal exposures were twice as high. Indoor concentrations of 1,3-butadiene, 1,1,1-trichloroethane, tetrachloroethane, chloroform, formaldehyde, valeraldehyde, propionaldehyde and n-butyraldehyde were comparable to personal exposures. For certain compounds, such as chloroform, aldehydes, toluene, 1,3-butadiene and 1,4-dichlorobenzene, GM personal exposures were more than two times greater than GM ambient measurements.

The relationship between human semen parameters and environmental exposure to polychlorinated biphenyls and p,p'-DDE

Scientific and public concern exists about potential reproductive health effects of persistent chlorinated organic chemicals, such as polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), and dichlorodiphenyldichloroethylene (DDE, the most stable daughter compound of DDT). To explore the hypothesis that environmental exposures to PCBs and DDE are associated with altered semen parameters, we conducted a cross-sectional study of 212 male partners of subfertile couples who presented to the Massachusetts General Hospital Andrology Laboratory. Semen parameters were analyzed as both a continuous measure and dichotomized based on World Health Organization reference values for sperm concentration (< 20 million/mL), motility (< 50% motile), and Kruger strict criteria for morphology (< 4% normal). The comparison group for the dichotomized analysis was men with all three semen parameters above the reference values. In serum, 57 PCB congeners and p,p -DDE were measured by congener-specific analysis using gas chromatography with electron capture detection. There were dose-response relationships among PCB-138 and sperm motility (odds ratio per tertile, adjusted for age, abstinence, and smoking, and p-value for trend were, respectively, 1.00, 1.68, 2.35, and p-value = 0.03) and morphology (1.00, 1.36, 2.53, p-value = 0.04). There was limited evidence of an inverse relationship between sum of PCBs, as well as those PCBs classified as cytochrome P450 enzyme inducers, with sperm motility and sperm morphology, as well as limited evidence of an inverse association between p,p -DDE and sperm motility. The lack of a consistent relationship among semen parameters and other individual PCB congeners and groupings of congeners may indicate a difference in spermatotoxicity between congeners.

Cortical mechanisms for acquisition and performance of bimanual motor sequences

We used functional magnetic resonance imaging to investigate the cortical mechanisms contributing to the acquisition and performance of a complex, bimanual motor sequence. To that aim, five subjects were trained on a difficult, asymmetrical finger opposition task. Their performance rate almost doubled in the course of training and approached the performance rate in an untrained, symmetrical finger opposition task. Before training, performance of the asymmetrical sequence was associated with activity in M1, premotor cortex, supplementary motor cortex, and parietal cortex. After training, performance of the asymmetrical sequence was associated mainly with activity in M1, and little activity outside M1 remained. The latter pattern of cortical activation resembled that observed during the execution of symmetrical sequences, which was unaffected by practice with the asymmetrical sequence. The activation pattern obtained with the symmetrical bimanual sequence was indistinguishable from the combined activation measured in contralateral hemispheres during unimanual control sequences. The data indicate that cortical regions previously implicated in the acquisition of difficult unimanual motor sequences also contribute to the acquisition of asymmetrical bimanual sequences. We found no evidence for an expansion of activity in M1 after acquisition of the asymmetrical sequence (while this has been reported after acquisition of unimanual sequences). In the context of existing literature, the data suggest that the acquisition of unimanual and bimanual motor sequences may rely on similar cortical mechanisms, but that the formation of long-term, procedural memories for the two types of sequences might at least in part depend on different mechanisms.

The relationship between environmental exposures to phthalates and DNA damage in human sperm using the neutral comet assay

Phthalates are industrial chemicals widely used in many commercial applications. The general population is exposed to phthalates through consumer products as well as through diet and medical treatments. To determine whether environmental levels of phthalates are associated with altered DNA integrity in human sperm, we selected a population without identified sources of exposure to phthalates. One hundred sixty-eight subjects recruited from the Massachusetts General Hospital Andrology Laboratory provided a semen and a urine sample. Eight phthalate metabolites were measured in urine by using high-performance liquid chromatography and tandem mass spectrometry; data were corrected for urine dilution by adjusting for specific gravity. The neutral single-cell microgel electrophoresis assay (comet assay) was used to measure DNA integrity in sperm. VisComet image analysis software was used to measure comet extent, a measure of total comet length (micrometers); percent DNA in tail (tail%), a measure of the proportion of total DNA present in the comet tail; and tail distributed moment (TDM), an integrated measure of length and intensity (micrometers). For an interquartile range increase in specific gravity-adjusted monoethyl phthalate (MEP) level, the comet extent increased significantly by 3.6 micro m [95% confidence interval (95% CI), 0.74-6.47]; the TDM also increased 1.2 micro m (95% CI, -0.05 to 2.38) but was of borderline significance. Monobutyl, monobenzyl, monomethyl, and mono-2-ethylhexyl phthalates were not significantly associated with comet assay parameters. In conclusion, this study represents the first human data to demonstrate that urinary MEP, at environmental levels, is associated with increased DNA damage in sperm.

Day care attendance in early life, maternal history of asthma, and asthma at the age of 6 years

Among children not selected on the basis of a parental history of atopy, day care attendance in early life is inversely associated with asthma at school age. We examined the relation between day care in the first year of life and asthma, recurrent wheezing, and eczema at the age of 6 years and wheezing in the first 6 years of life among 453 children with parental history of atopy followed from birth. Among all study participants, day care in the first year of life was inversely associated with eczema (odds ratio [OR] = 0.3, 95% confidence interval [CI] = 0.1-0.8). Day care attendance in early life was associated with a decreased risk of asthma (OR = 0.3, 95% CI = 0.1-0.7) and recurrent wheezing (OR = 0.3, 95% CI = 0.1-0.9) at the age of 6 years and with a decreased risk of any wheezing after the age of 4 years only among children without maternal history of asthma. Among children with maternal history of asthma, day care in early life had no protective effect on asthma or recurrent wheezing at the age of 6 years but was instead associated with an increased risk of wheezing in the first 6 years of life. Our findings suggest that maternal history of asthma influences the relation between day care-related exposures and childhood asthma.

Phthalate exposure and human semen parameters

BACKGROUND

There is scientific and public concern about commonly used chemicals, including phthalates, that are associated with reproductive toxicity in laboratory animals and are hormonally active. People are exposed to phthalates through diet, consumer products and medical devices. The present study explored whether environmental levels of phthalates are associated with altered semen quality in humans.

METHODS

We recruited 168 men who were part of subfertile couples and who presented to the Massachusetts General Hospital andrology laboratory for semen analysis between January 2000 and April 2001. Semen parameters were dichotomized based on 1999 World Health Organization reference values for sperm concentration (< 20 million/ml) and motility (< 50% motile), as well as Tygerberg Strict criteria for morphology (< 4% normal). The comparison group was men for whom these semen parameters were all above the reference values. In urine, eight phthalate metabolites were measured with high-performance liquid chromatography and tandem mass spectrometry. Specific gravity-adjusted phthalate metabolite levels were categorized into tertiles.

RESULTS

There was a dose-response relation between tertiles of mono-butyl phthalate and sperm motility (odds ratio per tertile = 1.0, 1.8, 3.0; P-value for trend = 0.02) and sperm concentration (1.0, 1.4, 3.3; P-value for trend = 0.07). In addition, there was a dose-response relation between tertiles of mono-benzyl phthalate and sperm concentration (1.0, 1.4, 5.5; P-value for trend = 0.02).

CONCLUSIONS

There were dose-response relations for monobutyl phthalate and monobenzyl phthalate with one or more semen parameters, and suggestive evidence for monomethyl phthalate with sperm morphology. The lack of a relation for other phthalates may indicate a difference in spermatotoxicity among phthalates.

Mixed models for assessing correlation in the presence of replication

The need to assess correlation in settings where multiple measurements are available on each of the variables of interest often arises in environmental science. However, this topic is not covered in introductory statistics texts. Although several ad hoc approaches can be used, they can easily lead to invalid conclusions and to a difficult choice of an appropriate measure of the correlation. Lam et al. approached this problem by using maximum likelihood estimation in cases where the replicate measurements are linked over time, but the method requires specialized software. We reanalyze the data of Lam et al. using PROC MIXED in SAS and show how to obtain the parameter estimates of interest with just a few lines of code. We then extend Lam et al.'s method to settings where the replicate measurements are not linked. Analysis of the unlinked case is illustrated with data from a study designed to assess correlations between indoor and outdoor measurements of benzene concentration in the air.

Bottle feeding in the bed or crib before sleep time and wheezing in early childhood

OBJECTIVE

Bottle feeding in the bed or crib before sleep time has been associated with an increased risk of wheezing in the first year of life. We examined whether bottle feeding in the bed or crib before sleep time in the first year of life is associated with wheezing in the first 5 years of life.

METHODS

In a prospective cohort study of 448 children with parental history of atopy followed from birth, we examined the relation between the number of bimonthly parental reports of bottle feeding in the bed or crib before sleep time in the first year of life (range: 0-6 reports) and parental report of wheezing in the first 5 years of life. Additional outcome measures included recurrent wheezing (> or =2 episodes of wheezing in the previous year) and asthma (physician-diagnosed asthma and > or =1 episode of wheezing in the previous year) at the age of 5 years.

RESULTS

The risk of recurrent wheezing and asthma at 5 years of age increased significantly with each additional report of bottle feeding in the bed or crib before sleep time in the first year of life. The risk of wheezing between the ages of 1 and 5 years increased with each additional report of bottle feeding in the bed or crib before sleep time in the first year of life. As an example, a child whose parents reported bottle feeding in the bed or crib before sleep time on 3 occasions in the first year of life had 1.5 times higher risk of wheezing between the ages of 1 and 5 years than a child whose parents did not report bottle feeding in the bed or crib before sleep time in the first year of life (95% confidence interval for relative risk: 1.12-2.12).

CONCLUSIONS

Among children with parental history of atopy, bottle feeding in the bed or crib before sleep time in the first year of life is a risk factor for recurrent wheezing and asthma at 5 years of age and a risk factor for wheezing between the ages of 1 and 5 years.

Fractalkine (CX3CL1) and brain inflammation: Implications for HIV-1-associated dementia

Leukocyte migration and activation play an important role in immune surveillance and the pathogenesis of a variety of neurodegenerative disorders, including human immunodeficiency virus (HIV)-1-associated dementia (HAD). A novel chemokine named fractalkine (FKN, CX3CL1), which exists in both membrane-anchored and soluble isoforms, has been proposed to participate in the generation and progression of inflammatory brain disorders. Upon binding to the CX3C receptor one (CX3CR1), FKN induces adhesion, chemoattraction, and activation of leukocytes, including brain macrophages and microglia (MP). Constitutively expressed in the central nervous system (CNS), mainly by neurons, FKN is up-regulated and released in response to proinflammatory stimuli. Importantly, FKN is up-regulated in the brain tissue and cerebrospinal fluid (CSF) of HAD patients. Together, these observations suggest that FKN and its receptor have a unique role in regulating the neuroinflammatory events underlying disease. This review will examine how FKN contributes to the recruitment and activation of CX3CR1-expressing MP, which are critical events in the neuropathogenesis of HAD.

A longitudinal analysis of wheezing in young children: the independent effects of early life exposure to house dust endotoxin, allergens, and pets

BACKGROUND

It has been postulated that exposure to bacterial endotoxins and animals early in life might confer protection against the development of asthma and allergies.

OBJECTIVE

We investigated the longitudinal effects of exposure to house dust endotoxin (HDE), allergen levels, and the presence of a dog in the home on wheezing in young children over a 4-year period.

METHODS

Two hundred twenty-six children younger than 5 years were followed for 4 years. Endotoxin and allergen levels were measured from house dust collected at baseline. Longitudinal associations were investigated by using a proportional hazards technique that allowed for multiple outcomes per subject.

RESULTS

Exposure to high concentrations of HDE of greater than the median level was associated with an increased risk for wheezing over the period of observation (multivariate relative risk, 1.52; 95 % CI, 1.07-2.14), but this risk rapidly decreased over time (P for trend =.005). Exposure to cockroach allergen was associated with increased risk for wheezing, whereas exposure to cat allergen and the presence of a dog in the home were both associated with decreased risk for wheezing. The risks associated with cockroach allergen, cat allergen, and dog did not change over the period of observation.

CONCLUSION

The negative associations between exposures to dogs and cat allergen and wheeze appear to be independent of the effects of endotoxin and suggest that separate mechanisms might mediate the effects of HDE exposure and pet exposure on the developing immune system.

Exposure to cat allergen, maternal history of asthma, and wheezing in first 5 years of life

We looked for an association between early exposure to pets and asthma and wheezing in children whose mothers or fathers did or did not have a history of asthma. We followed up 448 children, who had at least one parent with a history of atopy, from birth to 5 years. Among children whose mothers had no history of asthma, exposure to a cat or a Fel d 1 concentration of at least 8 microg/g at the age of 2-3 months was associated with a reduced risk of wheezing between the ages of 1 and 5 years. However, among children whose mothers did have a history of asthma, such exposures were associated with an increased risk of wheezing at or after the age of 3 years. There was no association between wheezing and exposure to dog or dog allergen, and the father's allergy status had no effect on the relation between childhood wheezing and cat exposure.

Caretaker-child concordance for child's exposure to violence in a preadolescent inner-city population

BACKGROUND

Effective screening for exposure to violence (ETV) in the pediatric setting depends on informant reliability and recognition of patients at increased risk. Pediatricians screening for children's ETV often rely on parent reporting.

HYPOTHESIS

That there would be poor caretaker-child concordance given that children would report events occurring outside the home not witnessed by the caretaker and that ETV would be higher among immigrant families.

OBJECTIVES

To examine concordance between caretaker and child self-report of the child's ETV in a preadolescent population and to explore factors related to increased risk.

DESIGN

Community-based survey.

SETTING

Urban community health center.

PARTICIPANTS

One hundred sixty-five caretaker-child pairs.

METHODS

The ETV was assessed by means of a standardized interview questionnaire on location and frequency of ETV. A Rasch model was used to develop summary scores of ETV (frequency and severity).

RESULTS

Caretaker-child concordance on reports of child's ETV was poor. The kappa statistics ranged from -0.04 for seeing someone knifed to 0.39 for witnessing a shooting. Children reported ETV more often in their neighborhood or at school, whereas caretakers reported more events near or at home. Univariate predictors of child's self-reported ETV were female sex (beta +/- SE, -10.1 +/- 4.6; P =.03) and caretaker being divorced (beta +/- SE, 12.6 +/- 6.0; P =.04). In multivariate analyses, country of origin predicted child's ETV, adjusting for child's age and sex, and caretaker educational status and marital status.

CONCLUSIONS

Caretakers and their children have poor agreement on reports of the child's ETV. Intervention strategies around ETV should include assessment of the child independent of caretaker report for preadolescents. Screening may be more effective if pediatricians are aware of factors related to increased risk, including immigration status and caretaker marital status.

Lack of association between antibiotic use in the first year of life and asthma, allergic rhinitis, or eczema at age 5 years

Five retrospective studies have reported an association between antibiotic use in early life and asthma in childhood. We studied the relationship between the use of oral antibiotics in the first year of life and asthma, allergic rhinitis, and eczema at age 5 years among 448 children with a parental history of atopy monitored from birth. After adjustment for potential confounders, we found no significant association between antibiotic use in the first year of life and asthma (odds ratio [OR] for one versus no courses of antibiotics, 0.5; 95% confidence interval [CI] for OR, 0.2 to 1.5; OR for two or more versus no courses of antibiotics, 1.0; 95% CI for OR, 0.5 to 2.2), recurrent wheezing, allergic rhinitis, or eczema at age 5 years. There was no significant association between antibiotic use in the first year of life and having at least one of three atopic diseases (asthma, allergic rhinitis, or eczema) at age 5 years (OR for one versus no courses of antibiotics, 0.7; 95% CI, 0.4 to 1.4; OR for two or more versus no courses of antibiotics, 0.9; 95% CI, 0.5 to 1.4). Our findings do not support the hypothesis that antibiotic use in early life is associated with the subsequent development of asthma and atopy in childhood.

Hippocampal complex and retrieval of recent and very remote autobiographical memories: evidence from functional magnetic resonance imaging in neurologically intact people

It has been argued that the role of the hippocampus in memory is time-limited: during a period of memory consolidation, other brain regions such as the neocortex are said to acquire the ability to support memory retention and retrieval on their own. An alternative view is that retention and retrieval of memory for autobiographical episodes depend on the hippocampal complex, regardless of the age of the memory. We examined the participation of the hippocampal complex in a functional magnetic resonance imaging (fMRI) study in which participants were asked to recollect autobiographical events that occurred either within the last 4 years or more than 20 years ago. We found equivalent levels of hippocampal activation in both conditions in all participants (N = 10). In addition, activation in neocortical regions did not differ as a function of the age of the memory, even though most of the recent memories recalled were less than 2 years old and the remote memories more than 35 years old. The results support the notion that the hippocampal complex participates in retention and recovery of even very old autobiographical memories, and place boundary conditions on theories of memory consolidation.

Modeling spatial survival data using semiparametric frailty models

We propose a new class of semiparametric frailty models for spatially correlated survival data. Specifically, we extend the ordinary frailty models by allowing random effects accommodating spatial correlations to enter into the baseline hazard function multiplicatively. We prove identifiability of the models and give sufficient regularity conditions. We propose drawing inference based on a marginal rank likelihood. No parametric forms of the baseline hazard need to be assumed in this semiparametric approach. Monte Carlo simulations and the Laplace approach are used to tackle the intractable integral in the likelihood function. Different spatial covariance structures are explored in simulations and the proposed methods are applied to the East Boston Asthma Study to detect prognostic factors leading to childhood asthma.

Parental exposure to organic solvents and reduced birth weight

The authors investigated the association of birth weight with maternal and paternal exposure to organic solvents in 1,222 couples employed in a large petrochemical corporation in Beijing, China, during the period between 1994 and 1998. A trained interviewer assessed parental exposures to organic solvents. The authors used generalized additive models to examine the association between birth weight and parental exposure to organic solvents. After the authors adjusted for potential confounders, maternal exposure to solvents was significantly associated with reduced birth weight (-81.7 gm, 95% confidence interval = -106.3, -3.1), and reduced birth weights of female babies and of younger mothers' babies were statistically significant. Maternal exposure to organic solvents was associated with reduced birth weight in this population, but paternal exposure to organic solvents was not similarly associated.

Reliability of the comet assay in cryopreserved human sperm

BACKGROUND

Although the comet assay has potential value for measuring DNA damage in large epidemiological human sperm studies, it is impractical to perform the assay daily on fresh semen samples. Therefore, before its use in epidemiological studies, the reliability of the comet assay in measuring DNA damage in cryopreserved sperm should be compared with that in fresh human sperm.

METHODS

Semen samples from 16 men were cryopreserved in liquid nitrogen (LN) using four methods: flash freezing with and without cryopreservative, and programmable freezing with and without cryopreservative. Neutral microgel electrophoresis was performed and comets were stained with YOYO-1. Comet length was measured using an eyepiece micrometer at x400 magnification.

RESULTS

The highest correlation was between comet assay results obtained from fresh human semen compared with semen flash frozen without cryopreservative (R = 0.88). However, the method of cryopreservation, as compared with other sources of variability, accounted for only 6% of the variability. Inter-individual variability accounted for 20%, and individual sperm-to-sperm variability within an ejaculate accounted for 65%.

CONCLUSIONS

Flash-freezing in LN without cryopreservative most closely reproduced the results obtained using fresh human semen samples, and thereby represents the most appropriate cryopreservation method for human semen in epidemiological studies utilizing the neutral comet assay.

Environmental organochlorines and semen quality: results of a pilot study

There have been numerous studies that suggest that sperm concentrations (sperm counts) are declining in men. However, other studies suggest that sperm counts are not declining or may be increasing in some areas. Although there is disagreement on whether there is a downward temporal trend in sperm counts, the studies provide evidence that sperm counts vary by geographic location. It has been hypothesized that the geographic variation in sperm concentrations may be due to environmental exposures, lifestyle factors, or some unknown causes. To determine whether contemporary ambient levels of polychlorinated biphenyls (PCBs) and p,p-DDE are associated with altered semen quantity and quality, we selected a study population without specific exposure to PCBs or p,p-DDE. The present study presents the results from a pilot study on the relationship between serum PCBs and p,p-DDE and semen quality in 29 subjects recruited from the Massachusetts General Hospital Andrology Laboratory. Of the 29 subjects, 3 had sperm concentrations < 20 million/mL, 7 had < 50% motile sperm, 9 had < 4% normal morphology, and 6 were below normal in more than one semen parameter. The 18 subjects with normal spermatozoa concentration, motility, and morphology were used as comparison subjects. The mean (SE) concentration of the sum of PCBs and p,p-DDE was 242 ng/g lipids (34.0) and 354 ng/g lipids (120), respectively, for men with below normal motility as compared to 202 ng/g lipids (16.6) and 240 ng/g lipids (31.1), respectively, for the comparison subjects. The data showed general trends that were suggestive of an association between PCBs and p,p-DDE and abnormal motility, as well as with sperm concentration and morphology. A full-scale study is currently in progress.

Day care attendance, respiratory tract illnesses, wheezing, asthma, and total serum IgE level in early childhood

BACKGROUND

It has been hypothesized that day care--related infections may explain the inverse relation between day care attendance in early life and asthma in childhood.

OBJECTIVE

To examine the relation between day care attendance or respiratory tract illnesses in the first year of life and wheezing and asthma in the first 4 years of life among children with a parental history of atopy who were followed up from birth.

RESULTS

Day care attendance in the first year of life was inversely associated with geometric mean total serum IgE level (12.9 [+/-1 SD = 3.3, 51.4] IU/mL for day care vs 18.5 [[+/-1 SD = 5.3, 64.7] IU/mL for no day care; P =.03) at 2 years of age but not significantly associated with wheezing at or after 2 years of age. Having at least 1 physician-diagnosed lower respiratory tract illness in the first year of life was significantly associated with recurrent wheezing (odds ratio [OR], 2.0; 95% confidence interval [CI], 1.0-4.1) and asthma (OR, 2.5; 95% CI, 1.1-5.5) at 4 years of age, but not with any wheezing (infrequent and frequent) at 3 years or older. Illnesses of the upper respiratory tract (> or = 1 physician-diagnosed upper respiratory tract illness or > or = 3 episodes of nasal catarrh) in the first year of life were associated with any wheezing (frequent and infrequent) between the ages of 1 and 4 years, but not with recurrent wheezing or asthma at 4 years of age.

CONCLUSIONS

Our results suggest that among children with a parental history of atopy the protective effect of day care attendance in early life against the development of atopy has begun by 2 years of age, and that a protective effect of day care attendance in early life against wheezing may not be observed until after 4 years of age.