REVIEW OF CHILDREN’S HEALTHEPIDEMIOLOGY COHORT STUDIESCAROL H. CHRISTENSEN, PH. D., MPHEPIDEMIOLOGISTUSEPA, OFFICE OF PESTICIDE PROGRAMSApril 10, 2012FIFRA SAPBackground and HistorySeptember 2008 EPA presented targeted review ofthree children’s health cohort studiesFIFRA SAP Report:“Chlorpyrifos likely played a role”Cannot conclude “chlorpyrifos is the sole contributor” due toother co-exposuresHowever, epidemiology studies "should not beconsidered ...basis for characterization of PoD”Lack biologically plausible MOA, exposure uncertaintiesSupplemental analyses recommended2Background and HistoryApril 2012 EPA updates and expands its targeted review ofthese data:New etiologic papersIntelligence Quotient (IQ)New methodological papersSocioeconomic status (SES)Exposure characterization and validationSupplemental analyses (unpublished) (Appendix 4)DraftFramework Analysis approachWorking toward WOE EvaluationPanel guidance regarding qualitative and/or quantitativeuse these studies in risk assessment3Overview of Cohorts4Columbia cohort (1998-2002)NYC, Dominican and African -American Mothers-Infant pairsCord Blood ChlorpyrifosValidation studies (air, maternal blood, urine, meconium)Mt. Sinai cohort (1998-2001)NYC, multi-ethnic (African American, Hispanic, White)Measured TPCy (fetal growth only) and DAPsPON1 genotype and phenotypeU of CA Berkeley Cohort (CHAMACOS) (1999-2002)Mexican-American, agricultural worker populationMeasured TPCy and DAPsPON1 genotype and phenotypeOverview of Cohorts5Three prospective birth cohorts to examine environmentalexposures and adverse health outcomesChlorpyrifos/OP studies focus of this reviewBirth outcomesNeurodevelopmentEnrolled women during pregnancy, follow children throughtime, multiple measuresChildren’s Environmental Health and Disease PreventionResearch Centers (funded by EPA and NIEHS)Population CharacteristicsSought prenatal care (<20-26 weeks)Residency requirementDeliver participatinghospitalsNo diabetes, hypertension,HIV, history birth defectsNo smoking, illegal druguseMulti-ethnic populations:African-American,Dominican, Hispanic,Mexican-American, WhiteYounger mothers, ~25yearsLow prevalence risky healthbehaviors, co-morbidities(criteria)6General EligibilityCohort CharacteristicsExposure Measurement, Confounding Adjustment,Statistical AnalysesMethods and Analysis7Exposure Assessment8Cohorts differing exposure profiles, pathways, routesInner-city, agricultural and both residential, occupationalMultiple biomarkers reflect different windows of exposure:Chlorpyrifos in cord blood (Columbia)TCPy in urine (each cohort)DAPs in urine (CDC methods) (Mt. Sinai, CHAMACOS)TCPy meconium (validation study) (Columbia)AChE and BuChE in cord blood (CHAMACOS)PON1 genotype and phenotypeChlorpyrifos in air (validation study) (Columbia)Self-report questionnaire (each cohort)Exposure Assessment9Ideal MeasuresEstimates exposure during critical window of susceptibilityRepeat samplesperiodicity, variability of exposureReflective of true rank of actual exposureTiming of sample collection with applicationActual MeasuresOne-time, or average of two samplesThird trimester (unknown window of effect)Specific and non-specific biomarkers of chlorpyrifosAdapted D. Savitz 2002Exposure Measurement Error10External exposure versus measured internal doseReflects total exposure (all routes)Single measure, third trimesterTemporal-spatial patterns of exposure unclearExposure during critical window of developmentLikely third trimester importantMissing exposure dataImputation methods, dataLaboratory errorsExtensive QA/QC measures, CDC laboratoriesExposure Validation Study11Questionnaire Data:85% report use pesticide, most report at leastmonthly useEvidence consistent use prior to 2000External DataNYC Housing Authority reported useTotal usage in NYC housing greater than NY state Ag usesprior to voluntary cancellationExposure Validation StudyAir monitoringLast 8-wks, stationaryairPersonal (48-hr) andIntra<inter variabilityBiomarker Collection:Maternal UrineLast trimesterAt deliveryMaternal bloodMeconiumNeonate urineCompare Cord bloodEtiologic measure12Period of RapidDecline of UseWhyatt et al. 2007, 2009Exposure Validation Study13FirsttrimesterMeconium week14 thrudeliverySecondTrimesterThirdTrimesterWeek32 thrudelivery:bi‐weeklyairmonitorandmaternalurinesampleWeek32(pilot):48hr.airWeek14Week24ConceptionWeek14Week20Cord blood,meconium,maternal urineCord BloodExposure Validation Study14Cord Blood Measures Correlate with Meconium (exposure period)Whyatt et al. 2009Exposure Assessment15Uncertainties RemainLimited window of exposure measuredOne-time measure (Columbia, Mt. Sinai)CHAMACOS averages two exposuresValidation studies suggest some degree of correlationUnknown periodicity of exposurePeaks, constantPrevalence of pesticide exposure highMedian concentration TCPy within range of generalpopulation (NHANES)May indicate difference actual and measuredMethods to Control ConfoundingRestriction (design)Through recruitment techniques, similar populationcharacteristicsStatistical Adjustment (individual-level)Race, education, income, housing qualityTested for statistical interactionMultilevel Model (SES, Columbia only)Account group-level and individual-level variability16Methods to Select PotentiallyConfounding VariablesMethodsSearching literature, other studies in areaTested univariable and multivariable modelsIncluded if observed +/- 10% change in estimateEvidence of statistical confoundingForward/Backward step-wise selection proceduresInclude if known risk factorEvidence of biological confoundingMany known or suspected confounding variablesmeasured and modeledEmphasis on Parsimony17Confounding VariablesDemographicHealth-relatedEnvironmentalexposures PAH, ETS,DDT/DDE, PCB,OC/HCBPostnatal environmentOther environmentalchemicals: Lead, Mercury,Diazinon, PropoxurSocio-economic statusIn general, challenging tomeasure18General FactorsMajor Potential (residual)Confounding VariablesWhen Confounding Bias?*Personal Communication R. Whyattρ<0.20 – likely no effect0.20<ρ<0.40 – little chance0.40<ρ<0.60- some effect0.60<ρ<0.80 – strong effectρ>0.80 – collinearityND OutcomesConfounderCPF Exposure19Lead, Mercury*correlation <0.10Confounding: Other OPs20Effects of Chlorpyrifos on the odds of Mental Development Delay on the BayleyScales of Infant Development at age 36 months. (βcoefficient, 95% CI, p-value)Model 1Model 2Model 3Model 4Chlorpyrifos22.3 (1.1, 5.2)p=0.033.8 (1.5, 9.4)p=0.0042.0 (0.9, 4.5)p=0.113.2 (1.3, 8.2 )p=0.02(ln)Diazinon0.57 (0.35,0.95)p = 0.030.6 (0.3, 0.9)p=0.03(ln)2-isopropoxyphenol(propoxur)1.5 (0.9, 2.5)p=0.121.5 (0.9, 2.6)p=0.11Appendix 4: Whyatt and Rauh, 2011 (unpublished)SES: Multilevel AnalysisThe study of the effects of collective or groupcharacteristics (as well as individual ones) onindividual-level outcomesNot all associations explained by individual levelcharacteristicsGroup-level variables may affect individuals directlyand also constrain the choices that individuals makeImprove accuracy and precision of statistical modelsinclude Groupand Individuallevel21SES: Multilevel Analysis (cont.)Group levelvariablesIndividual level variablesCPF estimatesLovasi et al. 201022Statistical Analysis23Statistical modeling decisions appropriate to theresearch question, characteristics of data etc.Missing data, <LOD(imputed, sensitivity analyses)Sample size adequate main effectsLikely under-powered for effect modificationSensitivity analyses to evaluate alternativemodeling optionsFetal Growth, Neonatal NeurologicalDevelopment, Infant Motor and MentalDevelopment, Attention Disorders, IntelligenceMeasuresResults24Fetal Growth and Characteristics25Authors hypothesized link between pesticide andeffects on fetal growthHypothesized link to neurodevelopmentMedical record linkageBirth weight, length, ponderal indexGestational age, preterm birthsHead circumferenceEffect modification evaluatedPON1 genotype and phenotypeFetal Growth and Characteristics26ColumbiaCohortMountSinaiCohortUofCABerkeleyCohortMarkersofExposure:ChlorpyrifosTCPy (fetalgrowth)TCPyDAPSBirthLengthInverse(Nullpost2000)NullPositive(n.s.)PositiveBirthWeightInverse(Nullpost2000)NullPositive(n.s.)NullHeadCircumferenceatBirth‐‐Null(Inverse(NS))*NullPositive(Inverse*)GestationalAge‐‐NullNullNull(Inverse*)* PON1 genotype or phenotypeNeonatal Neurodevelopment27Brazelton Neonatal Behavioral Assessment Scale(BNBAS)Goal: provide information parents/caregivers28 behavioral items-habituation, range of state,orientation18 primitive reflexesAssessed 2-5 days post-partumTrained neonatologists administeredHospital settingNeonatal Neurodevelopment28Consistent,reflexesOutcomemeasure goodqualityDAPs only,limitationColumbiaCohortMountSinaiCohortUofCABerkeleyCohortExposureMeasureCPFDAPSDAPSBNBAS(Abnormalreflexes)‐‐Positive*PositiveBNBAS(OtherBehavioral)‐‐NullNull* PON1 genotype or phenotypeInfant Neurodevelopment29Bayley Scales of Infant Development IIMental development index (MDI)Psychomotor development index (PDI)Measured 6-36 monthsHigh reliability and validity as screening tool for early interventionChild Behavior ChecklistDesigned to assess "social competence" and "behavior problems" in children(Maternal report)Race/ethnicity small proportion of score variance99-item questionnaire to ascertain behavior and/or attentionalHome Observation Measurement of the Environment (HOME)Stimulating environment for child developmentEffect modification evaluatedPON1 genotype and phenotypeInfant Neurodevelopment30ColumbiaCohortMountSinaiCohortUofCABerkeleyCohortMarkersofExposure:ChlorpyrifosDAPSTCPyDAPSBayley Scores6months(MDI/PDI)‐‐‐‐Null/NullInverse(NS)/NullBayleyScores12months(MDI/PDI)Null/NullInverse(*/**)/null(NS)Null/NullNull/NullBayleyScores24months(MDI/PDI)Null/NullInverse(n.s.)/NullNull/NullInverse/NullBayleyScores36months(MDI/PDI)Inverse/Inverse‐‐‐‐*PON1 genotype or phenotype; **AmongblacksandHispanicsAttention Problems31Measurement ToolsCombination Maternal report and direct observationChild Behavior Checklist (maternal report)Direct Assessment of child (K-CPT)Hillside Psychometrician reportDSVM-IV ADHD symptomsAssessed at 3, 3.5 and 5 years in two cohortsAttention Problems32Sensitivity oftest at 3 yrslimitedConsistentresults , twodifferentexposuresPrenatal lead,lack postnatalColumbiaCohortMountSinaiCohortUofCABerkeleyCohortExposure:CPFDAPSDAPS(PDD)Positive(36mo.)‐‐Positive(24mo.)OddsofADHD/attentionproblemsPositive(36mo.)‐‐Positive(NS3years)Positive(5years)Intelligence Measures33Wechslar Intelligence Scale for Children IVVerbal comprehensionPerceptual ReasoningWorking Memory (WM)Processing SpeedFull Scale IQ (FSIQ)Standardized US population, norms English andSpanish speaking populationsCultural Bias has been notedRestricted sample populationIntelligence Measures34Consistent resultsacross studies(WM)Large numbermissing tests,include/excludecomparableColumbiaCohortMountSinaiCohortUofCABerkeleyCohortExposureCPFDAPSDAPSMentalDevelopment(WISC‐IV)Inverse(FSIQ,WM)Inverse(NS)(FSIQ,perceptualreasoning,WM)Inverse(FSIQ,WM,processingspeed,verbal,perceptualreasoning)DraftFramework AnalysisEvaluation and Synthesis35Strengths and LimitationsMeasurement outcome andexposure extensive, validated,reliableImportant confoundingvariables measured andmodeledDesign and analysisdecisionsaid comparability betweengroupsReduce manysources ofbiasPeer-reviewed publicationsUnknown factor may correlatewith CPFHowever, among known orhypothesized factors withpotential positive confoundingbias, lack evidence explainobserved associationsIn general, difficult to tease outSES in any epidemiology studyRestriction, individual and grouplevel multi-variable analysis (R2moderately high)Role of postnatal environmentLimited instances in whichmeasured, not confounder36StrengthsLimitationsStudy Design IssuesA priorihypothesesStatistical modelingappropriateDiscussed varyingdegrees across studiesMissing data imputedwhen possibleSelection CriteriaextensiveEnhance internal validityReduce external validity(generalizability)High prevalenceexposure, outcomeenhanced study powerLimited evaluation ofinteraction with otherchemicals,OPs37Statistical Analysis and GroupingSeveral Methods Used across studies:Motivated by sample size, study hypothesisGrouping straight-forward, fully explainedAnalysis issues not always discussed in fullSeveral sensitivity analyses performedQA/QC measuresAlternative hypotheses exploredModel fitting exercises, shape of data38Exposure Measurement39Chlorpyrifos (parent), non-specific (TCPy, DAP)Lack specificity, direct comparabilityMay explain heterogeneityUnknown temporal, spatial pattern of exposureConstant, intermittent, and/or sporadicOne-time measure correlated with longer-term markerMeconium=maternal urine (ave.)=cord bloodCohorts’ exposures greater than, but comparable topopulation medianGeneralizable to US populationOutcome Ascertainment40Outcome MeasuresSimilar, aids comparisonClinical, research settingsSpanish/EnglishQuality Assurance and Control adequateStated observers blinded in some, not all studiesLimitationsNeurodevelopmental assessments subjectiveCultural bias –Wechslar toolNon-differential error likelyMultiple exposure ameliorates potential differential biasConfounding Bias41Multiple methods of controlRestriction, individual- and group-level (SES)Cannot exclude possibility positive confounding biasof unknown factorLead, mercury, other OP, OC, PCB, PAHSESMulti-dimensional, both +/- confounding biasesHierarchal regression analysis utilized to assessLack examination of heterogeneity by otherenvironmental exposuresThreats to ValidityRetention ratemoderately high forbirth cohorts (60-80%at 7 years)Included and excludedcomparableMeasured variablesMissing Data imputedErrors in outcome andexposure measuresoccurredDesign reducesdifferential biasMany exposuresNon-differential mayhave reduced effectsizes42Selection BiasInformation BiasSynthesis of Evidence43Strength of observed associations high in somecases, but not allNon-differential exposure measurement error couldreduce magnitudeSome evidence of exposure-response in studiesConsistency in Brazelton (abnormal reflexes),ADHD-like behavior problems, Bayley (particularlyMDI), and IQ (WM)Alternative explanations investigatedModeling, transformations, confounding variablesSynthesis of Evidence44Prospective studiesTemporal relationDifferential misclassification less likelyBiological plausibilitySee other sections, generally plausible, lack specificdetails MOAInfluence of cessation of residential exposure onassociationLimited evidence (lowpower), not designed to assessConclusions45Current database strengthens conclusion 2008“chlorpyrifos likely plays a role” in observedadverse effects on child neurodevelopmentGiven study conduct, design, methods EPA believesmore likely under-thanover-estimate associationsIntegration across streams of information willcontinueSection 4.0Appendices 4-6Questions46Appendix 4: Supplementary AnalysesColumbia U. CohortBoundingSee Hattis PBPKHow many “LBW?”Not designed toaddressBayley ScoresExpanded two to fourcategories, highestcategory greatest riskLoss to follow-upNon-differential byexposure group (4)Pre-cancellationclarificationExposure level declineConfounding analysisDiazinon, propoxur47