MISCELLANEOUS Principles of public health surveillance: a ... · urge public health action for...

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Journal of Public Health and Development Vol. 13 No. 1 January - April 2015

MISCELLANEOUS

Principles of public health surveillance: a revisit to fundamental concepts Chanapong Rojanaworarit, Ph.DDepartment of Epidemiology, Faculty of Public Health,Mahidol University, ThailandEmail:[email protected]

Abstract

Theobjectiveofthisarticlefocusesonfundamentalconceptsofpublichealthsurveillance,especiallytograduatestudentsandhealthprofessionalswhoarenewto thisdiscipline.Thearticle initiallyexplainshowconceptsofsurveillanceinpublichealthhaveevolvedover theperiodofsixdecades.Thenthe threemajorobjectivesofsurveillancearefurtherdiscussedindetail.Withclearspecificationoftheobjective,surveillancesystemcanbeestablishedtofulfillthegoal.Generalconsiderationsforestablishingnewsurveillancesystemare thereforeoutlined.Methodicalprocessof surveillance from informationgeneration to the link topublichealth actions is thoroughly explained.Challenging issues and current technical advance in this field ofepidemiological practice are additionally summarized.

Keywords: public health surveillance, epidemiologicalmethod, public health, disease control

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วารสารสาธารณสุขและการพัฒนา ปีที่ 13 ฉบับที่ 1 มกราคม - เมษายน 2558

Introduction Fromtheearlyconceptofsurveillanceconcentra-

tingondetectionofsuspectedactofcrimecommis-

sion,conceptionofsurveillancehaslaterbeenadopted

intomonitoringdiseaseoccurrenceinindividualsand

progressively evolved into the current concept of

ongoingobservationonacertainpopulationtogauge

thechange indefinedhealtheventand todetermine

whether a public health act is promptly needed for

controlorpreventionofthealteredhealthcondition.

Since the global trend of disease has shifted in

termsof burden from infectious diseases to chronic

non-communicablediseases,methodofpublichealth

surveillance has thus been developed in response

to this change. From the conventional surveillance

approach,which concentrates onmeasuring disease

occurrence(e.g.,numberofcaseswithacertaindisease)

and related consequence (e.g.,mortality); extension

toincludeobservationofriskfactors,environmental

hazard,andpositivehealthdeterminants–whichprecede

theoccurrenceofdiseaseorhealthoutcome–hasbeen

made for comprehensive care of population health

with amorepreventiveorientation.

This article focuses on fundamentals concepts

ofpublichealthsurveillanceimportantlyintermsof

its conceptualization andmethodological principles.

Conceptualdevelopment,objectives,generalconsid-

eration for surveillance system establishment, and

currentmethod of public health surveillance are

discussedindetail.Challengingissuesandtechnical

advance in practice of surveillance are additionally

summarized. The aim of this article is to provide

general overview of this epidemiological practice

especiallyforgraduatestudentsinepidemiologyand

healthprofessionalswhomaynotbe familiar to the

discipline.More technical advance in this evolving

fieldof public health surveillance,whichmaybe far

beyond the scopeof this article, can alsobe further

exploredwith the prior foundationprovidedherein.

1. Defining and conceptualizing ‘surveillance’:

frometymologicalbasistocontemporaryrecogni-

tion inpublichealth

‘Surveillance’–aFrenchword inoriginbelieved

tobeadoptedintoEnglishin1802–isanounsimply

defined as ‘the act of oversight orwatching over’.

Thetermcomprisestwowordelementsincluding‘sur’

(overoratop)and‘veiller’(towatch).1‘Surveillance’

was introduced intoEnglish from terror in France

where ‘surveillance committees’were established

in allmunicipalities in 1793 tomonitor the act of

suspected individuals.1

Surveillancewas initially acknowledged as the

act of closemonitoring of individuals exposed to

contagious or communicable diseases for timely

detection ofmanifestationswhich further indicated

controlmeasures–such as quarantine.2Until 1950,

perspective change in surveillance from the act of

individualmonitoringtopopulation-basedsurveillance

ofdiseaseoccurrence.2Thisapproachbecamepromi-

nent following the 1954field trial of poliomyelitis

vaccine(Salk’sinactivatedpoliovaccinetrial)inthe

US.3Populationsurveillancehasalsobeenapproved

asanintegralresponsibilityofpublichealthpractice.4

The approach comprised three fundamental

featuresincludingsystematicdatacollection(atlocal

sources),dataassemblyandanalysis(atsurveillance

centers), anddisseminationof pertinent information

and precisemessage through descriptive epidemio-

logical reports.5

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The notion of extending role of surveillance to

indicate control activitieswas also considered.6 In

someWHOprograms,informationfromsurveillance

hasevidentlybeenapplied tospecifyingactivecon-

trolmeasures–such as extensive vaccination against

smallpox.6Nonetheless, this concept of using the

information from surveillance to determinewhat

activitytobeimplementedwaslaterobjected.6Ithas

beensuggestedthatsurveillanceshouldonlybeahint

of feasible control activitieswhile health authority

should retain the right tomake decision regarding

practical controlmeasure to be implemented in the

actual context.6This suggestion ismore relevant to

the actual context of public health practice since

healthresourcesandcontextualconstraintsaretaken

into consideration, anddecision to act inwhatway

can be justified by local health practitionerswho

understand local circumstancewell.

Other terms including ‘epidemiological surveil-

lance’and‘publichealthsurveillance’havealsobeen

proposed. The term ‘epidemiological surveillance’

was broadly defined as ‘epidemiological study of

disease–even incorporating epidemic investigation

and research–as a continuous and ever-changing

process’.2Nonetheless, this definitionwas opposed

based on the reason that it seemed equivalent to

how epidemiological practice has been defined.2

Even though surveillance datamay reveal gap of

knowledge and hypothesis formulation leading to

research,objectiveof research isdifferent from that

ofsurveillanceandshouldberecognizedseparately.7

ThackerandBerkelmanthuslaterproposedtheterm

‘publichealthsurveillance’whichconservedbenefits

of the initial term ‘epidemiological surveillance’

while excluding confusionwith research.2 Public

healthsurveillancehasthusbeendefinedasasystem

comprising continuousdata collection, data analysis

and interpretation,disseminationofkey information

andmessage to the responsible personnel to timely

urgepublichealth action for control andprevention

of disease or condition.8 Public health surveillance

does not incorporate specification of preventive and

controlmeasures.Publichealthsurveillanceisaimed

essentiallyatprovidinghintofapplicablecontroland

preventive activities. In otherwords, public health

ratherprovidesinformationofpublichealthsituation

forresponsiblepersonnelatalllevels,guidesfeasible

programs, and later eases programevaluationwhen

outcomes are assessable.8 For further discussion in

this article, the term ‘surveillance’ refers to ‘public

health surveillance’. Summaryof conceptual devel-

opment of surveillance andmajor characteristics at

each stage is provided inTable 1.

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Table 1 Summaryofconceptualdevelopmentofsurveillanceateachstageandcorrespondingkeyfeatures

Conceptualdevelopment

Unit ofobservation

Health eventofinterest

Key features

1)Personal surveillance (Individual monitoring)

2)Disease surveillance

3)Epidemiological surveillance

4)Public health surveillance

• Individual

• Population

• Population

• Population

• Disease(especiallyinfectiousdisease inman)

• Disease (communicable and non-communicable)• Other health problems (e.g., environmental hazard)

• Disease• Other health problems

• Disease• Other health problems• Unusual event (e.g., mass animal death)• Riskbehavior• Variousother conditions

• Closemonitoringofindividualsuspectedof havingdisease

• Detectionof disease symptom• Informationisusedforindicatingcontrolmeasure such as quarantine.

• Ongoingobservationofhealtheventwithorganizedprocess

• The process comprises data collection,assembly, analysis and interpretation.

• Extendedscopeofsurveillancetoincludeepidemic investigation and research

• Theconceptwasobjectedsinceitmisledunderstandingofsurveillancepracticetobeequivalenttoepidemiologicalpractice.

• Organized systemcomprisingdata collection, analysis, interpretation, disseminationofinformation,andlinktopublic health action

• Information isusedfordecisionmakingrather thandictatewhat action to take

Although ‘surveillance’ and ‘monitoring’ seem

similarinmeaning,thesetermsareactuallydifferent

andshouldnotbeusedinterchangeably.Monitoring

resemblessurveillanceinthatitsmethodalsofocuses

ontimeliness,practicability,andcontinueddatacol-

lectiononroutine.2Nonetheless;surveillanceallows

impactassessmentofdiseaseinacertainpopulation

prior to and following implementation of health

program,whilemonitoringfocusesonlyonevaluating

post-implementationoutcomes.2Theotherdistinction

of these terms isaccording to theirgroupsof focus.

Surveillance focuses on relatively larger group of

populationswhilemonitoring commonly concerns

individuals(e.g.,monitoringofvitalsignsinacertain

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patient)orspecificgroups(e.g.,effectivenessevalua-

tionofHIV/AIDSpreventiveprograminfemalesex

workersormonitoringoflong-termglycemiccontrol

amongdiabeticpatientsattendingadistricthospital).2

Theother difference to be remarked is between

‘surveillance’and‘survey’.Whendataarenotreadily

availableinroutinedatacollectionofexistinghealth

servicesystem–asthatcommonlyfoundinsurveillance,

suchdataarethenspecificallycollectedforacertain

reason or objective in an organized way called

‘survey’.9Therefore,intermsofhowsurveyisrelated

to surveillance, survey can be one of the possible

methodsofobtainingdataforsurveillance.Nonetheless,

survey adopts active approach of population-based

data collection for a certain purpose;while surveil-

lance, in general, passively adopts readily available

dataofacertain facility.9Survey is thusundertaken

on occasion with specified value of budget and

invested resources;whereas surveillance is rather a

continued and less costly process in the long run.9

Surveillanceusuallyinvolvesallhealthagenciesfrom

local health facilities to health authorities of higher

levels: provincial, national, international.2Theflow

of information is usually in back and forth pattern:

upwarddata reporting, downwardpolicy suggestion

for action, upward report on effectiveness of policy

implementation,downwardfeedbackandsupport,and

others.Unlike surveillance, survey is occasionally

fundedforspecifiedobjectiveanditsresult israther

directed to fundingprovider or concerned agency.9

2. Objectives of surveillance Ingeneral,thepurposeofsurveillanceistoidentify

changesindistributionortrendstolaunchinvestiga-

tionorcontrolactivities.10Tobemorespecific,three

major objectivesof surveillance canbe listed as (a)

todescribethedynamicpatternofdiseaseoccurrence

which links to public health action, (b) to elucidate

naturalhistoryandepidemiologicalprofileofdisease,

and(c)tosupplybaselinedataandrelevantinforma-

tion.2Theirfeaturescanbesummarizedasillustrated

inTable 2.

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Table 2 Objectives of surveillance and corresponding features

Objectives of surveillance Key features

1) Todescribe the dynamic pattern of disease and link to public health action

2)To explain natural history and epidemiological profile of disease

3)To supplybaseline data for planning and evaluationof health program

Descriptionof disease pattern is undertaken to:• detect immediate changes in disease occurrence anddistribution (e.g., disease outbreak, food poisoning),• identifydisease trendandpattern (e.g., increased incidence of ovarian cancer

in younger Thai women),• anticipatepossibilityofgettingdiseasebymonitoringchangeinhostoragent

factors (e.g., study of mutated pathogen), and• identify change in disease burden fromhealthcare practice (e.g., increasing number of patients requiring dental extraction).

Informationobtained from thedescription is used for:• decision to provide prompt action (e.g., identifying agent causing disease

outbreak and guiding control measure)• healthcare planning (e.g., focusing more on oral health prevention to control

the problem of tooth loss)• reorganizinghealth service system• evaluating effectiveness of the implemented program (e.g., effectiveness evaluation of vaccination program)11

• Aid in explaining natural course of a certain diseasewhich has not beenpreviously clarified

• Allowdescriptionof epidemiological profile of disease in termsof ‘persons’ being affected, ‘place’ or risk environment, and ‘time’

of disease occurrence.• Provide information for planningof control andpreventivemeasures• Allow estimation of impact from health program on target health outcome

prior to implementation (e.g., projection or predictive model development to anticipate effect of proposed health policy using disease trend data)

• Supply baseline data for comparison or evaluation of target health outcomeafter the health program is implemented (e.g., measuring marginal benefits after implementing health program)11

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3. General consideration for surveillance system establishment Establishmentofsurveillancesystemisappropri-

ate only for somediseases or health-related events.

This ismainlydue tohealth resourceconstraintand

additionalburdenonoperatingthesysteminthelong

run.Rationalselectionofdiseasesoreventseligible

to be put under surveillance is thus important for

system establishment planning. In general, diseases

or health events suitable for surveillance are those

potentiallycausingseverehealthoutcomes(e.g.,death,

disability,long-termsuffering).Examplesofdiseases

and conditions in this category aremalaria,HIV/

AIDS, tuberculosis, rabies, and hazardous chemical

exposure.12-15

Highly transmissible diseases and epidemic

or pandemic diseases of international concern are

also considered for surveillance.Examples of these

diseases areEbola16, hemorrhagic fever,measles17,

and influenza18. Some conditions or health events

are put under surveillance for evaluation of health

program implementation and related effectiveness.

Examplesinthiscategoryaresurveillanceofinfluenza

vaccinationcoverage19andevaluationofpoliomyelitis

vaccine efficacy infield trial3.

Inadditiontotheselectionofdiseasesorconditions

eligibleforsurveillance,thereareseveralotherrelated

issuestobeconsidered.Dataandinformationrequired

foranalysisandformulationofapplicablepolicyand

implementationmustbewellspecified.Therequired

datamust also be feasible in terms of collection

fromappropriate sources andquality ascertainment.

Regardingcostconsideration,benefitofsurveillance

for a certain event shouldoutweigh the cost burden

arises from its operation.Cost containment–control

ofexpensesaccordingtobudgetconstraints–isalsoa

criticalissueinfluencingsustainabilityofsurveillance

systemoperation, especially in the long run.

Box1. Considerations for establishing

surveillance system

• Health resource constraints (critical issue especially setting up system requiring long-term operation)

• Diseaseorhazard • causing severehealthoutcomes (e.g., rabies, radiation hazard) • highly transmissiblediseases (e.g. Ebola) • epidemics / pandemic (e.g., influenza) • diseaseoutcome indicating success or failure in evaluationof interventional effectiveness (e.g., vaccine efficacy trial)

• Feasibility of obtainingqualitydata • Cost containment

4. Methodical process of surveillance Methodical process of surveillance comprises

several consecutive steps including data collection,

data analysis, interpretation of analysis results,

dissemination of information, and link to public

healthmeasures.Detailsofthesestepsareexplained

as followed.

4.1 Data collection

Data collection is themost critical phase of

surveillanceintermsofthegreatestamountofbudget

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toinvestanddifficultyinobtainingqualitydata.Data

for surveillance primarily vary according to ‘health

events’ofinterest.Dataregardingsomeeventscanbe

obtainedthroughpopulationregisterorvitalstatistics

system(e.g.,mortality,cause-specificmortality,infant

mortality).20 Some events are recorded on routine

medicalpractice(e.g.,maternalandneonataloutcomes,

congenital defects, communicable diseases, chronic

diseases,mental illness, health practice, nosocomial

infection,surgicalsiteinfections21).Surveillanceisnot

only limited to detection of health problemonce it

occurs,butitsrangeofdatacanalsobeextendedto

include factors influencing the health problemprior

toitsoccurrenceormanifestation.22Theseinfluencing

factorscanbehealthriskbehaviors22,environmental23

andoccupationalhealthhazards24,foodcontamination,

diseasevectors,animal reservoirs,andothers.Some

eventsareshort-termconsequencesofcatastropheand

thesecanbetemporarilyputundersurveillanceuntil

the disaster is resolved. Examples of these events

areoccurrenceof infectiousdiseases, injuries,effect

onmental health, anddemandofmedical care after

earthquakeandtsunami.25,26Otherunusualeventscan

alsobenotified through tourgeprompt information

capture,assessmentofpotentialrisktopublichealth,

andimmediateactionifrequired.Examplesofthese

eventsareclusterofdisease,deathsofunidentifiable

cause, atypically severe case,mass animal deaths,

andmigrationofwild animals.

Surveillanceofsomediseasescanbeundertaken

atdifferentstages; rangingfromsurveillanceofrisk

behaviors,subclinicalstages,clinicalevents,treatment

outcomes,andtoultimateconsequenceofrecoveryor

death.An example of diseaseswith comprehensive

surveillance system isHIV/AIDS.27 Surveillance of

HIV/AIDScanbe commenced from surveillance of

riskbehaviors.HIVsero-surveillanceisconductedto

determineHIV infection in laboratory investigation,

early before the disease clinicallymanifests.HIV

cases–classifiedbydifferentcasedefinitionsforsur-

veillance–arereportedonroutinepatientcareservice

to reflect burdenof the disease and for planningof

patientcare(e.g.,multipleantiretroviraldrugsprovi-

sion).Drugresistancesurveillanceisalsoanintegral

partofHIV/AIDSpatientcareandfrequencyofreport

primarilydependsonlevelofinfectionandavailable

healthresourcesforconductingthisperiodicsurveil-

lance.

Numerous sources of data can be adopted for

publichealth surveillance.Variationofdata sources

isonaccountofseveralfactors;includingavailability

andaccessibilityofdata(e.g.,routinely-collecteddata),

budgetconstraint(e.g.,fundingforspecialeffortofdata

collection), characteristics of health service systems

(e.g., cooperationofpublicorprivatehealth service

providers), quality and availability of facility (e.g.,

laboratoryfacilities,computernetwork),andperson-

nel(e.g.,medicalspecialistsverifyingcasebasedon

surveillance case definition).2To specifywhat data

are needed, objective of surveillancemust be first

considered.Theobjectiveofsurveillancewouldguide

whichdataarerationaltobecollected–priortocheck-

ing feasibility toobtain thedata inpractical setting,

specifyingdatacollectionapproach,andanticipating

action to be recommendedby surveillance informa-

tion. For instance, if the objective of surveillance

is to detect a foodborneoutbreak, evidences related

to the suspected outbreak (e.g., abrupt increase in

numberofpatientsdiagnosedwithacutegastrointes-

tinaldisease,typeoffoodsharedincommonamong

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cases)areneeded.Approachofdatacollection(e.g.,

active surveillance approach to directly collect food

specimen for laboratory investigation of causative

agent) can then be specified. Surveillance data

and their corresponding sources are exemplified in

Table 3.

Table 3 Surveillance data and corresponding sourcesor settings of data collection

Surveillancedata Sources or settingofdata collection

1. Mortality data2. Morbidity data

3. Data for epidemic detection

4. Data for laboratory surveillance

5. Data for analyzingdisease occurrence and risk factors

6.Data for healthcare andhealth system surveillance

7.Environmental data

Death registrywith recordof accurate causeof deathCase reporting (from routinemedical service),Individualcasereport(e.g.,casereportofraredisease,caseofemergingdisease,usual variant of commondisease),Compulsory report of casefindingby legal regulation for somediseases(e.g., cholera,Ebola hemorrhagic fever)Epidemicfield investigation,Cluster of illness reportedby community-based surveillance,Findingof unusual event (e.g., cluster of animalmass deaths)Serological survey,Laboratory report forHIV sero-surveillance,Laboratory identification of etiologic agent for diagnosis of a certain diseaseRecordof demographic data,Riskbehavior survey,Findingof disease vector or animal reservoirMedical care statistics,Record fromcooperative networkof health professionals,Recordof specifiedhealth indicators,Recordof specified administrative dataWater quality assessment,Measurement of hazardous chemical exposure in factory

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There are five data collection approaches in

surveillance including passive surveillance, active

surveillance,sentinelsurveillance,community-based

surveillance,andsyndromicsurveillance.Keyfeatures

of these approaches are summarized inTable 4.

Data collectionapproaches insurveillance

Key features

1)Passive surveillance

2)Active surveillance

3)Sentinel surveillance

4)Community surveillance

5)Syndromic surveillance

• Data reportedbyprovidersworking in routinepractice• Aim tomeasuremagnitudeof health problems• Economical and likely to be sustainable in a long run• Obtain only the data of individuals utilizing facility• Data canbeused as baseline for further considerationof additional active surveillance.• Directdatacollectionfromoriginalsourcebypersonnelinsurveillancesystem

themselves of a certain objective• Aimtoprovidebetterestimateofprevalenceorburdenofdiseasefromcases

living in a specified community.• Requiremore budget, time, personnel, and other resources to conduct than

required for passive surveillance• Preferablyperiodical undertaking• Data specifically collected for analysis of disease pattern• Focusondataofacertainsubgroupratherthanthewholepopulation,acertain

catchment area, or a certain disease factor• Canbe either passiveor active surveillance (dependingon the role of surveillancepersonnel in data collection)• Community residents act as data collector.• Report of unusual event or outbreak in community and further urge investigation.• Notablyuseful for initiation of outbreak investigation• Focusondataofclinical syndromeoccurringbeforecompleteprogression to

disease status,or signsandsymptomsoccurringprior todiagnosisofdisease• Some signs and symptoms canbeput under surveillanceprior to certain diagnosis of disease.Examples of syndromeput under surveillance are Influenza-like illness (ILI) andAcuteFlaccidParalysis (AFP).

Table 4 Data collection approaches in surveillance and correspondingkey features

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4.2Dataanalysis

Data analysis approach in descriptive study is

usuallyadoptedforanalysisofsurveillancedata.Typical

aimof analysis is to revealmagnitude, pattern, and

trend of a certain health problem.To achieve this

goal, data are analyzed to primarily identifymag-

nitude using appropriate indicator for health event

of interest. Prevalence is a commonmeasurement

ofmagnitude in caseofnon-communicabledisease.

Incidencecanalsobeofchoicetoidentifymagnitude

incaseof injuryandcancer. Inaddition to identify-

ingmagnitudeofproblem,pattern and trendcanbe

analyzedbyperson(personatrisk),place(riskarea),

and time (time at risk).

Affectedgroupofpersons,orthe‘person’element,

is generally describedbydemographic factors (e.g.,

age,gender,socioeconomicstatus).Othercharacter-

istics can also be described, based on objective of

surveillance.These characteristics are, for instance,

presenceofriskfactor(e.g.,smokingstatus),presence

of protective factor (e.g., history of immunization),

underlying systemic disease, and personal hygiene

practice (e.g., toothbrushinghabit).

The ‘place’ element of analysis is geographical

analysis in relation to the health event.Urban and

ruralareasaredifferentintermsoflivingenvironment,

population density, availability and accessibility to

healthfacility,andseveralotherconditions.Geographi-

cal analysiswould additionally provide information

on area-specific factorswhich potentially influence

health anddisease in residentsdwelling in the area.

Specifyingcatchmentareaofinterestwouldalsoallow

measurement of disease frequency (e.g., prevalence

andincidence).Diseaseoccurrenceonly inacertain

placewould imply risk areawhich further urges

investigationof area-specific factorwhich influence

suchoccurrence.

Analysisof‘time’elementisalsoimportantsince

natural course of disease requires time period to

progress(e.g.,inductionperiodfornon-communicable

disease occurrence and incubation period for infec-

tiousdisease).Moreover,dynamicchangeofdisease

occurrencecanbeobservedovertime.Therearefour

time trends commonly analyzed in epidemiology;

including secular trend, seasonal pattern, cyclical

trend,andepidemicdiseaseoccurrence.2Analysisof

health eventover a longperiodof time (e.g., years,

decade) is recognized as ‘secular trend analysis’.

Graphicaldisplayofdataisusuallyappliedtoreveal

how occurrence of the health event in a defined

population changes over the long observed period.

‘Seasonalpattern’ canbe revealedwhenoccurrence

of health event exhibits a certain seasonal pattern.

Denguehemorrhagic fever is anexampleofdisease

with seasonal variation in terms of transmission.

‘Cyclical trend’ can be analyzed for health event

hypothesized to have cycle of occurrence or repeat

a certain pattern again and again overtime.An ex-

ampleofhealtheventwithcyclical trend iscyclical

vomitingsyndrome.‘Epidemicdiseaseoccurrence’is

characterizedbydiseaseoutbreakordiseaseoccurrence

whichexceedsregularlyexpectedoccurrencerate in

a particular period of time. The outbreak of acute

foodbornegastrointestinaldiseaseinOswegoCounty

is a classic example for the epidemic occurrence of

disease.28Elements in analysis of surveillance data

canbe summarized in the followingBox2.

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Box2.Elements inanalysis of surveillancedata

• Measuring ‘magnitude’ ofproblem

(using epidemiological measurements–incidence and prevalence)

• Descriptionofpatternand trend

• Analysisby ‘person’ characteristics

• Age (e.g., disease incidence by age)

• Gender (e.g., lung cancer risk behavior by gender)

• Ethnicgroups (e.g., incidence of Tuberculosis among different ethnic group in the USA)

• Marital status (e.g., cervical cancer incidence among single and married women)

• Occupation (e.g., symptoms indicating pesticide exposure among chili farmers)

• Socioeconomicstatus(e.g., malnutrition among children in low socioeconomic status families)

• Analysisby ‘place’ characteristics’

• International comparison (e.g., estimated numbers of HIV/AIDS cases among different Asian

countries)

• Intra-country comparison (e.g., comparison of infant mortality rate by regions in Thailand)

• Urban-ruralcomparison (e.g., incidence of diabetes mellitus by area of residence in Thailand)

• Localdistributionofdisease (e.g., spot map of dengue hemorrhagic fever cases in a certain

district)

• Analysisby ‘time’ characteristics’

• Timeonset (e.g., incubation period in infectious disease)

• Secular trend (e.g., twenty-year trend incidence and mortality of cardiovascular disease in the

United States)

• Cyclical variation (e.g., mode of occupational injuries by month)

• Seasonalpattern (e.g., seasonal pattern of dengue hemorrhagic fever)

• Point epidemic (e.g., foodborne outbreak)

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4.3 Data interpretation

Interpretationofsurveillancedataiscriticalsince

theinterpretationwouldfurtherleadtoconsideration

whether public health action is really needed.Key

issues in data interpretation is the identification of

accurate increase in disease occurrence–to a certain

extentthatextrapublichealthactionispromptlyneeded

to timely control or prevent the disease.2Observed

increaseindiseaseoccurrencecanbeconfoundedor

influenced by other factors. The observed increase

maybe due to the larger size of population inves-

tigated.2Disease screening campaign and improved

diagnostic techniquewith better sensitivity can as

well increase case finding.2Reporting system also

determine the number of case to be found.2 These

factors should be rationally ruled out beforemak-

ingconclusive interpretationofdata that thedisease

occurrence is actually increased.

Different epidemiological measures provide

different information. Rational selection of these

measures to give an answer to a specific question

regarding situationof interestedhealthevent is thus

crucial.Epidemiologicalmeasurescommonlyusedin

surveillanceareincidencerate,incidenceproportion,

period prevalence, point prevalence,mortality rate,

and case fatality rate.Thesemeasuresmust bewell

selected since they allowdifferent implications and

interpretationof themeasuresmust be scientifically

sound.

4.4 Data dissemination and link to public

healthaction

Major issue in surveillance data dissemination

is ‘who need to know?’. Since the primary aim of

surveillanceistoprovideinformationforpublichealth

action,authoritativehealthpersonnelwhorequirein-

formationfordecisionwhethertoactarethustheones

mustbeinformed.Thepatternofdatadissemination

fromlocalorsubsequent levels to thehigherhierar-

chies can be viewed as a ‘down-top’ dissemination

ofdata.Thisdirectionofdatadisseminationusually

link to public action in termsof ‘planned response’

or planning for control andpreventionof disease.

Nevertheless,thehealthpersonnelatsubsequent

levelsmust also bewell informed of the situation.

This is due to the fact that local personnelmust

provide ‘acute response’ in case that prompt action

is needed, such as the case of outbreak.Moreover,

implementationofpolicyatlocallevelsrequiresjudg-

ment and applicationwhich is relevant to the local

contextorsettingbythesepersonnel.This‘top-down’

dissemination of data and policy can also provide

feedbackand stimulate improvement in surveillance

datareportingatthelocallevels.Theoverallsystem

of surveillance can be illustrated in the following

Figure 1.

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5. Challenging issues and technical advancement in surveillance Practice of surveillance continuously evolves in

responsetothedynamicchangeinhealthanddisease

condition in population. From the early concept of

detectinginfectedcase,focusofmodernapproachin

infectiousdiseasesurveillancehasshiftedtoforecasting

futureincidenceoroutbreakwithadvancedtechniques

such asmathematicalmodeling.29,30 This approach

enablestimelywarning,preparationofhealthfacilities,

andpreparednessofprofessionalstoproperlymanage

abruptly increaseddemand.Nonetheless, challenges

in forecastingexist especially in termsofpredictive

accuracyof futureoccurrence.31

Surveillanceofemergingandre-emerginginfec-

tiousdiseases isanotherfieldwhich rapidlyevolves

in accordance with dynamic change in lifestyle

(e.g., drug abuse)32, altered ecosystem (e.g., land

Figure1Overall systemof surveillanceand link topublichealthaction

use, deforestation, pesticide use)33, food production

(e.g.,EscherichiacoliO104:H4contamination)34,and

globalization (e.g., Ebola pandemic)35. Since the

disease emergence is influence by various factors,

interdisciplinarycollaborationandapplyingmultiple

strategies to strengthen corresponding surveillance

system can be a solution. ‘One health’ disease

surveillance,forexample, isanapproachcombining

expertise in several disciplines (e.g., veterinary and

environmental sciences) to control diseases (e.g.,

zoonoses).36Advances in laboratory-based surveil-

lancealsocontributetonearreal-timerecognitionof

outbreakincommunity.37Inresponsetoglobalization,

InternationalHealthRegulations(IHR)hasbeenestab-

lishedfor internationalcommunity toco-operatively

build up international surveillance systemwhich

timely detects, notify and response to public health

risks–such as surveillance in international airports.38

Policymaking for control andprevention

Acuteaction to control andprevent transmissionor

progression

13 � 1.indd 42 6/10/15 4:36 PM

43


Major challenges in implementing the IHR include

requirement of expertise and resource, governance,

international collaboration, andpolitical barrier.38

Surveillance of non-communicable diseases is

growing in its importance. Itsmodern paradigm

has shift towards health promotion and prevention.

With advances in causal research in epidemiology,

risk factors ofmany non-communicable diseases

havebeenrevealed.Suchknowledgefurtherenables

establishment of risk factor surveillance formajor

non-communicable diseases (e.g., cardiovascular

disease).39,40Behavioralriskfactorsarealsoofinterest

inmodernsurveillancesincemanynon-communicable

diseases are related to lifestyle and personal health

behavior.41

Conclusion The concept of surveillance has long been

developed from individual-based monitoring to

population-based surveillancewith organized sys-

tem to generate quality informationwhich links to

publichealthaction.Objectiveofsurveillancemustbe

specifiedprior to data collection since the objective

wouldindicatewhichdataareneededfortherequired

information.Varioushealtheventscanbeputunder

surveillanceandnotonlylimitedtodiseaseoccurrence.

Differentdata collection approaches canbe adopted

to suit the context of surveillance. In analysis of

surveillancedata,descriptiveepidemiologicalmethod

isimportantlyadoptedtorevealmagnitudeandpattern

ofhealthproblem.Longitudinaldatacollectionwould

additionallyallowanalysisoftrendofsuchproblem.

Informationobtainedfrominterpretationisprimarily

disseminated to those in need of such information.

Link to public health action can be either informa-

tion for prompt action or information for planning.

Since health and disease condition in population is

dynamic; practice of surveillance is also advanced

withmedical and information technology, and the

paradigmshifttowardspreventivehealthorientation.

Acknowledgement

Author wished to express deep gratitude for

Prof.Dr.JayantonPatumanond(FacultyofMedicine,

ThammasatUniversity) andMs. Jongkol Podang

(Senior lecturer, Faculty of PublicHealth,Mahidol

University)fortheirconstructivecommentsondrafts

of this article. This academic article is supported

byMahidolUniversity throughTalentManagement

Project to promote research activity.

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