Communicable disease surveillance : Strengthening the national perspective

T HE MASS VAC CI NA TION CAM PAIGNS IN CANADA, IN re sponse to an in crease in group C men in go coc cal men in gi tis in 199193 and the world re ac tion to plague in In dia in 1994, were sa lu tory re mind ers of the abil ity of in fec tious dis eases to pro voke wide spread pub lic and po liti cal con cern. Com mu ni ca ble dis eases re main the ma jor cause of mor bid ity in the world and are a lead ing cause of mor tal ity in de vel op ing na tions. How ever, the de clin ing in ci dence of many of these dis eases in Can ada and other de vel oped na tions, al lied to im prove ments in so cial con di tions, popu la tion health status and child hood im mu ni za tion prac tices, and the ad vent of an ti bi ot ics, has cre ated high pub lic and po liti cal ex pec ta tions con cern ing our abil ity to con trol com mu ni ca ble dis ease. Suc cess has been achieved in sub stan tially re duc ing mor bid ity and mor tal ity due to such child hood dis eases as mea sles, diph the ria, po lio, per tus sis and mumps. Such suc cess sto ries are, how ever, coun tered by the per sis tence of sexu ally trans mit ted dis eases, as the most com mon re port able dis eases in Can ada (1), and res pi ra tory vi rus and en teric in fec tions, as ma jor causes of mor bid ity, in ad di tion to the emer gence of ‘new’ in fec tions such as AIDS and mul ti ple antibioticresistant mi cro or gan isms in clud ing, for ex am ple, mul ti ple drugresistant tu ber cu lo sis.

T HE MASS VAC CI NA TION CAM PAIGNS IN CANADA, IN re - sponse to an in crease in group C men in go coc cal men ingi tis in 1991-93 and the world re ac tion to plague in In dia in 1994, were sa lu tory re mind ers of the abil ity of in fec tious diseases to pro voke wide spread pub lic and po liti cal con cern.Com mu ni ca ble dis eases re main the ma jor cause of mor bid ity in the world and are a lead ing cause of mor tal ity in de vel op ing na tions.How ever, the de clin ing in ci dence of many of these dis eases in Can ada and other de vel oped na tions, al lied to improve ments in so cial con di tions, popu la tion health status and child hood im mu ni za tion prac tices, and the ad vent of an ti bi otics, has cre ated high pub lic and po liti cal ex pec ta tions concern ing our abil ity to con trol com mu ni ca ble dis ease.Suc cess has been achieved in sub stan tially re duc ing mor bid ity and mor tal ity due to such child hood dis eases as mea sles, diphthe ria, po lio, per tus sis and mumps.Such suc cess sto ries are, how ever, coun tered by the per sis tence of sexu ally trans mitted dis eases, as the most com mon re port able dis eases in Can ada (1), and res pi ra tory vi rus and en teric in fec tions, as ma jor causes of mor bid ity, in ad di tion to the emer gence of 'new' in fec tions such as AIDS and mul ti ple antibiotic-resistant mi cro or gan isms in clud ing, for ex am ple, mul ti ple drugresistant tu ber cu lo sis.
Con trol of com mu ni ca ble dis eases re quires ef fec tive mecha nisms for de tect ing as early as pos si ble the pres ence, or moni tor ing the ab sence, of in fec tions in the popu la tion; for pro vid ing up to date rele vant in for ma tion on dis ease trends to health pro fes sion als; and for pre vent ing, con trol ling and treating spe cific dis eases.Sur veil lance data are use ful at two distinct lev els.At the first level, usu ally lo cal, such in for ma tion should be able to iden tify changes in trends which, when nec -  1) Lev els of in fec tious dis ease sur veil lance in Can ada CAN J INFECT DIS VOL 6 NO 3 MAY/JUNE 1995 es sary, can be used to trig ger ac tion to con trol a prob lem.At the sec ond level, usu ally that of pro vin cial, ter ri to rial or fed eral gov ern ments, ac cu rate in for ma tion should con trib ute to policy mak ing and the plan ning of care, pre ven tion and con trol pro grams.

COM MU NI CA BLE DIS EASE SUR VEIL LANCE IN CAN ADA
The mecha nisms for the col lec tion of sur veil lance data relat ing to com mu ni ca ble dis eases by the Labo ra tory Cen tre for Dis ease Con trol (LCDC) cur rently take place at three lev els (Fig ure 1).Cen tral to these ac tivi ties is the col lec tion of ag gregate data for the 47 no ti fi able dis eases (Ta ble 1).Each ju risdic tion has pub lic health leg is la tion re lat ing to the re port ing of spe cific dis eases to pub lic health authori ties, and the list of no ti fi able dis eases var ies with ju ris dic tion (2).There is no statu tory re quire ment for re port ing at the fed eral level; however, a list of 'n atio nally' re ported dis eases is pro duced by con sen sus agree ment among pro vin cial and fed eral health authori ties through the Ad vi sory Com mit tee on Epi de mi ol ogy (3).Ag gre gated age and sex data for each dis ease are transmit ted monthly by most prov inces and ter ri to ries to the Bureau of Com mu ni ca ble Dis ease Epi de mi ol ogy at LCDC.These data are tabu lated quar terly in the Can ada Com mu ni ca ble Dis ease Re port (CCDR) and pub lished in an an nual sum mary as a sup ple ment to the CCDR.In ad di tion to the ag gre gated data some prov inces also re port more de tailed in for ma tion by case.
Com ple men tary sur veil lance ac tivi ties have de vel oped around these 'core' ac tivi ties to col lect more timely in for mation or population-based sta tis tics on spe cific dis eases or groups of dis eases.Sen ti nel sur veil lance is cur rently based on Im mu ni za tion Moni tor ing Pro gram AC Tive (IM PACT) and the Sen ti nel Health Unit Sur veil lance Sys tem (SHUSS).IM PACT is a hospital-based sys tem for moni tor ing immunizationassociated ad verse events and other con di tions in clud ing, at pres ent, Hae mo philus in flu en zae group b in fec tion, congeni tal ru bella syn drome, po lio, in fan tile spasm and acute flac cid pa raly sis.SHUSS is based on nine health units in eight prov inces and was cre ated to carry out tar geted sur veil lance within a de fined popu la tion base.SHUSS was de scribed recently by An der son (4).Disease-specific ac tivi ties are aimed, for ex am ple, at national sur veil lance of AIDS and the sur veil lance of hu man immu no de fi ciency virus-infected in di vidu als in some prov inces.Transmission-specific sur veil lance is aimed at no so comial infec tions (5) and res pi ra tory vi rus in fec tions.The lat ter re lies on the use of an in ter ac tive voice re sponse sys tem.By this mecha nism pro vin cial labo ra to ries re port weekly, dur ing the win ter, the num bers of speci mens ex am ined for in flu enza, res pi ra tory syn cytial, parain flu enza and some ad eno vi ruses, and the number that are posi tive.This sys tem per mits the timely col lec tion of data in di cat ing res pi ra tory vi rus ac tiv ity.The outer ring in Fig ure 1 re lates to the moni tor ing of re ports from the World Health Or gani za tion (WHO) and in di vid ual coun tries to iden tify spe cific dis ease is sues, which may be of in ter est to Can ada.
Other ma jor dis ease da ta bases in clude data col lected by Sta tis tics Can ada (eg, on tu ber cu lo sis) and hos pi tal discharge data col lected by the Ca na dian In sti tute for Health Infor ma tion.How ever, the use ful ness of data from these sources for the pur poses of na tional sur veil lance of com mu nica ble dis eases, in terms of time li ness, is more lim ited.
A va ri ety of mecha nisms are used for the dis semi na tion of in for ma tion based on data re ceived by LCDC.These in clude both elec tronic and pa per out put.The cur rent, rou tine out put is listed in Ta ble 2 and in cludes the twice monthly CCDR, which is avail able in both printed for mat and elec troni cally via a Faxlink serv ice and a bul le tin board sys tem (6).In ad di tion to the regu lar CCDR, oc ca sional and an nual sup ple ments re lat ing to spe cific is sues or tabu lat ing na tional ag gre gated data are

DE VEL OP ING THE NA TIONAL PER SPEC TIVE
The main jus ti fi ca tion for col lect ing data at the na tional level is to use such in for ma tion to de velop na tional poli cies and pro grams and to pro vide ad vice aimed at im prov ing public health through leg is la tion and pre ven tion and con trol programs while mak ing the most ef fec tive use of re sources.Thus, the use of sur veil lance data can fall un der one or more of the fol low ing ar eas.Iden ti fi ca tion and con trol of po ten tially se ri ous and epidemic dis ease: Sur veil lance ac tivi ties may iden tify un usual events, such as the re-emergence of old patho gens or oc currence of newly rec og nized or un usual patho gens, or in clude pro grams de signed to give early warn ing of com mon dis ease such as in flu enza.In this par ticu lar ex am ple, sur veil lance programs may need to in clude ac tivi ties de signed to col lect both rou tine disease-specific (labo ra tory) data as well as other in dica tors of dis ease ac tiv ity (eg, phy si cian con sul ta tions, sickness ab sence rec ords, pneu mo nia deaths).Pro grams in volv ing sur veil lance of dis eases with sea sonal or pe ri odic pat terns of in ci dence lend them selves to in no va tive approaches to moni tor ing and analy sis.These in clude the use of pre dic tive mod el ling and dis ease map ping tech niques.De vel op ment and im ple men ta tion of na tional pre ven tion and con trol ac tivi ties: Na tional dis ease sur veil lance has a great deal to of fer to pro grams re lated to the iden ti fi ca tion of risk fac tors and to the de vel op ment of health edu ca tion and im mu ni za tion pro grams.This is both in terms of jus ti fi ca tion, in clud ing eco nomic as sess ment of the costs and bene fits of such pro grams, and the se lec tion of dis eases and popu la tions for tar get ing.Moni tor ing and as sess ment of na tional pre ven tion and con trol ac tivi ties: Dis ease sur veil lance ac tivi ties are es sential to pre ven tion and con trol ac tivi ties as one ap proach to evalu at ing the suc cess, or oth er wise, of a pro gram or as sessing its prog ress.Care ful moni tor ing will fa cili tate tar get ing and re fin ing of na tional pro grams, and could re duce costs by allow ing re sources to be con cen trated and di rected to wards spe cific needs.Pub li ca tion of sta tis tics to aid lo cal, na tional and in ter national pri or ity set ting: Cen tral data col lec tion car ries a respon si bil ity to en sure that the data are use ful and avail able.These data should pro vide in for ma tion about the im pact of disease on the com mu nity and con trib ute to the de vel op ment of de ci sion mak ing strate gies.This pro cess in volves func tional re spon si bil ity at sev eral lev els, al though the bounda ries need not be rigid.Gen er ally, the col lec tion of raw data and the imple men ta tion of con trol ac tivi ties tend to be lo cal re spon si bili -ties, while the pro duc tion of in for ma tion and the de vel op ment of pol icy are cen tral func tions and may oc cur in Can ada at the level of pro vin cial and fed eral gov ern ment.Where global programs are in volved, there may be in ter ac tion with in ter na tional agen cies in pro vid ing na tional data and in im ple ment ing and moni tor ing global tar gets.
The time li ness and qual ity of in for ma tion out put is highly de pend ent on the time li ness and qual ity of the data re ceived.Qual ity here in cludes va lid ity, the re la tion ship of the sam ple to the popu la tion as a whole, the com pre hen sive ness of the data set in re la tion to the popu la tion rep re sented and the uniform ity of the da ta set in terms of the in for ma tion col lected.This raises is sues about the varia tion among prov inces over what is re ported, when it is re ported and the fre quency of report ing.Such varia tion may re flect real dif fer ences in dis ease in ci dence and/or bi ases in tro duced into the da ta sets; these may be both quan ti ta tive and quali ta tive (Ta ble 3).Al though it is de sir able to re move as many ar eas of bias as pos si ble, from a prac ti cal view point it may be of greater im por tance to be aware of what bi ases are there and how they in flu ence the data.Con tri bu tion to the in ter na tional sur veil lance of dis ease: As an ac tive mem ber of the world pub lic health com mu nity, Can ada en deav ours to sup port the global sur veil lance ac tivities of agen cies such as the WHO.Among oth ers, re spon si bilities in clude pro vid ing these agen cies with data on vari ous dis eases.Ex am ples of this in clude con tri bu tion to the WHO surveil lance of AIDS and in flu enza and par tici pa tion in the Pan Ameri can Health Or gani za tion mea sles elimi na tion pro gram.Can ada also made an im por tant con tri bu tion to the WHO response to the plague epi demic in In dia in 1994.Through the use of on go ing op era tional in for ma tion net works Can ada was able to as sist in the col la tion, analy sis and dis semi na tion of key in for ma tion to na tional and in ter na tional re sponse centres.

IS SUES THAT WILL IN FLU ENCE DE VEL OP MENT OF COM MU NI CA BLE DIS EASE SUR VEIL LANCE
A number of is sues re lated to the so cial, physi cal and biologi cal en vi ron ments in which we live can af fect dis ease preva lence and in ci dence in the com mu nity, the like li hood of ex po sure to new or un usual patho gens and our abil ity to respond to or treat in fec tion.Some of the most im por tant is sues are listed in Ta ble 4 and il lus trate the di ver sity of these fac tors.Changes in the so - • Uni form ity of da ta set cial en vi ron ment, for ex am ple, will in clude such de ter mi nants as changes in popu la tion size and struc ture, in di vid ual and na tional wealth, and so cial abuse in clud ing in jec tion drug use, al co hol ism and smok ing.For ex am ple, the popu la tion of Canada has dou bled from 14.0 mil lion in 1951 to 28.7 mil lion in 1991.More im por tant, how ever, was the in crease in the age of the popu la tion over this pe riod.While the pro por tion of people aged un der 15 years de clined from 30% to 20%, the propor tion of peo ple aged 60 years and over in creased from 12% to 16% and is likely to con tinue to in crease (8,9).The in evi table con se quence will be an in creas ingly older popu la tion with a grow ing number of eld erly peo ple sub ject to fail ing health.So cial and demo graphic fac tors may also in clude in creased in ter na tional con tact re sult ing from greater num bers of Ca nadi ans trav el ling abroad and to more ex otic lo ca tions, and increased im mi gra tion to Can ada from tropi cal ar eas (10,11).The re sults of en vi ron mental change may be more dif fi cult to pre dict but could in clude the ef fects of pol lut ants on health status and in creas ing con tact be tween in di vidu als and rare ani mal or insect-borne patho gens.Changes to the bio logi cal en vi ron ment may re sult in in creased ex po sure to new or reemerging patho gens, or to patho genic mi cro or gan isms that have de vel oped mul ti ple drug re sis tance, as well as the risk of op por tun is tic in fec tions in pa tients with de pressed im mune sys tems.

SUM MARY
The value of sur veil lance is eas ily un der es ti mated when dis eases are de clin ing.Ber kel man et al (12), writ ing about the Ameri can ex pe ri ence, re cently gave a timely warn ing that "False per cep tions that such threats had dwin dled or dis appeared led to com pla cency and de creased vigi lance re gard -ing in fec tious dis eases, re sult ing in a weak en ing of sur veil lance -the foun da tion for con trol of in fec tious diseases."In Can ada the cur rent strength en ing of fed eral in fectious dis ease sur veil lance mecha nisms through in vest ment must en able data to be col lected that are both more timely and rep re sen ta tive of the popu la tion, pro vide timely and appro pri ate analy sis to health pro fes sion als and pol icy mak ers, pro duce in for ma tion that is rele vant and ac ces si ble, and be ver sa tile enough to re act to chang ing needs.To achieve this re quires not only ap pro pri ate re sources but also a high degree of con sen sus among the ma jor in ter est groups, both profes sional and con sumer, as to what in for ma tion is col lected, the mecha nisms em ployed to col lect it and the use made of it.In this re spect LCDC has a re spon si bil ity to pro vide both the en vi ron ment to en cour age con sen sus and to fol low through in the de vel op ment and main te nance of ap pro pri ate pro grams.
of po ten tial bi asesQuan ti ta tive bias• Under-reporting• In con sis tent re port ing • Case carry-over Quali ta tive bias • Varia tion in case defi ni tion

LCDC Re port TA BLE 1 Na tional no ti fi able dis eases
(7) Bul le tin board sys tem; CCDR Can ada Com mu ni ca ble Dis ease Re port pub lished; the most re cent of these in cluded the pro ceed ings of the ex pert work ing group meet ing on emerg ing in fec tious dis eases, which met at Lac Trem blant(7), and the No ti fi able Dis eases An nual Sum mary for 1993.Other pub lished re ports in clude the quar terly Mea sles Up date and the Quar terly AIDS Up date.Regu lar un pub lished re ports to spe cial in ter est groups in clude a weekly sum mary of na tional and in ter national com mu ni ca ble dis ease is sues and a weekly sur veillance re port on res pi ra tory vi rus in fec tions.