Post on 25-Feb-2016
description
Communicable disease surveillance
Robert Allard MDCM MSc FRCPC
October 2003
Infectious diseasesurveillance designs
Traditional disease notification Outbreak investigation Cluster investigation Enhanced surveillance Sentinel surveillance Emerging infectious diseases
diagnosis-based surveillance syndromic surveillance
Molecular biology and surveillance
Definition“Surveillance, when applied to a disease, means the continued watchfulness over the distribution and trends
of incidence through the systematic collection, consolidation and
evaluation of morbidity and mortality reports and other relevant data.
Intrinsic in the concept is the regular dissemination of the basic data and interpretation to all who have contributed and to all others who need to know.
The concept, however, does not encompass direct responsibility for control activities.”
A.D. Langmuir, 1963
COMMUNICABLE DISEASESURVEILLANCE or RESEARCH? Ongoing Generates hypothesis Incomplete data on
population Simpler analysis Rapid dissemination of
results Results not necessarily
generalizable Triggers intervention
Time-limited Tests hypothesis Complete data on sample
More complex analysis Slower dissemination of
results Aims at generalizability
Looser link to intervention
Traditional disease notification Legal framework List of reportable (or notifiable) conditions Verification and analysis Investigation Public health intervention Dissemination of results Evaluation and updating
DISEASE SELECTION CRITERIA Incidence Morbidity Mortality / severity / lethality Communicability / potential for outbreaks Preventability Changing pattern in previous 5 years Socioeconomic burden Public health response necessary Public perception of risk International and other sector consideration
Rank (Priority for Canadian government, first 12 of 43) 1988 19981 Measles HIV 2 Tuberculosis AIDS 3 AIDS Laboratory confirmed influenza 4 Hepatitis B Tuberculosis 5 Pertussis Measles 6 Salmonellosis Rabies 7 Rubella Pertussis 8 H. influenzae Invasive meningococcal disease invasive disease9 Diphtheria Hepatitis C 10 Chickenpox Botulism 11 Meningococcal Poliomyelitis infection 12 Gonococcal Creutzfeld-Jacob Disease infection
Legal framework Required for
transmission of confidential information investigation intervention
Varies between jurisdictions Québec specifics:
no more anonymously reportable conditions HIV-AIDS is “provincially reportable” duty to “signal” non-reportable conditions distinction between “surveillance” and “vigie” surveillance ethics committee
VALIDITY OF REPORTS(False positives) Nosologic definitions
May be different from clinical definitions Laboratory confirmation The problem of nearly eliminated diseases
Most positives are false positives• Poor clinical diagnostic accuracy• Importance of eliminating alternate Dx
Only confirmed cases enter statistics
COMPLETENESS OF REPORTING(False negatives) Varies by
Type of reporting (active, passive) Source of reports Disease
Need not be high, provided it is stable More important if intervention is possible
Stages in the reporting of shigellosis (CDC, ca. 1970)
0102030405060708090
100
Inf Symp Cons Cult Pos Report Inv Neg
ROUTINE INVESTIGATIONOF REPORTED CASES MD, patient and/or relative are interviewed Not all cases can be investigated
Intervention possible Transmissibility is high Case is unusual Outbreak is suspected
ANALYSIS OF SURVEILLANCE DATA
“Monitoring trends is the cornerstone objective of most surveillance systems.”
Buehler, Modern Epidemiology (1998), p. 438
Standard outputs Periodic reports
Mail and internet Monthly Commented
Newsletter Special alerts
fax and e-mail Annual report
MAIN MONTHLY SURVEILLANCEOUTPUT, MONTREAL 2003 au 12 juil. 2002 au 13 juil. 2001 au 14 juil.
Courant Cumulatif Courant Cumulatif Courant Cumulatif
Maladie N Taux N Taux N Taux N Taux N Taux N Taux
Amibiase 11 7.8 76 7.7 9 6.4 63 6.4 8 5.7 77 7.9
Botulisme 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0
Brucellose 0 0.0 1 0.1 0 0.0 0 0.0 0 0.0 1 0.1
Campylobactériose 27 19.2 181 18.3 52 37.0 224 22.8 37 26.5 184 18.8
Chancre mou 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 0.1
Infection à Chlamydia trachomatis 182 129.1 1706 172.9 201 143.2 1697 172.7 195 139.5 1598 163.3
Choléra 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0
Coqueluche 3 2.1 17 1.7 6 4.3 65 6.6 7 5.0 74 7.6
Diarrhée épidémique 0 0.0 27 2.7 1 0.7 4 0.4 0 0.0 5 0.5
Encéphalite transmise par arthropodes 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0
Entérite à E. coli O157:H7 0 0.0 4 0.4 2 1.4 19 1.9 9 6.4 27 2.8
Entérite à Yersinia enterocolitica 2 1.4 16 1.6 5 3.6 13 1.3 2 1.4 20 2.0
Fièvre paratyphoïde 0 0.0 3 0.3 1 0.7 2 0.2 0 0.0 4 0.4
Fièvre typhoïde 1 0.7 5 0.5 0 0.0 8 0.8 1 0.7 4 0.4
Fièvre Q 0 0.0 0 0.0 0 0.0 1 0.1 0 0.0 0 0.0
Giardiase 16 11.4 153 15.5 19 13.5 117 11.9 18 12.9 135 13.8
Detail of preceding table:
“Figure 1” analysis
ANNUAL FORECASTS
Importance of explainingthe main surveillance resultsNote explicative concernant les statistiques des maladies infectieuses à déclaration
obligatoire (MADO) et autres maladies infectieuses sous surveillancePériode 08 de l’année 2003 (semaines 29 à 32 13-07-2003 au 09-08-2003])
Shigellose
L’excès significatif de cas de shigellose s’explique par une éclosion parmi le personnel d’un établissement de soins de Montréal. Quinze cas ont été identifiés, dont treize confirmés par culture (S. sonnei) et deux reliés épidémiologiquement à un cas confirmé. Les symptômes ont commencé entre le 14 et le 18 juillet. De plus, quelques cas ont été déclarés dans la communauté, dus au même agent, et apparemment reliés à un ou des restaurants. Les organismes impliqués dans l’enquête (DSP, CUVM, MAPAQ) ont exploré divers liens possibles entre tous ces cas. L’éclosion est maintenant considérée comme terminée et des aliments achetés à la cafétéria semblent être la source commune de l’infection pour les cas dans l’établissement.Remerciements à Mme Hélène Rodrigue pour l’information.
Outbreak investigation Time, place, person
or Who, what, where, when, why?
or rather Who, what, where, when, how? How = by what mode of transmission? Two basic modes:
Person-to-person Common source
DESIGNS FOROUTBREAK INVESTIGATIONS Descriptive
Common exposure • Suitable when exposure is very specific
Person to person contacts Case-control
Controls are:• Other attendees at event who remained healthy• Population sample (often drawn by RDD)
Case-case Controls are:
• Cases of other reportable diseases• Cases of the same disease, caused
by a different strain than caused the outbreak
CLUSTERING:temporal and spatial
Cluster:
“A geographically bounded group of occurrences of sufficient size and concentration to be unlikely to have occurred by chance.”
(Knox, 1989)
WHY THE INTERESTIN CLUSTERING? Cases are effects. If effects are clustered, their causes could
also be. Causes with the same effects may be one
and the same. A common cause may be easier to
identify (how ?) remove or control.
TEMPORAL CLUSTERING Based on time-series (of numbers of notified cases) Time unit:
Week Month (period)
Favourite statistical methods: ARIMA or Box-Jenkins modelling “Figure 1” method
Box-Jenkins modelling:the time series and the forecasts
SPATIAL CLUSTERING Less useful for surveillance in urban
compared to rural environments Very many methods exist Most require more or less unrealistic
assumptions
WNV-INFECTED CORVIDS (red)
SMOOTHED MAP OF INFECTED CORVIDS(Thanks to Christian Back)
HUMAN WNV CASES(a few days later, Sept. 19, 2003)
GROWING IMPORTANCEOF ZOONOSES vCJD, SARS, WNV, monkeypox, rabies etc. Disease trends in other species have to be
followed and related to trends in humans Interdisciplinary collaboration essential Worrisome development,
but very stimulating work
ENHANCED SURVEILLANCE Priority problem identified Concept is elastic: traditional surveillance plus any
combination of Extra resources allocated Increased collaboration between government levels Standardized data collection Increased data quality control Access to better laboratory tests Increased analytic possibilities Other surveillance methods
Greater potential to guide policy making?
SENTINEL SURVEILLANCE Does not seek completeness Uses purposely selected sources of information Prefers sources likely to observe earliest occurrence
of phenomenon under surveillance May be active or passive Relies heavily on real-time communication Positive findings often trigger other forms of
surveillance
CHOICE OF SENTINELS Physicians Pharmacies Laboratories Hospitals Public health Units, etc. Combination of sources
(see http://www.cdc.gov/foodnet/surveys.htm)
SUCCESS FACTORS (?) Linked to professional organizations Passive Provide feedback and other benefits Surveillance objectives are
Relevant Flexible Suggested by participants
IMPORTED FALCIPARUM MALARIA IN EUROPE European Network on Surveillance of
Imported Infectious Diseases About 45 hospital departments of infectious
diseases 1659 patients seen in 1999-2000 About 10% of all patients with malaria seen in
Europe
Results: European travellers 48%
Immigrants 52% Country of infection: West Africa for 63% Chemoprophylaxis had been taken by
• 40% of travellers• 28% of immigrants
Lethality: 5 patients (all travellers) Useful results, but is it surveillance?
Continuous collection, analysis, reporting? No denominators or analysis of trends
EMERGINGINFECTIOUS DISEASES
Strategic/political aspects of the concept “Emerging infections are those diseases whose
incidence has increased within the past two decades or … threatens to increase in the near future.” (NY ACAD SCI)
An emerging infection can be due to an agent previously unknown previously unknown in humans previously unknown in a given area previously non pathogenic or less pathogenic previously non resistant to antibiotics previously controlled by preventive measures
SOME EMERGING AGENTS 1973 Rotavirus 1977 Ebola virus 1977 Legionellosis 1981 HIV 1982 E.coli O157:H7 1982 Lyme disease 1983 H. pylori
1986 BSE, CJD (prions) 1989 Hepatitis C 1992 Cholera O139 1995 HHV-8 1999 WNV 2001 Anthrax 2002 SARS CoV
FACTORS IN EMERGENCE Microbial adaptation and change
Drug resistance New virulence or toxin production
Environmental changes Global warming Deforestation
Societal events Impoverishment War Immigration
Human behaviour Sexual, drug use Travel Use of child care facilities
Food production Globalization
Health care Widespread use of antibiotics Immunosuppressive drugs
Public health infrastructure Curtailment of preventive programs
EID: diagnosis-based surveillance SARS: severe acute respiratory syndrome Originated in SE Asia in November 2002 Single agent suspected early (SARS CoV) Importation to Toronto (“superspreader”) Canada-wide alert in April 2003 Canadian case definition based on WHO’s This case definition was crucial to
Day-to-day surveillance and control activities Description of outbreak
Surveillance case definition: Suspect Case: A person presenting with:
Fever (over 38 degrees Celsius)AND Cough or breathing difficultyAND One or more of the following exposures during the 10 days prior to
the onset of symptoms:• Close contact with a person who is a suspect or probable case• Recent travel to an "Area with recent local transmission" of SARS
outside of Canada• Recent travel or visit to an identified setting in Canada where exposure
to SARS may have occurred (e.g., hospital [including any hospital with an occupied SARS unit], household, workplace, school, etc.). This includes inpatients, employees or visitors to an institution if the exposure setting is an institution.
Probable Case: A suspect case with radiographic evidence of infiltrates
consistent with pneumonia or respiratory distress syndrome (RDS) on chest x-ray (CXR).
OR A suspect case with autopsy findings consistent with the
pathology of RDS without an identifiable cause.
Exclusion Criteria A suspect or probable case should be excluded if an
alternate diagnosis can fully explain their illness.
SARS EPIDEMIC CURVE, CANADA, 2003
EID: syndromic surveillance Observes the occurrence not of diagnosed
disease but of a pre-defined syndrome Syndrome = “a pattern of symptoms
indicative of some disease”, usually unidentified
The syndrome may be associated with one or more disease entities
A diagnosis is sought (for surveillance) only when a cluster of the syndrome is detected
EXAMPLES OF SYNDROMES FOR SURVEILLANCE Fever + upper or lower respiratory signs or
symptoms (plague,anthrax, ricin, staph. toxin or …)
Fever + rash (smallpox or …)
Fever + hemorrhages (Ebola, Marburg or …)
Fever + GI symptoms (salmonellosis or …)
Cranial-nerve impairment (botulism or …)
Fever + unexplained death
OPERATIONALIZATION OF SYNDROMIC SURVEILLANCE Most promising general source of information:
emergency department (or other primary care source) presenting complaints (PC)
Information is computerized on site transmitted periodically to central server scanned to extract PCs and other information
PCs are syntesized onto syndromes if possible Clusters of syndromes are tested for Significant clusters flagged for further investigation
Simple temporal analysis of HMO data(Thanks to Richard Platt)
Simple spatial analysis of HMO data(Thanks to Richard Platt)
MOLECULAR BIOLOGYAND SURVEILLANCE
Based on ability to distinguish different strains of same agent, based on its nucleic acid (genotype)
Different methods, short of sequencing, can be used
Must be able to detect mutations that are Frequent enough to have produced many
different strains over the years Rare enough not to occur during an outbreak
DNA electrophoretic pattern
Uses of fingerprinting Prove that cases in an outbreak are related Prove that suspected vehicle is the true common
source Identify outbreaks missed by traditional methods
TB in chronic care hospitals for old people Help select cases and controls in a case-case study
Cases: cases caused by the outbreak strain Controls: cases caused by non outbreak strains Goal: identify mode(s) of transmission specific to this
outbreak
Example of case-case study Listeriosis outbreak (meningitis, sepsis, especially in
pregnant women) in France Positive L. monocytogenes culture from normally
sterile site between 99/11/12 and 00/02/28 Cases: 29 strain-associated cases
Excluded were:• 2 deaths• 1 case whose status (as case) was known before interview
Controls: 32 non strain-associated cases
Results: Adjusted ORs and 95% CI
• Jellied pork tongue: 75.5 (4.7 - 1216)• Pâté de campagne: 8.9 (1.7 - 46.1)• Cooked ham: 7.1 (0.7 - 71.8)
All cases had eaten at least one of the above Recommendation against eating the pork tongue
made on Feb. 22, 2000 Outbreak strain in foodstuffs
Identified in some (rillettes: OR = 1.1 [0.3 – 3.8]) Not identified in jellied pork tongue
• No recall, as specific brand could not be incriminated
CONCLUSIONLevel Main surveillance challenge Local: best use of scarce resources
Provincial: adequate response to non-local outbreaks
National: uniformization of standards while respecting provincial autonomy
International: uniformization of quality of data in the face of wide economic and cultural disparities
Selecting the most appropriate design is relevant at every level.