communicable disease surveillance robert allard mdcm msc frcpc october 2004
TRANSCRIPT
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 hypotheses Incomplete data on
population Simpler analysis Rapid dissemination of
results Results not necessarily
generalizable Triggers intervention
Time-limited Tests hypotheses 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
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
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 1998
1 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 disease
9 Diphtheria Hepatitis C
10 Chickenpox Botulism
11 Meningococcal Poliomyelitis
infection
12 Gonococcal Creutzfeld-Jacob Disease
infection
VALIDITY OF REPORTS(False positives)
Surveillance 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)
0
10
20
30
40
50
60
70
80
90
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
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, personor
Who, what, where, when, why (how)? How = by what mode of transmission? Three basic modes:
Person-to-person Common source Vector-borne
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. Or they could be in fact the same cause. A common cause may be easier to
identify (of all exposures, it is the one that cases share)
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
SPATIAL CLUSTERING
Less useful for surveillance in urban compared to rural environments
Very many methods exist Most require more or less unrealistic
assumptions Most promising: SaTScan (see satscan.org)
SaTScan v4.0.3 _____________________________
Program run on: Tue Sep 14 08:39:26 2004
Purely Spatial analysis scanning for clusters with high rates using the Bernoulli model. ________________________________________________________________
SUMMARY OF DATA
Study period .........: 2004/1/4 - 2004/9/11 Number of census areas: 12153 Total population .....: 1996 Total cases ..........: 68 ________________________________________________________________
MOST LIKELY CLUSTER
1.Location IDs included.: 24490070, 24490072, 24490071, 24490075, 24490125, 24490073, 24490074, 24490108, 24490069, 24490078, 24490076 Coordinates / radius..: (45.835072 N, 72.416458 W) / 3.35 km Population............: 3 Number of cases.......: 3 (0.10 expected) Overall relative risk.: 29.353 Log likelihood ratio..: 10.203094 Monte Carlo rank......: 22/1000 P-value...............: 0.022
SECONDARY CLUSTERS
2.Location IDs included.: 24650090, 24650089, 24650095, 24650092, 24650091, 24650103, 24650087, 24650105, 24650104, 24650094, 24650096 Coordinates / radius..: (45.601601 N, 73.716415 W) / 0.75 km Population............: 3 Number of cases.......: 3 (0.10 expected) Overall relative risk.: 29.353 Log likelihood ratio..: 10.203094 Monte Carlo rank......: 22/1000 P-value...............: 0.022
3.Location IDs included.: 24570180, 24590138, 24570179, 24590137, 24590133, 24590129, 24590131, 24570089, 24590128, 24590132, 24590134, 24590130, 24590139, 24590135, 24590119, 24590136, 24590114, 24590115, 24590113 Coordinates / radius..: (45.580250 N, 73.286354 W) / 3.73 km Population............: 3 Number of cases.......: 3 (0.10 expected) Overall relative risk.: 29.353 Log likelihood ratio..: 10.203094 Monte Carlo rank......: 22/1000 P-value...............: 0.022
4.Location IDs included.: 24700011, 24700010, 24700004, 24700003, 24700009, 24700007, 24700002, 24700008, 24700012, 24700058, 24700001, 24700006, 24700005, 24700013, 24700060 Coordinates / radius..: (45.294823 N, 73.843208 W) / 5.58 km Population............: 5 Number of cases.......: 3 (0.17 expected) Overall relative risk.: 17.612 Log likelihood ratio..: 6.904386 Monte Carlo rank......: 263/1000 P-value...............: 0.263
GROWING IMPORTANCEOF ZOONOSES
vCJD, SARS, WNV, avian influenza, 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 (?)
Link to professional organizations Keep it passive Provide feedback and other benefits Surveillance objectives must be
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, vCJD (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 (Clostridium difficile!) 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.
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 synthesized into syndromes if possible Clusters of syndromes are tested for Significant clusters flagged for further investigation
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
Uses of DNA “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
CONCLUSION: research vs surveillance
Collaboration between the research and public health communities is increasing
Research and surveillance methodologies are converging
The objectives of each remain different:is one trying to answer questions of local interest, as rapidly as possible of general interest, as validly as possible