Communicable disease surveillance

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Communicable disease surveillance

• Robert Allard MDCM MSc FRCPC
• November 2 2006

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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

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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

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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

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Traditional disease notification

• Legal framework
• List of reportable (or notifiable) conditions
• Verification and analysis
• Investigation
• Public health intervention
• Dissemination of results
• Evaluation and updating

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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

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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

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• 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

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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

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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

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Stages in the reporting of shigellosis (CDC, ca.
1970)
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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

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ANALYSIS OF SURVEILLANCE DATA

• Monitoring trends is the cornerstone
• objective of most surveillance systems.
• Buehler, in Rothman et al, Modern Epidemiology
  (1998), p. 438

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Standard outputs

• Periodic reports
• Mail and internet
• Monthly
• Commented
• Newsletter
• Special alerts
• fax and e-mail
• Annual report

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MAIN MONTHLY SURVEILLANCEOUTPUT, MONTREAL
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Detail of preceding table
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Outbreak investigation

• Time, place, person or
• Who, what, where, when, why (how)?
• How by what mode of transmission?
• Three basic modes
• Person-to-person
• Common source
• Vector-borne

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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, causedby a different
  strain than caused the outbreak

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Importance of explainingthe main surveillance
results

• Maladies à déclaration obligatoire - Information
  aux professionnels
• Explanatory notes on statistics, period 8 - 2005,
  weeks 29 to 32. 17-07-2005 to 13-08-2005

Cryptosporidiosis Two cases have been reported
since the end of period 8, both in children from
a family who has no history of travel outside
Québec and for whom no risk factors have been
identified. In particular, there is no link with
the outbreak of over 3000 cases attributable to
aquatic exposure at Seneca Lake State Park in New
York State . Since Canadians accounted for some
of the cases, this disease will be monitored more
closely for a certain time. We wish to thank
Jérôme Latreille for the information provided.
Explanatory note prepared by Robert Allard,
MD, MSc., FRCPC - rallard_at_santepub-mtl.qc.ca
Lucie Bédard, Msc. inf., mph -
lbedard_at_santepub-mtl.qc.ca Epidemiological
Surveillance Bureau [phone]
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CLUSTERINGtemporal and spatial

• Cluster
• A geographically bounded group of occurrences
• of sufficient size and concentration
• to be unlikely to have occurred by chance.
  
• (Knox, 1989)

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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.

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TEMPORAL CLUSTERING

• Based on time-series (of numbers of notified
  cases)
• Time unit
• Week
• Month (period)
• Favourite statistical methods
• Figure 1 method
• ARIMA or Box-Jenkins modelling

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Figure 1 analysis
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Box-Jenkins modellingthe time series and the
forecasts
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Box-Jenkins modellingthe time series and the
forecasts
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(No Transcript)
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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)

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Reported dead corvid sightings
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WNV-INFECTED CORVIDS (red)
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SMOOTHED MAPOF SAME INFECTED CORVIDS(Thanks to
Christian Back)
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HUMAN WNV CASES(a few days later, Sept. 19,
2003)
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Spatial clustering by SaTScan

• SaTScan v4.0.3
• _____________________________
• Program run on Tue Sep 14 083926 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
• __________________________________________________
  ______________

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Spatial clustering by SaTScan

• 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

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Clusters, week 30, 2003 Cases
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Clusters, week 30, 2003 Controls
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Clostridium difficile surveillance in
hospitalsSpace-time clustering by SaTScan
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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?

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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

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CHOICE OF SENTINELS

• Physicians
• Pharmacies
• Laboratories
• Hospitals
• Public health Units, etc.
• Combination of sources (see http//www.cdc.gov/f
  oodnet/surveys.htm)

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SUCCESS FACTORS (?)

• Link to professional organizations
• Keep it passive
• Provide feedback and other benefits
• Surveillance objectives must be
• Relevant
• Flexible
• Suggested by participants

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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

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• Results
• European travellers 48Immigrants 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

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EMERGING INFECTIOUS DISEASES (EID)

• 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

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SOME EMERGING AGENTS

• 1973 Rotavirus
• 1977 Ebola virus
• 1977 Legionellosis
• 1981 HIV
• 1982 E.coli O157H7
• 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
• 2004 H5N1

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FACTORS IN EMERGENCE

• Microbial adaptation and change
• Drug resistance
• New virulence or toxin production
• Environmental changes
• Global warming
• Deforestation
• Societal events
• Impoverishment
• War
• Immigration

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• 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

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GROWING IMPORTANCEOF ZOONOSES

• vCJD, SARS, WNV, avian influenza, monkeypox,
  rabies, influenza H5N1, 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

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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 WHOs
• This case definition was crucial to
• Day-to-day surveillance and control activities
• Description of outbreak

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SARS surveillance case definition

• Suspect Case A person presenting with
• Fever (over 38 degrees Celsius)
• AND
• Cough or breathing difficulty
• AND
• 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.

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• 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.

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SARS EPIDEMIC CURVE, CANADA, 2003
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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
• 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

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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

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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

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Syndromic surveillance in NYC, 2001-2

• Diarrheal and fever/flu syndromes
• Satscan space-time analysis
• Shaded areas residence-based signals
• Circles hospital-based signals
• The largest hospital signal immediately
  preceded a citywide increase in diarrheal
  activity that lasted approximately 6 wks
• The other signals were concurrent with the
  beginning of outbreaks of the same disease

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Syndromic surveillance in NYC, 2001-2Diarrheal
syndromes
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Syndromic surveillance in Montreal

• Detect in real time any major infectious or
  environmental threat to public health
• Data provided daily by the Agency and
  Urgences-Santé
• Times series of
• Ambulance transports
• ER admissions (by hospital)
• Hospital admissions (by hospital)
• Total
• From ER
• Deaths in and out of hospital etc.
• Daily space-time analysis by SaTScan
• Much less specific than true syndromic
  surveillance

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Syndromic surveillance in MontrealRecent signals
(plt0.0027)
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MOLECULAR BIOLOGYAND SURVEILLANCE

• Based on ability to distinguish between different
  genotypes of the same agent
• Different methods, short of complete 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

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DNA electrophoretic pattern
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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

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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

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• 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

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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 differentis one
  trying to answer questions
• of local interest, as rapidly as possible
• of general interest, as validly as possible