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Communicable disease surveillance

Communicable disease surveillance. Robert Allard MDCM MSc FRCPC October 2003. Infectious disease surveillance designs. Traditional disease notification Outbreak investigation Cluster investigation Enhanced surveillance Sentinel surveillance Emerging infectious diseases

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Communicable disease surveillance

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  1. Communicable disease surveillance Robert Allard MDCM MSc FRCPC October 2003

  2. 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

  3. 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

  4. 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 COMMUNICABLE DISEASESURVEILLANCE or RESEARCH?

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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

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

  12. 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

  13. ANALYSIS OF SURVEILLANCE DATA “Monitoring trends is the cornerstone objective of most surveillance systems.” Buehler, Modern Epidemiology (1998), p. 438

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

  15. MAIN MONTHLY SURVEILLANCEOUTPUT, MONTREAL

  16. Detail of preceding table:

  17. “Figure 1” analysis

  18. ANNUAL FORECASTS

  19. Importance of explainingthe main surveillance results Note explicative concernant les statistiques des maladies infectieuses à déclaration obligatoire (MADO) et autres maladies infectieuses sous surveillance Période 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.

  20. Outbreak investigation • Time, place, personor • 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

  21. 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

  22. 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)

  23. 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.

  24. 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

  25. Box-Jenkins modelling:the time series and the forecasts

  26. SPATIAL CLUSTERING • Less useful for surveillance in urban compared to rural environments • Very many methods exist • Most require more or less unrealistic assumptions

  27. WNV-INFECTED CORVIDS (red)

  28. SMOOTHED MAP OF INFECTED CORVIDS(Thanks to Christian Back)

  29. HUMAN WNV CASES(a few days later, Sept. 19, 2003)

  30. 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

  31. 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?

  32. 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

  33. CHOICE OF SENTINELS • Physicians • Pharmacies • Laboratories • Hospitals • Public health Units, etc. • Combination of sources (see http://www.cdc.gov/foodnet/surveys.htm)

  34. SUCCESS FACTORS (?) • Linked to professional organizations • Passive • Provide feedback and other benefits • Surveillance objectives are • Relevant • Flexible • Suggested by participants

  35. 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

  36. 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

  37. 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

  38. 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 SOME EMERGING AGENTS

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

  40. 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

  41. 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

  42. 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.

  43. Probable Case: • A suspect case with radiographic evidence of infiltrates consistent with pneumoniaor 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.

  44. SARS EPIDEMIC CURVE, CANADA, 2003

  45. 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

  46. 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

  47. 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

  48. Simple temporal analysis of HMO data(Thanks to Richard Platt)

  49. Simple spatial analysis of HMO data(Thanks to Richard Platt)

  50. 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

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