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Surveillance in Public Health Dimension

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  1. 1. Surveillance Dr Janvi Chaubey B.D.S. & PGD in Public Health
  2. 2. Surveillance  "sur" means "from above" and "veiller" means "to watch  Surveillance is a systematic process of collection, transmission, analysis and feedback of public health data for decision making.
  3. 3. • It serves as an early warning system for impending public health emergencies. • It document the impact of an intervention, or track progress towards specified goals • Monitor and clarify the epidemiology of health problems, to allow priorities to be set and to inform public health policy and strategies. http://www.who.int/topics/public_health_surveillance/en
  4. 4. 4 A dynamic vision of surveillance Collect and transmit data Analyze data Feedback information Make decisions All levels use information to make decisions Collect and transmit data Analyze data Feedback information Make decisions All levels use information to make decisions
  5. 5. Steps in establishing and maintaining surveillance system Establish Goals Develop Case definitions Select appropriate personnel Acquire tools and clearances for collection , analysis and dissemination Implement surveillance system Evaluate surveillance activities
  6. 6. Purpose of Surveillance 1. Establish the baseline of a health condition 2. Understand trends and pattern of disease 3. Detect outbreaks or emergence of new disease 4. Estimate the magnitude of health problem 5. Identify resources needed during and after public health emergencies 6. Evaluate public health programs and control measures 7. Determine nature and history of disease 8. Monitor changes in infectious agents 9. Set research priorities 10. Stimulate research 11. Inform research plan and implementation 12. Support public health program planning 13. Monitor changes in public health practice Source: Adopted from Thacker sb,Berkelman RI. Public health Surveillance1998
  7. 7. Source: http://www.uic.edu/sph/prepare/courses/ph490/resources/epilesson.pdf
  8. 8. WHO’s standard protocol for Surveillance: • Is the case definition clear? appropriate? consistent throughout the surveillance system? • Is the reporting mechanism clear? Efficient? of appropriate reporting periodicity? available to all relevant persons and institutions? • Is the analysis of data appropriate? susceptible to proper presentation? used for decision- making? • Do the personnel involved have a good understanding of the value of the surveillance system? Source: WHO Recommended Surveillance Standards WHO/CDS/CSR/ISR/99.2
  9. 9. Analysis of Surveillance Data A. Time • Graph over time B. Place • Map C. Person • Breakdown by age, sex or personal characteristics, vaccination status
  10. 10. Numerator issues: • Definition • Ascertainment • Severity Denominator issues: • Population base • Which denominator
  11. 11. Types of Surveillance: (a) A focused location for surveillance (such as health facility-based surveillance or community based surveillance). (b) A designated or representative health facility or reporting site for early warning of epidemic or pandemic events (sentinel surveillance). (c) Surveillance conducted at laboratories for detecting events or trends not necessarily evident at other sites. (d) Disease-specific surveillance involving activities aimed at targeted health data for a specific disease. (Disease surveillance and notifiable disease reporting system) WHO integrated disease surveillance and response in the African region a guide for establishing community based surveillance Population based
  12. 12. Types of surveillance Surveillance Hospital based Surveillance Community based Surveillance Active/ Passive
  13. 13. Community based surveillance: • Community-based Surveillance (CBS) is an active process of community participation in detecting, reporting, responding to and monitoring health events in the community. • The main reporters are community members who detect and report cases that might be otherwise not be reported to health care facilities • To do this , community awareness campaign is essential to carry out like educating them about the signs and symptom of disease.
  14. 14. • Low and middle income countries often uses CBS to track diseases • It is conducted by volunteers who receive training on health conditions from health care worker or health care facilities to detect and report suspected cases to the facility • The scope of CBS is limited to systematic on- going collection of data on events and diseases using simplified case definitions and forms and reporting to health facilities
  15. 15. How to establish community based surveillance in its catchment area? (a) Mapping the catchment area and determining the number of CBS focal points needed. (b) Identifying community representatives willing to be CBS focal points and accepted by the community to play such a role. (c) Training the focal points regarding the use of case definitions and actions, and timelines for reporting intervals. (d) Defines a mechanism for regular feedback and support to the CBS.
  16. 16. CBS should be a routine function for: (a) Pre-epidemic period (to provide early warning or alerts) (b) Period during epidemic (to actively detect and respond to cases and deaths) (c) Post-epidemic period (to monitor progress with disease control activities) Integrated disease surveillance and response in the african region ; A guide for establishing community based surveillance
  17. 17. Advantages: • To facilitate easy and early reporting, to keep vigilance at the community level • To get the community involved so they understand their health problems. • To help people to be free from diseases • To improve the health of the people • Detecting individuals who do not seek medical care • Building health care network within community
  18. 18. Disadvantages • Sensitivity and specificity of case detection • Positive predictive value of the trigger events • Timeliness of reporting and • Acceptability of the system, based on interviews of key informants in a sample of villages. • All Health conditions are not suitable for CBS For eg STDs because of their associated social pressure and consequences
  19. 19. Hospital based surveillance • The main reporter in this surveillance system is physician or any proper system placed in hospital for regularly reporting and capturing information. • The hospital may assign any physician or proper system to take responsibility for such reporting • This type of surveillance requires an accurate estimation of the demographic characteristics of the population under surveillance • The hospital administration should be fully informed and understand the importance of surveillance.
  20. 20. Selection of surveillance population and participating hospitals • It should be demographically and geographically well defined, and data should be available on e.g. age distribution and numbers of births and deaths • The numbers of children in specific age groups • Surveillance is best initiated in a population that has been stable and is expected to best able during the period of surveillance.
  21. 21. • A population that uses a single hospital or a small number of hospitals and has good access to it or them would be ideal. A study is easiest to conduct if a single large hospital serves the population and if the services it provides are free. • It is advisable to be aware of the sources of health care in the population under surveillance and the numbers of patients they care for. • Actual size of a surveillance population that would yield accurate estimates is difficult to determine, given the paucity of data on hospitalizations in developing countries and the unknown sensitivity of each system in detecting and testing cases of gastroenteritis.
  22. 22. Advantages: • Hospitalizations are easy to detect and they have good source of well structured data • Hospitalizations represent a significant cost in health resources. • Hospitals are likely to have a laboratory capability
  23. 23. Disadvantages: • Health conditions of mild illness as individual does not seek health care or require hospitalizations • Some conditions which are not tracked well in hospitals. (eg MI lead hospitalization could give false estimate of true incidence) • Lack of Representativeness of Reported Cases • Lack of Timeliness • Inconsistency of Case Definitions • To get the denominator i.e. population at risk for calculating the incidence
  24. 24. The final design of surveillance ought to differ based on the context and challenges existing locally, therefore requiring customizable and adaptable strategies to ensure the feasibility of caring out surveillance.
  25. 25. Surveillance methodology
  26. 26. Active Surveillance • Active surveillance (“hot pursuit”)identifies cases through screening of hospital admission records, emergency department logs, medical wards, and intensive care units and out-of-hospital facilities, including nursing homes, radiology centers, and physicians’ offices. • Screening is the essential step in active surveillance • Appropriate screening terms and rigorous standardized procedures are necessary to minimize the number of missing cases. Source: Comparison of Active and Passive surveillance for CerebrovascularThe Brain Attack Surveillance in Corpus Christi (BASIC) Project
  27. 27. • The system does not wait for: Case-patients to come to health care facilities Health care facilities to report cases • Health care workers actively reach out to detect cases • Surveillance comes in addition to routine health care delivery. • This method requires more resources than passive surveillance, but is especially useful when it is important to identify all cases
  28. 28. When to consider active surveillance? Informed decision based on vaccine characteristics, pre-licensure data, safety profile of similar vaccine/s, safety signal, other • IS and rotavirus vaccines • Limited pre-registration data • Variation in vaccine characteristics –annual changes to seasonal influenza vaccine • To address vaccine safety ‘concerns’ that may/have damaged confidence • Active surveillance will include cohort and clinical trails.
  29. 29. Advantages • Can be very sensitive • Can collect more detailed information • May be more representative. Disadvantages • High Cost • Labor intensive • Difficult to sustain over time.
  30. 30. Methodology: • It was double blind placebo controlled , Randomized clinical trail to evaluate the efficacy of three doses of Rotavac against severe gastroenteritis which was conducted at three sites (Delhi , Pune and Vellore) in India between 2010 & 2013 Subject recruitment and follow up: Subjects enrolled 6-7 weeks of age Active Surveillance for IS in a phase 3 efficacy trail of a oral monovalent rotavirus vaccines in India - Jacob John
  31. 31. •The phase 3 clinical trail enrolled 6799 children across three sites ( Delhi -3799, Pune -1500, Vellore- 1500)  Vaccine(Rotavac) Arm -4419  Placebo Arm-2191
  32. 32. • Randomized in 2:1 ratio to receive 3 doses of vaccine or a placebo. • The first 1/3rd of the participants enrolled in the study at all three sites were followed for their safety (staff doing daily contacts for 14 days as follow up for vaccine) • 2/3rd included in the trail were followed weekly until the age of two years of follow up. • Caregivers were given mobile phones and access to the study team whenever the child suffered from the symptoms of acute gastroenteritis.
  33. 33. Screening and management of suspected IS: •Screening criteria for suspected IS were identified and treated appropriately •Each children with IS were identified and examined by the study team and was taken for pediatric consultation and hospitalization if required •All diagnosis was confirmed through Ultrasound screening
  34. 34. Adjunction of Cases: •Independent Case adjunction committee blinded to the children allocation to different groups reviewed all clinical reports and radiologic evidence of IS cases and brightons criteria of IS •This committee constitutes senior pediatric surgeon , pediatric radiologist and pediatrician. •Relative risk was calculated for 7 day ,14 day and 60 day periods after any dose and 365 day period after first dose.
  35. 35. John et al,2014
  36. 36. Results:  The incidence rate of confirmed IS among vaccine group was 94/100,000 child years (95% CI ,41,185) and 71/100,000 child years years (95% CI ,15,206) in Placebo group. No temporal association with vaccination (including 2 year of follow up, the difference between the treatment arm was not statistically significant OR ratio calculated 1.34
  37. 37. Limitations: • Due to usage of broad criteria for identifying cases in active surveillance resulted in screening of children with non specific illness were also have undergone ultrasound screening • This surveillance has also diagnosed large of transient cases .
  38. 38. Passive Surveillance • Passive surveillance(or “cold pursuit” )ascertains cases by searching hospital discharge diagnoses. • Health care facilities or providers report cases as they present in health care facilities • No specific efforts are made to make sure all cases are reported • Surveillance is integrated to routine health care delivery • Cases are identified as per case definition
  39. 39. Strengths • Large population cover • Simple to operate/inexpensive • Signal detection • Hypothesis generation • Triggers further investigation • Cost • Easier to design and carry out • Useful for monitoring trends over time
  40. 40. Weaknesses • Reporting biases –Under-reporting • Stimulated reporting • Inconsistent data quality/completeness • Can’t determine AEFI incidence • Not designed to assess causality • Low sensitivity • Amount of data available is limited • May not be representative
  41. 41. Methodology: Retrospectively the medical record of confirmed cases of IS in children under age of five , treated during 2007-2012 at two tertiary care hospitals(KMC and CSM Medical university) 1. Study area and participating hospital: were finalized for the surveillance site Retrospective surveillance for IS in children aged less than five years at two tertiary care centers in India - -J.V. Singh
  42. 42. 2. Case definition and data sources: • Screening criteria to identify cases were determined for five complete years . • Inclusion criteria: Child<60 months of age with confirmed diagnosis of IS, using the case definition of Brighton collaboration 3. Data collection and analysis: • The data was pooled and analyzed according to age , sex, clinical signs, year and month of hospitalization ,diagnostics and treatment related characteristics
  43. 43. • The most common diagnostic methods used were Ultrasonography and abdominal radiography with most cases being treated surgically (71%). The median length of hospital stay was 8 days (range 1-40) and mean was 10.2 days. Records of any fatality due to intussusception were not found during the review of the records.
  44. 44. Results: • Over a five to six year observation period 187 confirmed cases of intussusception , were identified , of which 75% were males. The median age of intussusception was 8 months, and most of the cases presented were below 12 months • A possible trend in the distribution of cases with the highest number of cases being reported in the month of April and lowest in the month of October.
  45. 45. Limitations • Lack of complete data on immunization • Inability to define the catchment area • Tertiary care referral centers were selected ,so might be most severe cases were covered.
  46. 46. Stimulated passive surveillance • Health care facilities or providers report cases as they present in health care facilities • Special efforts made to maximize reporting through reminders, visits • Surveillance remains integrated to routine health care delivery
  47. 47. Methodology: •Surveillance of IS presenting in first year of life , within the period of 1st March 2008 & 31st March 2009 •BPSU was used in collaboration with BAPS • Criteria for screening was established which included: Infants admitted with suspected or confirmed cases of IS during the study period in NHS and equivalent hospitals across UK and republic of Ireland. Prospective Surveillance study of the management of IS in UK and Irish infants - Lamiya Samad
  48. 48. Cases were classified according to Brighton's collaboration criteria as Definite (level1), Probable (level 2) or Possible (level 3). • BPSU cards were sent to pediatric surgeons and pediatricians to notify the cases of IS meeting the case definition criteria • Clinicians were then contacted with brief study questionnaire on the epidemiology and clinical features of IS • Study response rate was calculated • Duplication of cases identified
  49. 49. • Cases were then classified according to internationally agreed and validated BCC • Incidence rate was calculates using number of definite cases as numerator and total number of live birth ( from the office of national health statistics by linking birth and death by using NHS numbers in the cohort of babies born in 2008 )
  50. 50. Results: 250 Definite cases( excludes readmissions & 4 overseas cases) 110 Duplicates 15 Non responders 12 Probable cases 260 Definite cases 4 Possible cases 401 Cases Notifications
  51. 51. • The base line rate of incidence of intussusception prior to the introduction of rotavirus vaccine into UK vaccine schedule was calculated. • Baseline rates obtained for UK 24.8/100,000 & Republic of Ireland 24.2/100,000
  52. 52. Limitations • Only definite cases of intussusception was included so may cause underreporting so there may be underestimation of actual cases of IS • It rely lot on clinical interest and involvement so consistency and adherence to the study protocol and validation is important
  53. 53. Active & Passive surveillance (Integrated surveillance) • A combination of active and passive systems using a single infrastructure that gathers information about multiple diseases or behaviors of interest to several intervention programs. • It require coordination and collaboration among various programs, first line providers (veterinarians or clinicians), epidemiologists, information system specialists and laboratory personnel, design efforts must consider each of these groups’ needs, capabilities, limitations, logistical assets, budgetary realities and legal requirements.
  54. 54. • In this study surveillance sites were identified then retrospective view of all children was taken. Hospital records of children 0-2 years of age with intussusception treated between Jan 2010 to 31st Aug 2014 were undertaken at CMC Vellore .This hospital caters to 1.9 million outpatient and 120,000 inpatient annually • 61 cases cases of intussusception in children under two year were presented in hospital Intussusception in southern India: Comparison of retrospective analysis and retrospective surveillance -Susan Jahangir
  55. 55. • Retrospective study Cases were identified in two steps:  Ist step : Possible cases of IS were identified through electronic search of the radiology database and operation registers.  2nd step: the diagnosis of IS is then confirmed by reviewing medical records , operation notes and other investigations • The study demonstrates IS identified through active surveillance and those retrospective surveillance differ in presentation , severity of illness, need for intervention and outcome.
  56. 56. • Active surveillance in a vaccine trail was done (N=1500) they were randomized in 2:1 • 16 cases of ultrasound diagnosed IS were identified through active surveillance of cohort of 1500 children participating in rotavirus phase three trail. • In active surveillance all participants were given mobile phones and access to call centre around the clock for the duration of follow up. Any child having the history of symptoms of IS were contacted to minimize the risk of developing IS . • Suspected case was reviewed by pediatrician and those having even transient IS were reviewed by pediatric surgeon
  57. 57. Results IS presenting through routine care identified on retrospective analysis (Passive surveillance) • 61 cases were identified • The median time of onset and arrival to hospital was 48h. • The median age at presentation was 214 days with 52 events occurring in first peak of life IS identified through active surveillance and referral of a vaccine trail cohort (Active surveillance) • 16 cases of IS were diagnosed out of which 7 meet the level 1 criteria • 6 met the level 2 criteria • 3 met the level 3 diagnostic criteria • 8 cases of IS Occurred in first year of life • 16/444 positive ultra sonograms
  58. 58. Limitations • As the data collected were from referral hospitals: So the cases covered were the most serious cases and therefore generalizability issues exists. • Inability to define the catchment area for IS: cases or to have the birth cohort data for the catchment population under study • Lack of complete immunization data: It was difficult to identify the exact number and type of immunization administered prior to hospitalization for IS
  59. 59. Sentinel Surveillance Choose key “location” to monitor for condition of interest. “Locations” might include • Sites • Events • Providers • Animals/Vectors • Choose a “location” that is most susceptible to change.
  60. 60. The following criteria should be considered in selecting a sentinel health facility (usually a general or infectious disease hospital) : • It should be willing to participate. • It serves a relatively large population that has easy access to it. • It has medical staff sufficiently specialized to diagnose, treat and report cases of the disease under surveillance. • It has a high-quality diagnostic laboratory. Source:http://www.who.int/immunization/monitoring_surveillance/burden/vpd/surveillance_type/sentin el/en
  61. 61. • Sentinel surveillance system is used when high- quality data are needed about a particular disease that cannot be obtained through a passive system. • Selected reporting units, with a high probability of seeing cases of the disease in question, good laboratory facilities and experienced well- qualified staff, identify and notify on certain diseases. • Whereas most passive surveillance systems receive data from as many health workers or health facilities as possible, a sentinel system deliberately involves only a limited network of carefully selected reporting sites.
  62. 62. • For example, a network of large hospitals might be used to collect high-quality data on various diseases and their causative organisms, such as invasive bacterial disease caused by Haemophilus influenzae type b, meningococcus or pneumococcus • The success of this approach lies in execution of a system-wide design process that fosters communication and collaboration amongst the multiple stakeholders operating within a surveillance system, two elements that are pivotal for building effective and agile coordinated national response to local and international public health emergencies.
  63. 63. Disadvantage: • If the site is not selected properly, data may not be representative of general population , thereby proving inadequate estimates of incidence and prevalence.
  64. 64. Incidence of intussusceptions in Singaporean children aged less than 2 years: a hospital based prospective study -Kong Boo Phua • This was prospective, hospital-based, multi-centre surveillance study was conducted in hospital • All children aged < 2 years and admitted to the study hospitals with a diagnosis of IS–categorized as definite (ascertained by: radiograph, surgery or by post-mortem examination), probable, possible or suspected cases based on the criteria developed by the Brighton Collaboration Working Group were enrolled. • Data on IS were obtained from the daily admission logs, computerized hospital admission records, emergency department records, surgical records and radiology logs etc
  65. 65. • All departments that were responsible for the management of IS cases were advised to contact the study personnel for each case of IS to ensure that all cases were captured • Annual Incidence of IS = Number of new IS cases reported in a specific year*100,000 The total number of children living in Singapore during the specific year
  66. 66. Results: • Of the 178 children assessed, 167 children with definite IS cases were considered for final analyses; 11 were excluded (six diagnosed as probable IS and four diagnosed as suspected IS; one child’s parents withdrew consent). • The overall incidence of IS was 28.9 (95% CI: 23.0–34.8) and 26.1 (95% CI: 22.2–30.0) per 100,000 child-year in children < 1 year and < 2 years of age, respectively. The majority of IS cases (20 [12.0%]) were reported in children aged 6 months.
  67. 67. Study Design chosen for surveillance
  68. 68. Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future Study begins here Time
  69. 69. Retrospective Study - “to look back”, looks back in time to study events that have already occurred Time Study begins here
  70. 70. 1. Cohort Design: • A cohort is any group of people who are linked in some way and followed over time. • This group is then compared to a similar group that hasn't been exposed to the variable. • Researchers observe what happens to one group that's been exposed to a particular variable — for example, Infants who were vaccinated or non vaccinated whether they develop the disease outcome.
  71. 71. • Follows two or more similar groups that differ with respect to whether they received a vaccine (the “exposure”) to determine how/whether the vaccination affects rates of one or more AEs (the “outcome”)
  72. 72. Source: centre for disease control; Vaccine for children program Cohort Study Design
  73. 73. time Study begins here Study population free of disease Factor present Factor absent disease no disease disease no disease present future
  74. 74. Strengths: • Exposure status determined before disease detection • Subjects selected before disease detection • Can study several outcomes for each exposure Limitations: • Expensive and time-consuming • Inefficient for rare diseases or diseases with long latency • Loss to follow-up
  75. 75. 2. Self controlled case series design: • Simple method that uses data on case patients alone (i.e. without external Control group) • To assess safety or risk exists in defined time intervals after vaccinations. • SCCS method compares the Relative incidence of IS within the risk window of interest with the incidence of risk outside the window of interest. • Robust and cost efficient approach and can be applied in resource poor settings or baseline disease surveillance before vaccine introduction
  76. 76. The major features of SCCS are that (1) it automatically controls for time-fixed covariates that don’t vary within a person during the study period, and (2) only cases (individuals with at least one event) need to be included in the analysis. • It includes only individuals who experienced the AE. Each individual serves as his or her own control. The analysis inherently controls for covariates that remain stable during the study period—for example, race and sex. • SCCSs compare outcome event rates both post vaccination and prevaccination to calculate the relative incidence of AEs
  77. 77. Self control case series study Design 2 3 4 5 6 7 8 Vaccination “Risk” Window Period outside the risk window(“Control”)
  78. 78. • Potential time fixed confounders are of lesser concern in contrast to traditional case control method as only case data is being used. • The self-controlled case series (SCCS) represents one particular methodology that may be useful for active surveillance of drug safety. • SCCS has strengths and weaknesses.  Modifications of the basic model can address some but not all of the weaknesses.  Further research is required to establish the operating characteristics of SCCS-based active surveillance.
  79. 79. Limitations: • As SCCS estimates the exposure-outcome association in cases, it ignores data on individuals in the study population that did not experience the outcome event. • SCCS approach concern the underlying independence assumptions, in particular, the assumption that events are conditionally independent, and the assumption that the exposure distribution and the observation period must be independent of event times.
  80. 80. Methodology: • Self-controlled case series is used by extracting intussusception cases in infants <12 month age from hospital databases (2005-2012) and with vaccination histories from a national immunization registry. • Relative incidences were calculated by comparing incidence during defined risk periods after vaccination with times outside these periods. Risk Period: 1-7 days and 8-21 days after vaccination with day 0 being the day of vaccination. Non-risk period : time period before vaccination and >21 days after a dose of rotavirus vaccine, within the 1- to 12-month age observation period. Intussusception and monovalent rotavirus vaccination in Singapore Self-Controlled Case Series and Risk- Benefit Study - Chee-Fu Yung
  81. 81. Results: Effect of vaccination program at 20% or 90% coverage , compared with no program on hospitalization attributable to rotavirus vaccination Attributable to rotavirus IS in Singapore children,5 years old
  82. 82. Intussusception risk after rotavirus vaccination in U.S. Infants W. Katherine Yih Methodology: Study Population: Children of age 5-36.9 wks to cover recommended vaccination ages (2, 4, 6 months) plus follow-up time and they were member of mini sentinel data partners, Aetna, Health core and Humana between Jan 2004 and Sep 2011. • Cohort and self controlled case series were adopted • Two risk intervals were specified for Rota Teq and Rotarix i.e. 1-7 days and 1-21 days • Medical records were reviewed to validate the vaccine exposures and type of rotavirus vaccination
  83. 83. Cohort Design: •1-21 Days- Exposed person time after rotavirus vaccination. •5-36 wks of age from unvaccinated infants and before and after 0-21 Days of rotavirus vaccination. •Data from the study population itself is used for the age adjustment
  84. 84. Self Controlled case interval design: Risk interval ( or Windows) : 1-7 and 1-21 Days Control interval : 22-42 Days Adjusted for age using the age-specific incidence curve from Tate et al. and a randomization method (As incidence rate of IS varies by week of age)
  85. 85. Rota Teq attributable Risk
  86. 86. Rota rix attributable Risk
  87. 87. Confirmed IS after Rota Teq
  88. 88. Confirmed IS after Rotarix
  89. 89. Conclusion • Evidence of association between IS and Rota Teq was found which was highest in 3-7 days of first dose. • Evidence of association between IS and Rota rix was also found which existed after second dose • Relative Risk Rota Teq -1.12( 95% CI :0.33-2.70) excess cases per 100,000 (7 days after vaccination) Rotarix- 1.54 (95% CI : 0.19-3.22) excess cases per 100,000 (21 days after vaccination)
  90. 90. 3.Case Control study Design: •Compares people who have a disease or adverse event with people who do not and compares exposure to vaccine in each group to determine the relationship between the vaccine and the disease/event.
  91. 91. Case-ControlDesign Study population Cases (disease) Controls (no disease) factor present factor absent factor present factor absent present past time Study begins here
  92. 92. Strengths • Less expensive and time consuming • Efficient for studying rare diseases Limitations • Inappropriate when disease outcome for a specific exposure is not known at start of study • Exposure measurements taken after disease occurrence • Disease status can influence selection of subjects
  93. 93. Methodology:  Population based Surveillance for IS (Dec 2000-Nov 2002) Passive surveillance for hospitalized infants( age< 1years) with IS was conducted in two phases in south Delhi. Age and sex specific estimates were used to calculate the incidence of IS Population-Based Incidence of Intussusception and a Case- Control Study to Examine the Association of Intussusception with Natural Rotavirus Infection among Indian Children -Rajiv Bahl
  94. 94.  The result obtained through passive surveillance were linked with active hospital based surveillance  Case control study of the association between Rotavirus infection and Intussusception Case selection: Infants irrespective of area their area of residence were included for cases (age 2-12 months ) who had a confirmed diagnosis of IS by either Ultrasonography or surgery
  95. 95. Control selection:  Infants (2-12 months of age) admitted to the same hospital as the case patients but do not have the IS  Assessment of case patients and control subjects through questionaire
  96. 96. Active Surveillance: •The community in south Delhi was selected of population ~500,000 •Trained field worker conducted baseline house to house survey to record the age and sex of children ,5 years of age •Total of 11,416 children were identified and their age and sex specific estimates were used as denominator for calculating the incidence of IS
  97. 97. Results: • Intussusception rates obtained ~ 18 cases per 100,000 infant years of follow up • Patients with IS were assessed through ultrasound reported that Rotavirus infection was associated with increased distal wall thickness and lymphadenopathy during illness suggesting a plausible mechanism by which rotavirus infection could cause IS
  98. 98. Limitations • All patients in source population were not covered because they either had died without seeking medical care at hospital or have not accessed it • Less number of patients were included in the study
  99. 99. Case cross over • Study of “triggers” within an individual • ”Case" and "control" component, but information of both components will come from the same individual • ”Case component" = hazard period which is the time period right before the disease or event onset • ”Control component" = control period which is a specified time interval other than the hazard period
  100. 100. • This design was introduced to avoid control selection bias. • Case serves as it own control and it is similar to retrospective cross over design except that the investigator does not control when a patient starts and stops being exposed to the potential trigger.
  101. 101. Source: should we use a cross over design? M Maclure
  102. 102. • A case-crossover design was used. Cases of children were the children admitted with a diagnosis of intussusception hospitals in the city of Valencia, Spain, from 2006 to 2009 (95 cases were selected< 2 years of age) • The association between the episode of intussusception and the intake of prescription medication was assessed. Case period :2, 7, and 15 days (before episode of IS) Control period :for the same time window 1, 2, 3, and 4 months (prior to the episode of IS) Association Between Medication and Intestinal Intussusception in Children: A Case-Crossover Study -Vega Garcia, Lourdes
  103. 103. Results: • The association between the appearance of intussusception in children and medication intake in the immediately preceding period (2–15 days) was assessed • The association between intussusception and prior drug use varied depending on the exposure window: 15-day odds ratio (OR),1.45 (95% CI,0.86–2.43) 7-day OR, 1.46 (95% CI, 0.80–2.67) 2-day OR, 2.26 (95% CI, 1.10–4.64
  104. 104. Thank You