EPID 605: Surveillance
Nationally notifiable diseases surveillance system
CDC requests reporting of a number of nationally notifiable conditions. If a state chooses to not report some/all of these conditions, then they cannot receive any CDC funding. The list changes periodically. Official definitions have been published for a number of the diseases/conditions. Some may be clinically diagnosed while others require laboratory confirmation. Reports may be on an individual basis or aggregated. Currently: - 120 diseases under surveillance - Nearly 2.7 million disease events reported annually. - About 3000 public health departments send data to 57 state and territorial health departments who send data to the CDC.
Influenza Surveillance
Complex surveillance system at state, national, and global level. Compiles surveillance data from multiple types/sources.
FoodNet - Foodborne Diseases Active Surveillance Network
Conducts surveillance for Campylobacter, Cryptosporidium, Cyclospora, Listeria, Salmonella, Shiga toxin-producing Escherichia coli (STEC) O157 and non-O157, Shigella, Vibrio, and Yersinia infections diagnosed by laboratory testing of samples from patients. Objectives: - Determine the burden of foodborne illness in the United States. - Monitor trends in the burden of specific foodborne illness over time. - Attribute the burden of foodborne illness to specific foods and settings. - Disseminate information that can lead to improvements in public health practice and the development of interventions to reduce the burden of foodborne illness.
Active Bacterial Core surveillance (ABCs)
Conducts surveillance for group A Streptococcus, group B Streptococcus, Streptococcus pneumoniae, Haemophilus influenzae, Nisseria meningitidis, Methicillin-resistant Staphylococcus aureus (MRSA). Objectives: - To determine the incidence and epidemiologic characteristics of invasive disease. - To determine molecular epidemiologic patterns and microbiologic characteristics of public health relevance for isolates causing the invasive infections. - To provide an infrastructure for further research, such as special studies aimed at identifying risk factors for disease, post-licensure evaluation.
Reporting Structure
County health department reports nationally reportable diseases and state required diseases to the state health department. State Health Department reports nationally reportable diseases and other state specific reporting to the CDC. The CDC reports internationally quarantinable diseases (plague, cholera, yellow fever), weekly influenza activity, and annual summaries of some diseases to the WHO.
Michigan Influenza Surveillance System
- CDC Influenza Sentinel Providers - Sentinel hospitals - MDHHS syndromic surveillance - Severe and fatal influenza case-based surveillance - Laboratory surveillance (Michigan sentinel laboratories, MDHHS laboratory).
CDC Influenza Surveillance
- Laboratory-based system (60 state, city, and university hospital laboratories report weekly influenza virus isolates). - 121-City Mortality Reporting System (121 cities report total # of deaths by age per week and proportion of deaths due to puneumonia or influenza). - CDC Influenza Sentinel Providers (system of sentinel physicians located across the country). - State epidemiologists (state epidemiologists assess the level of influenza and report it as: "no activity", "sporadic", "regional", or "widespread"
Underreporting and Surveillance
All surveillance systems miss cases, so they underreport the amount of disease. Extent of underreporting depends on: - Type of surveillance system - Available resources - Severity of the disease - Sensitivity and specificity of the case definition. - Sensitivity and specificity of the test (if a positive test is required).
Syndromic Surveillance
An investigational approach where health department staff, assisted by automated data acquisition and generation of statistical alerts, monitor disease indicators in real-time or near real-time to detect outbreaks of disease earlier than would otherwise be possible with traditional public health methods. Developed to monitor for bioterrorism, but now expanded. Objective is to identify cases early and to mobilize a rapid response to the outbreak thereby reducing mortality. Uses early clinical symptoms (prodrome). Before clinical or laboratory confirmation of cases. Both clinical and alternative data sources are used.
Surveillance systems of disease indicators
Animal surveillance: - Surveys of rodents for plague - Birds for west nile - Deer and ticks for lime disease Environmental data: - Potential breeding sites or favorable conditions for vectors. Drug/biologic utilization: - Prescription monitoring Student and employee data: - Absenteeism, occupational illness and injuries.
Methods to estimate underreporting
Divide number of cases reported to the public health authorities by total number of cases detected from other sources: - Active case detection, surveys, outbreak investigations, case-control studies. - Does not account for the number of cases undetected by all sources, however. Divide total number of cases reported by the number of cases estimated through use of capture-recapture methods: - Also called under-ascertainment corrected method Community-based cohort studies: - Most direct way - Expensive, may not be representative
Role of surveillance in disease eradication efforts. (Ex. smallpox)
Eradication relied heavily on intensive, active surveillance. Switch from passive to active reporting increased reported incidence of cases. Components: - Reports of cases to health authorities - Regular contact with health care providers - Intensive surveillance where cases occurred. - Rewards ($$) for reporting cases.
What is required to conduct disease surveillance
Legal basis Cooperation between public health officers, clinicians, and laboratories. Resources, including trained personnel, equipment, and software. Reference laboratories, if strains are to be collected. Decision concerning the diseases/conditions to include. Decision concerning the type of surveillance system to employ. Mechanism for/dedication to dissemination of the results to those who provide the data and those in a position to use the data in policy-making.
Role of surveillance in the evaluation of vaccines
Modification of dosing schedule. Evaluate vaccine components. Monitor vaccine administration. Examine vaccine effectiveness.
Uses of surveillance data
Monitoring disease: - Follow long-term trends and patterns in disease. - Detect outbreaks of disease - Identify changes in agents and health factors (such as antigenic change or antibiotic resistance) - Monitor changes in healthcare practices Link to public health action: - Investigation and control - Setting priorities/planning - Evaluating control and prevention interventions - Generate hypotheses and inform research. In class, specific examples given for the following uses: - Estimate magnitude of the problem - Follow long-term trends of patterns. - Describe natural history of the disease. - Determine the geographic distribution of the disease. - Describe the temporal pattern of a disease. - Detect changes in pathogens and recognize emerging infections. - Detect changes in disease patterns requiring explanation/investigation - Monitor treatment practices - Facilitate planning of prevention. - Evaluate public health interventions.
Sources of Surveillance Data
Morbidity reports Mortality reports Outbreak/epidemic reports Laboratory reports Individual case investigations Special surveys (serologic surveys, disease registries). Information on animals and vectors. Demographic data Environmental Data
Surveys of Health and General Population
National Health and Nutrition Examination Survey (NHANES): random sample of the US population. Health Interview Survey: 40,000 households. Behavioral Risk Factor Survey (BRFS): Telephone survey conducted by CDC through collaboration with 40 state health departments.
Morbidity Data
Nationally notifiable disease reports. Laboratory data. Hospital data. Outpatient care data.
Emerging Infections Program
Network of 10 states Represents 44 million people Activities conducted through EIP: - Foodnet - ABCs - Active influenza surveillance - Healthcare Associated Infections-Community Interface (HAIC) projects
Public Health Surveillance
Ongoing systematic collection, analysis, and interpretation of health-related data essential to the planning, implementation and evaluation of public health practice closely integrated with the timely dissemination of these data to those responsible for prevention and control.
Vaccine Adverse Event Reporting System (VAERS)
Passive reporting system for monitoring adverse events due to vaccines. Run by CDC and FDA. Reports of AE come from: - Healthcare providers - Vaccine recipients or their parents. - Vaccine manufacturers.
Active vs. Passive Surveillance
Passive: Routine reporting of cases from health care facilities or clinical/public health laboratories. Active: Surveillance done by searching for cases (door to door, interviewing known contacts).
Sentinel Surveillance Systems
Pre-arranged sample of reporting sources agree to report all cases of one or more diseases. Sources might include: - Individual physicians - Clinics - Hospitals - Laboratories Used to solve the problem of under-reporting or for situations in which complete population-based reporting is not necessary or feasible.
Case Classification
Probable case: A case that meets the clinical case definition, is not laboratory confirmed, and is not epidemiologically linked to another probable or confirmed case. Confirmed case: A case that is laboratory confirmed or that meets the clinical case definition and is epidemiologically linked to a confirmed or probable case.
Rumor Surveillance
Process of investigation of unofficial reports of disease events. Monitoring of rumors from media sources, professional groups, and the public. Involves the timely dissemination of accurate information to reduce misunderstanding and unwarranted concern, especially in the media. Rumors surrounding outbreaks follow Allport and Postman's basic law of rumor: - The amount of rumors in circulation is roughly equal to the importance of the rumor multiplied by the uncertainty surrounding the rumor.
Criteria for Prioritizing Diseases for Surveillance
Rate of the disease: mortality rate, incidence, prevalence Severity of the disease: CFR, YPLL, DALYs, hospitalization rate. Cost Prevention of the disease Communicability of the disease Public and political interest.
WHO Global Influenza Surveillance Network (GISN)
Run through the WHO in collaboration with regional health organizations (e.g. CDC, PAHO, etc.) System of 143 National Influenza Centres (NICs) present in 113 countries. Representative samples of influenza strains are sent in from participating NICs to the CDC (to predict strains for vaccine for next season). Ensures the collection of epidemiological data and or viral isolates for rapid characterization. Objectives: - Monitor the circulating Influenza viruses and make annual recommendations of the influenza vaccine composition for the northern and southern hemispheres. - Detect, as early as possible, unusual influenza strains in human populations, which are of influenza pandemic potential. - Provide, in collaboration with key national reference laboratories, prototype influenza vaccine strains standardizing reagents for influenza vaccine production and testing. Structure of WHO GISN: Sentinel sites (collect samples and epidemiological data) --> WHO Influenza Centres (Isolate representative strains from clinical samples) --> WHO Coordinating Centres (antigenic and genetic analysis of strains) --> WHO (vaccine strain recommendations, diagnostic reagents, potency testing reagents).
CDC recommended surveillance system attributes
Sensitivity: ability to identify cases (all or most) Timeliness: rapidness of reports Representativeness: Likelihood that reporting of disease is same in different subgroups or populations. Positive predictive value: Specificity of case reports Simplicity: structure and ease of operation. Acceptability: willingness of individuals and organizations to participate in the system. Flexibility: ability of system to adapt to changing information needs or operating conditions. Resource requirements.
Detecting traces of infection: seroepidemiology
Seroepidemiology --> investigations involving the identification of antibodies to specific antigens in populations of individuals. This approach can find sub-clinical cases in addition to clinical cases.
Surveillance to define risk groups
Surveillance gathers descriptive data in cases. Data may be used to alter intervention strategies. Data may also lead to epidemiologic studies.
Confidentiality of Data
Surveillance is not research: - Does not require IRB approval - Often a very fine line between when you are doing surveillance or research. Confidentiality: - Data may or may not be confidential (HIV - may be confidential) (TB - not confidential as contract-tracing is needed).
Evaluating Surveillance Systems
Surveillance systems must be efficient and reliable. CDC has a published set of criteria for evaluation. Funding and purpose will largely determine attributes of the surveillance system.
Zoonotic Disease Surveillance
Surveillance systems to detect diseases which are transmitted from animals to humans. Possible components: - Testing of the vector - Testing of wild animals which serve as a reservoir - Sentinel flocks - Website of phone lines to report dead animals. - Reporting from veterinarians.
PulseNet USA
The national molecular sub-typing network for foodborne disease surveillance. Network of 83 labs. Connects foodborne illness cases to detect outbreaks. Molecular epidemiology: DNA Fingerprinting.
Capture-Recapture Method
There is a way to correct the rate of disease based on ascertainment. This was originally developed for ecology. When: N = Estimate of Number M = Number in first sample n = number in second sample m = number of "marked" items in second sample. N = {[(M+1)(n+1)]/(m+1)} - 1 Also write number for 95% CI on notecard!!
Types of Disease Surveillance
Universal case reporting or mandatory reporting: all identified confirmed and/or probable cases of the disease are reported (or should be) by healthcare providers. Laboratory-based surveillance: system where reports of cases come from laboratories instead of healthcare providers/clinics. Sentinel Surveillance: sentinel populations are used for monitoring diseases. (Will typically get better data out of these systems, but will be limited).
Mortality Data
Vital Statistics: - Data on birth, death, marriage, and divorce - Deaths coded by ICD-10 codes Medical Examiner Data: - Includes more details about cause of death than death certificate
