Outbreak and Surveillance Flashcards
What us meant by Communicable disease?
Disease transmitted from one host to another.
In order for disease to spread a chain of events must occur:
> The pathogen must have a suitable environment in which to live
-Natural habitat is termed reservoir
> The pathogen must leave the reservoir to be transmitted to a susceptible host.
-Organism leaves animal reservoir through a portal of exit
Rate of Disease in population
-Epidemiologists are more concerned with the rate of disease
Rate = percentage of a given population infected
100/10,000,000 vs. 100/1000
- Attack rate is the number of cases developing in a group of people exposed
- 10 people getting sick out of 100 exposed = 10% attack rate
The morbidity rate
is the number of cases of illness divided by population at risk
Mortality rate
reflects the population that dies from disease
Incidence
reflects the number of new cases in a specific time period
Prevalence
reflects the total number of existing cases
Diseases that are constantly present are
endemic
An unusually large number of cases in a population constitutes an
epidemic
Outbreak refers to a
a cluster of cases in a brief time affecting a specific population
When epidemics spread worldwide they are termed a
pandemic
Reservoirs of infectious disease
- Reservoir of pathogens affects the extent and distribution of disease.
- Recognizing reservoirs can help protect the population from disease.
Reservoirs can be:
- Human
- Non-human animal
- Environmental
Human reservoirs
-Infected humans are the most significant reservoirs.
>Primarily of communicable diseases
>In some cases, humans are the only reservoir.
In this case, the disease is easier to control
Human reservoirs as Symptomatic infections and Asymptomatic carriers.
+Symptomatic infections+
- An obvious source of infectious agents
- Ideally infected individuals understand the importance of precautions such as hand washing to inhibit transmission..
-Asymptomatic carriers-
-Individuals harbors pathogens with no ill effects.
-They may shed organisms intermittently for long periods of time
-Some have asymptomatic infection
=More likely to move about spreading the pathogen
Non-human animal reservoirs
- Source of some pathogens
- Disease transmitted by non-human animal reservoirs are termed zoonotic
- Disease often more severe in humans than in normal animal
- Infection in humans is accidental
Environmental reservoirs
-Some pathogens have environmental reservoirs which can include:
>Water
>Soil
-These pathogens difficult or nearly impossible to eliminate
Portals of exit
-Microbes must leave one host in order to be transmitted to another
-Organisms inhabiting the intestinal tract are shed in feces
-Organisms inhabiting the respiratory tract are expelled in respiratory droplets of saliva
-Organisms of the skin are shed with skin cells as they slough off.
#Remember Koch’s postulates
Contact: direct contact.
-In order for the infective process to occur, there must be contact.
Direct contact
- Occurs when one person physically touches another
- Can range from simple contact to intimate contact
- In some cases, direct contact is the primary route of transmission
- Hands are the main vehicle of contact transmission
- Handwashing physically removes organisms. Important in preventing direct contact transmission
-Pathogens that do not survive for extended periods in the environment usually spread by direct contact
Direct: Indirect contact
Indirect contact
- Involves the transmission of pathogens via inanimate objects or fomites
- Usually clothing, tabletops, doorknobs, and drinking glasses
- Organisms on the hands or fingers of the carrier can be transferred to objects and picked up by another individual
- Handwashing is an important control measure
Droplet transmission
- Microbe-laden respiratory droplets generally fall to the ground within three feet of release
- People in close proximity can inhale infected droplets spreading disease via droplet transmission
- Droplet transmission considered direct transmission because of the close range required for transmission
Food and water transmission
Food and water
- Pathogens can be transmitted through contaminated food and water
- Food can become contaminated in a number of different ways
- Organisms can originate with animal
- Organisms can be inadvertently added during food preparation
- Cross-contamination occurs when organisms from one food are transferred to another from an improperly cleaned work surface
- Cutting boards and knives
- Sound food handling practices can prevent foodborne transmission and disease
Waterborne disease
- Waterborne disease outbreaks can involve large numbers of people
- Due to the fact that municipal water is distributed to large areas
- Prevention of waterborne diseases requires chlorination and filtration of public water sources and proper disposal of sewage
Air transmission
Air
-Respiratory droplets can be transmitted through the air
-Smaller droplets dry in the air leaving one or two organisms attached to dry material
-Creates droplet nuclei
=Droplet nuclei can remain suspended indefinitely in presence of light air currents
->Airborne transmission is difficult to control
-Ventilation systems aimed at circulating air in buildings
: HEPA filters are effective at removing airborne organisms
: Airline ventilation is notoriously bad
Vector transmission
Control of vector-borne disease directed at controlling arthropod population.
- Any living organism that can carry a disease-causing microbe.
- Most common are arthropods.
- Vector may carry organism internally or externally.
Portals of Entry
Portals of entry
-Pathogen must enter and colonize new host
-Colonization is prerequisite for causing disease
-Route by which pathogen enters body is termed portal of entry
-Major portals of entry include”
Eyes
Ears
Respiratory tract
Broken skin
Digestive tract
Genitourinary tract
Factors that influence the epidemiology of diseases.
- Dose
=Probability of contracting the disease is often proportional with the dose
-Minimum number of bacteria required to establish disease - Incubation period
=Disease with a long incubation period can spread extensively before the first case
appears - Population characteristics
- Certain populations are more susceptible than others to certain pathogens
- Demographic factors paramount: socio-economic status etc.
Population characteristics that influence the occurrence of disease
- Immunity to pathogen
- Previous exposure or immunization of population decreases the susceptibility of the population to the organism
- Can lead to herd immunity
- Unimmunized protected due to lack of reservoir of infection
- General health
- Stressors such as malnutrition or overcrowding increases the susceptibility of the population - Age
- Very young and very old tend to be at greater risk
- Young due to under developed immune system
- Old due to waning immune system
More population characteristics that influence the occurrence of disease
- Gender
Gender influences disease distribution
Often due to anatomical differences - Religious and cultural practices
- Cultures that routinely breastfeed babies see less infectious disease in children - Genetic background
- Natural immunity can vary with genetic background
- Difficult to assess the relative importance of genetics
Epidemiological Studies
-Epidemiologists investigate disease outbreak to determine:
>Causative agent
>Reservoir
>Route of transmission
-Allows them to recommend ways to minimize the spread
Population Health Surveillance Systems
-Special health information system
-Detect new risks and diseases
-Track old problems
-Generate timely and useful data to:
>Plan
>Allocate resources
What does surveillance actually mean?
- According to Napoleonic wars it is ‘the constant watching of subversives’.
- Watching diseases in populations – public health surveillance.
Watching people – medical surveillance:
- Close contacts of infectious people who have been isolated/quarantined watched until the end of the incubation period to interrupt community transmission.
- Those who come from an area with an epidemic e.g. SARS and swine flu … thermal screening and check of respiratory systems.
Public health surveillance
Public health surveillance is the ongoing systematic collection, analysis, interpretation, and dissemination of health data
Use surveillance data to describe and monitor health events, set priorities, and to assist in the planning, implementation, and evaluation of public health interventions and programs
Purpose: provide a factual basis from which one can promote and protect the public’s health
Surveillance systems
> Networks of people & activities
—Local, national, international
> For the effective control and prevention of:
- Diseases
- Their determinants
Surveillance systems are often considered information loops or cycles involving health care providers, public health agencies, and the public, The cycle begins when cases of the disease occur and are reported by health care providers to the public health agencies
The components of surveillance and resulting public health action
Surveillance > Collection > Analysis > Interpretation > Dissesmination
Public Health Action
*Priority setting
> Planning, implementing and evaluating disease
- Investigation
- control
- prevention
History (of surveillance)
14th Century – efforts to control bubonic plague in Europe
Farr (1839 – 1870) – Collected data on causes of death and published a collection of papers on ‘Vital Statistics’
1919 – following influenza epidemic in SA, certain diseases were made notifiable
Langmuir (1963) – first introduced the concept of surveillance as the monitoring of disease occurrence in the population - Known as public health surveillance
1968 – Smallpox eradication - Used active surveillance and targeted interventions
Functions of disease surveillance.
- Estimate the magnitude of the problem
- Determine the geographic distribution of the disease
- Portray the natural history of the disease
- Detect epidemics/define a problem
- Generate hypotheses, stimulate research
- Evaluate control measures
- Monitor changes in infectious agents
- Detect changes in health practices
- Facilitate planning
Sources of Data
Mortality reports
Morbidity reports
Epidemic reports
Reports of laboratory utilization (including laboratory test results)
Reports of individual case investigations
Reports of epidemic investigations
Special surveys (e.g., hospital admissions, disease registers, and serologic surveys)
Information on animal reservoirs and vectors
Demographic data
Environmental data
Types of Surveillance
- Passive
- Active
- Sentinel
- Outbreak investigation
Passive Surveillance
- Health Care Provider initiated/Laboratory-based
- Routine reporting of notifiable diseases
- Every case of a particular condition must be reported
- DOH solicits reports on diseases that constitute a danger to public health
- Statutory obligation
- Reported orally and communicated in writing within 24 hours
- Weekly returns including nil returns
- Inexpensive but less complete
- Underestimates true disease burden
- Monitors patterns and changes over time, across regions, amongst different groups of people
- Good for conditions that have clear symptomatology
Active Surveillance
- Initiated by DOH
- Based on a specific collection of data- as the need arises
- Useful for diseases that can easily be missed
- Produces more complete data, of better quality
- But resource-intensive to maintain and to produce timely reports
Outbreak investigation Surveillance
> > Outbreak
-Affects fewer people, shorter duration, localized
CDC- “the occurrence of 2 or more cases which are epidemiologically related”
> > Epidemic
-Occurrence of the disease at a level in excess of background incidence for the defined group during a particular season and time period.
What are the CATEGORY 1 NOTIFIABLE MEDICAL CONDITIONS?
Require immediate reporting by the most rapid means available upon diagnosis followed by a written or electronic notification to the Department of Health within 24 hours of diagnosis by health care providers, private health laboratories or public health laboratories
Examples of Category 1 - Notifiable medical condition
- Food-borne disease outbreak is the occurrence of two or more cases of a similar foodborne disease resulting from the ingestion of a common food.
- *Examples of novel respiratory pathogens include novel influenza A virus and MERS coronavirus.
- ** Viral hemorrhagic fever diseases include Ebola or Marburg viruses, Lassa virus, Lujo virus, new world arenaviruses, Crimean -Congo hemorrhagic fever or other newly identified viruses causing hemorrhagic fever
Others include: Acute flaccid paralysis Acute rheumatic fever Anthrax Botulism Cholera Diphtheria Enteric fever (typhoid or paratyphoid fever) Meningococcal disease Pertussis Plague Poliomyelitis Rabies (human)
CATEGORY 2 NOTIFIABLE MEDICAL CONDITIONS
Category 2 notifiable medical conditions to be notified through a written or electronic notification to the Department of Health within seven (7) days of clinical or laboratory diagnosis by health care providers, private health laboratories or public health laboratories
Examples of Category 2 notifiable medical conditions
Agricultural or stock remedy poisoning
Bilharzia (schistosomiasis) Brucellosis
Congenital rubella syndrome Congenital syphilis Haemophilus influenzae type B
Hepatitis
Maternal death (pregnancy, childbirth, and puerperium)
Leprosy
Mercury poisoning
Soil-transmitted helminths Tetanus
Tuberculosis: Pulmonary Tuberculosis: extra-pulmonary Tuberculosis: multidrug-resistant (MDR-TB) Tuberculosis: extensively drug-resistant (XDR-TB)
Lead poisoning
Legionellosis
CATEGORY 3 NOTIFIABLE MEDICAL CONDITIONS
-Through a written or electronic notification to the Department of Health within 7 days of diagnosis by private and public health laboratories
Examples of Category 3 notifiable medical conditions
Ceftriaxone-resistant Neisseria gonorrhoea
West Nile virus
Sindbis virus
Chikungunya virus
Dengue fever virus
Other imported arboviruses of medical importance
Salmonella spp. other than S. Typhi and S. Paratyphi
Rubella virus
Shiga toxin-producing Escherichia coli
Shigella spp
CATEGORY 4 NOTIFIABLE MEDICAL CONDITIONS
Through a written or electronic notification to the Department of Health within 1 month of diagnosis by private and public health laboratories
Healthcare-associated infections or multidrug-resistant organisms of public health importance
- Carbapenemase-producing Enterobacteriaceae
- Vancomycin-resistant enterococci
- Staphylococcus aureus: hGISA and GISA
- Colistin-resistant Pseudomonas aeruginosa
The Notification Process in SA
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The Notification Process in SA
Slide 42
Types of Active Surveillance
- Facility-based
Throat swab specimens – isolation and monitoring of influenza viruses - Household surveys
Serological detection of malaria – detect asymptomatic malaria carriers to reduce the prevalence of parasite carriers - Special surveys
For new or unusual disease problems
MDR TB, XDR TB
Sewer pads for active surveillance of cholera in water sources
Why do we investigate outbreaks?
> Outbreak investigations help to establish the source/cause of the outbreak
>Purpose: to target interventions >Provides information on: -Vaccine efficacy -Age-specific attack rates -Age-specific case fatality rates
> Institute control and prevention measures
Provide the opportunity for research and training
Public relations, political concerns, and legal obligations
Steps in Outbreaks investigation
- Confirm the outbreak and prepare for fieldwork
- Establish a Case definition
- Describe the Outbreak
- Develop and test the hypothesis
- Implement Control Measures
- Report writing
- Distribute report
- Confirm the outbreak and prepare for fieldwork
regular analysis of surveillance data increased incidence: improved case detection improved reporting change in diagnostic criteria, false positive laboratory test: review the clinical findings and lab results
- Establish a Case definition
Standard set of criteria for deciding whether an individual should be classified as having the health condition of interest
Includes clinical criteria and restrictions by time, place, and person
Not a case, possible, probable, confirmed
- Describe the Outbreak
- Person
Age, sex, occupation, SES and immunization
2. Place Home address, work address, school Recent travel Any function attended Plot spatial location on a spot map – demonstrates clustering of cases and provide clues about exposure (e.g. GIS)
- Time
- Drawing a histogram - number of cases by their date of onset
- Epidemic curve gives a simple visual display of the outbreak’s magnitude and time trend
- Common exposure at a single point in time – point source epidemic – steep curve, short duration
- Exposure over a period of time propagated – broader, shallower epidemic curve
Case definition - TB
- Possible/Suspected case
=Persistent cough > 3 weeks, LOW, blood present in the sputum, night sweats - Probable case
On auscultation abnormal lung sounds. Positive TST. Abnormal CXR (interpreted in the light of history and clinical findings) - Confirmed case
Laboratory confirmation: positive sputum test i.e. presence of AFB when stained with ZN acid stain. In MDR - a culture is done, stained again for the presence of AFB, and bacilli are exposed to various TB medications - Not a case
Does not satisfy any of the criteria stated above
- Develop and test the hypothesis
> The hypotheses should address the source (agent) of the epidemic, the mode (and vehicle or vector) of transmission, and the exposures that caused the disease
> Environmental and microbiological investigations
> Analytic epidemiology – measuring associations between disease and exposure
-Need a comparison group
-Data collection, if feasible from each case and control
>Case interviews
>Standardized questionnaires
- Implement control measures
- Short term
>break chain of transmission, to prevent new cases from developing
-Long term
>deal with the underlying causes of the epidemic
Standardized questionnaire
Symptoms (related to case definition)
Precise date of onset
Demographic characteristics
Events attended/places visited (exposures)
Time and place of contact with other possible cases
Sources of water
Leisure activities
Sexual history
Recent travel history
Occupational history
Contact with animals
Signs and symptoms of bites or rashes
Immunization history and history of previous infectious diseases
Medical history of diseases that may affect the immune system
- Report writing
- Background to the investigation
- Description of the epidemic: person, place, and time
- Hypotheses considered and laboratory evidence supporting or refuting the hypothesis
- Conclusions as to the cause, source, and mode of transmission
- Recommendations:
- Short-term and long-term
Problems with Surveillance
- Poor understanding of the importance of notification
- Poor knowledge of conditions and definitions of cases
- Competent to diagnose => required to report
- Form too complicated
- Lack of feedback
- Poor training in surveillance
- Lack of resources
