Epidemiology of Infectious Diseases
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Transcript of Epidemiology of Infectious Diseases
Epidemiology of Infectious Diseases
-Ma. Eufemia M. Collao, MD DPAFP
Objectives: At the end of the session, the student must be able to:
1. Define the following: • sporadic, endemic, epidemic, pandemic, • herd immunity, • attack rates
2. Differentiate:• Communicable from non-communicable
disease• Isolation from quarantine• Mechanical from biological vector• Incubation from generation period
Cont’n…
3. Describe the intrinsic properties of disease agents
4. Discuss the different host agent interaction.
5. Discuss the different pathogenetic mechanism
6. Discuss the different mechanism of transmission.
Infectious Diseases
Also known as communicable diseases.Transmitted directly to man from man (anthropo-zoonoses) or from animals (zoonoses) to man.Characterized by cyclic periodicities and seasonal predilectionsGenetics only an indirect role = predispositions
The EPIDEMIOLOGIC TRIANGLE
MAN
DISEASE AGENT
ENVIRONMENT
Disease Transmission is Affected By :
Factors intrinsic to man
Factors intrinsic to the disease
Role of vectors
Factors intrinsic to the environment
The study of these factors and their dynamics in disease transmission is
EPIDEMIOLOGY
The methodology for this study consists of
Data generation
Data analysis
Evidence-based intervention planning
The main tool used for data generation is
DISEASE SURVEILLANCE
SOURCES OF DATA
FIELD HEALTH SERVICE INFORMATION SYSTEM
PROGRAM-BASED REPORTS
NESS REPORTS
Terms:• Endemic: • Sporadic: occurrence of
disease, on and off, cases seemingly unrelated to each other, low incidence level
• Pandemic: a marked increase in disease incidence of world-wide or continental distribution, usually of sudden occurrence
• Herd immunity: resistance of a group to invasion and spread of an infectious agent
• Secondary attack rate: rate thru which spread of disease is measured
• Secondary attack rate: number of cases of a disease developing during a stated time period among those members of a closed group who are at risk = # of new cases in a group – initial _________case(s)___________# of susceptible persons in the grp –initial cases
EPIDEMICS
Also called outbreaks
Occurrence of a disease over and above its expected levels of occurrence.
Should be qualified by the presence of clustering : chronological and geographic
ESTABLISHNG LEVELS OF OCCURRENCE
Taking the averages (over a period of 3-4 years)
Consider highs and lows
Use of incidence and prevalence
EPIDEMICS
Are calamities in themselves
May result from the occurrence of natural or physical calamities
Occurs as a result of environmental sanitation breakdown, displacement of populations and more conducive environmental conditions for disease prevalence and transmission
NECESSARY…
EARLY DETECTION AND MANAGEMENT OF CASES
SURVEILLANCE : monitor trends
IDENTIFY CAUSE
PLAN PREVENTIVE MEASURES
Origin/ Cause of Epidemics:
New DiseaseIntroduction of disease to the community for the first time
Dse of lower animals affecting man for the first time
Dse discovered for the first time
Old DiseaseIntroduction of new strain of the disease
Immigration of a large number of susceptible individuals
Decrease resistance of population due to catastrophe such as famine, earthquakes, floods, etc
Increased virulence/ pathogenicity
Increased agent population
Termination of Epidemic
Exhaustion of susceptibles
Elimination of the agent
Closure of secondary transmission
Differentiate:
• Communicable vs non-communicable disease
• Isolation vs quarantine• Mechanical vs biological
reservoir• Incubation period vs generation
period
Communicable disease: due to a specific infectious agent or its toxic products, arising through transmission of that agent or its products from reservoir to susceptible host, either directly as from an infected person or animal or indirectly by the agency of an intermediate plant or animal host, a vector, or the inanimate environment; also includes infestation
• Incubation period: from the time the agent enters the host to the time the disease becomes manifest.
• Generation period: period between the receipt of infection by a host and maximal communicability of the host
• Isolation vs quarantine• Mechanical vs biological vector
Describe the intrinsic properties of disease agents
Discuss the different host-agent interaction.
Discuss the different pathogenetic mechanism
Discuss the different mechanism of transmission.
The Ecologic Model of Disease Causation
1. The lever or Balance
Host agent
Environment
The Ecologic Model of Disease Causation
1. The lever or Balance
Host
agent
Environment
Ecologic Model
Host
agent environment
Agent: any element, substance, or force whether living or non-living, the presence of which can initiate or perpetuate a disease process
Types:Living vs non-living
Physical , mechanical
Chemical, nutrients
Characteristics:Inherent: physical features, biologic requirements, chemical make-up, viability, resistance
Those directly related to man: infectivity, pathogenicity, virulence, antigenicity
Those related to the environment: reservoirs and sources of infection and mode of transmission
Those directly related to man
Infectivity: ability to gain access and adapt to the human host to the extent of finding lodgment and multiplication
Pathogenicity: measures the ability of the agent to cause a specific reaction
Virulence: severity of the reaction, usually measured in terms of fatality
Antigenicity: ability to stimulate a response
Different pathogenetic mechanisms
Direct tissue invasion
Production of a toxin
Immunologic enhancement or allergic reaction leading to damage to the host
Persistent or latent infection
Enhancement of host susceptibility to drugs of otherwise minimal toxicity
Immune suppression
Different mechanisms of transmission
Direct transmissionIndirect transmission:
Vehicle-borneVector-borne:
1. Mechanical2. biological
Airborne: 1-5 um1. Droplet nuclei2. Dust
Disease Causation
1. Agent increase in virulence or taken in massive doses2. Agent remains the same but there is a change in the characteristic of the host- a) Decrease in host resistance b) Change in the activity of the host – increase in contact with the diseased person
Isolation & Quarantine
Isolation – separation during the period of communicability of infected persons or animals from others .
To prevent the spread of the disease to those who are susceptible.
Isolation & Quarantine
Categories of Isolation : 7 categories
A) Hands must be washed after contact with the patient or potentially contaminated articles and before taking care of another patient.
B) Articles contaminated with infectious materials should be appropriately discarded or bagged & labeled before being sent for decontamination & reprocessing.
Isolation & Quarantine
Categories of Isolation : 7 categories1. Strict Isolation – to prevent highly contagious and virulent infections that may spread by both air and contact .Specification:Private roomUse of mask , gloves & gown for all persons entering the room.Special ventilation requirements with the room at negative pressure to surrounding areas is desirable
Isolation & Quarantine
Categories of Isolation : 7 categories
2. Contact Isolation –
For less highly transmissible or serious infections
Disease or conditions which are spread primarily by close or direct contact.
Isolation & Quarantine
Categories of Isolation : 7 categories
3. Respiratory Isolation – diseases spread through the air
4. Tuberculosis Isolation-
5. Enteric Precaution
6. Drainage Secretion precaution
7.Blood & Body fluid precaution