1. The study of Communicable diseases and their prevention
Epidemiology
The study of Communicable diseases and their prevention

2. Bacteria E. coli H. Pylori
Source: Department of Microbiology, The Chinese University of Hong Kong

3. Viruses Hepatitis B virus
Source: Department of Microbiology, The Chinese University of Hong Kong

4. Fungi
Aspergillus
Source: Department of Microbiology, The Chinese University of Hong Kong

5. Protozoa
Entamoeba
Source: Department of Microbiology, The Chinese University of Hong Kong

6. Roundworms Ascaris (adult)
Source: Department of Microbiology, The Chinese University of Hong Kong

7. Principles of Epidemiology
Communicable disease
Disease transmitted from one host to another
In order for disease to spread, a chain of events / infection must occur
Pathogen must have suitable environment in which to live
Natural habitat is termed reservoir
Pathogen must leave reservoir to be transmitted to susceptible host
Organism leaves animal reservoir through portal of exit

8. Chain of infection

9. Reservoir and Carrier 1. Reservoir 2. Carrier
A reservoir is the source of an infecting microorganism.
It can be anything e.g. Animal, vegetable, soil human
2. Carrier
Intraspecific reservoirs may also be referred to as carriers. i.e. human

10. Carrier -- Intraspecific reservoir
A carrier is a person who carries a communicable disease and serves as an "intraspecific" reservoir.
Overall, carriers are the most important reservoirs of human disease.
Asymptomatic carriers WHO? WHEN?:

11. Carrier -- Intraspecific reservoir
Asymptomatic carriers WHO? WHEN?:
During the incubation of and recovery from an infection, a person can still be the carrier of some diseases.

12. Portals of entry Pathogen route of entry:
A portal of entry is the route a pathogen takes to enter a host.
Typical routes include: mucous membranes, skin, wounds
IMPORTANCE?

13. Portals of entry IMPORTANCE?
Just as with portals of exit, many pathogens have preferred portals of entry.
Many pathogens are NOT able to cause disease if their usual portal of entry is artificially bypassed.

14. Portal of exit -- Route out of body:
A portal of exit is the route a pathogen takes out of an infected host.
Respiratory infections eg?
Gastrointestinal infections eg?
Sexually transmitted diseases eg?
Blood-borne diseases via: eg?

15. Portal of exit -- Route out of body:
A portal of exit is the route a pathogen takes out of an infected host.
Respiratory infections --mouth and nose
Gastrointestinal infections feces or saliva
Sexually transmitted diseases urethra or genital region.
Blood-borne diseases via: arthropods, needles* bleeding , surgery

16. Portal or entry and Portal of exit

17. Route of transmission
the transfer of a disease-causing microorganism from one environment to another, particularly from an external environment to a susceptible individual.
For example, from a portal of exit to a portal of entry.

18. Principles of Epidemiology
Transmission
Successful pathogen must be passed from reservoir to next susceptible host
Transmission of pathogen via contact with food, water, or living agent is termed horizontal transmission
Transmission via transfer of pathogen from mother to fetus or child through breast feeding is termed vertical transmission

19. Principles of Epidemiology
Contact
Direct contact
one person physically touches another
from simple contact to intimate contact
Hands are main vehicle of contact transmission
What do you expect of pathogens that spread mainly by direct contact? Prolonged survival in environment?
Pathogens that do not survive for extended periods in the environment usually spread by direct contact
Indirect contact
via inanimate objects
Usually clothing, tabletops, doorknobs, and drinking glasses
Handwashing: important control measure

20. Principles of Epidemiology
Droplet transmission
Respiratory aerosols
Vomiting
Diarrhea
Food and water
Vectors
Any living organism that can carry a disease- causing microbe
Most common are arthropods
Vector may carry organism internally or externally

21. Acquisition of Disease
for individual pathogens, both the source (reservoir) and the method of transmission are fairly limited. WHY?
Often disease can be and is prevented by specific blocks on pathogen transmission. HOW?

22. Acquisition of Disease
for individual pathogens, both the source (reservoir) and the method of transmission are fairly limited. WHY? This is because pathogens tend to have evolved one or, at most, only a few methods of acquisition of a host.
Often disease can be and is prevented by specific blocks on pathogen transmission. HOW? Often these blocks involve reservoir elimination, prevention of direct contact with the reservoir, or interruption of chains of contact between the susceptible person and the reservoir.

23. Principles of Epidemiology
Diseases that are constantly present are endemic
Unusually large number of cases in a population constitutes an epidemic
When epidemics spread worldwide they are termed pandemic
Outbreak refers to a cluster of cases in a brief time affecting a specific population

24. Principles of Epidemiology
Factors that influence epidemiology of disease
1. Dose
Probability of contracting disease is often proportional with dose
2. Incubation period
Disease with long incubation period can spread extensively before first case appears
3. Population characteristics
Certain populations are more susceptible than others to certain pathogens

25. Principles of Epidemiology
Population characteristics that influence occurrence of disease
1. Immunity to pathogen
Previous exposure or immunization of population decreases susceptibility of population to organism
Can lead to herd immunity
Unimmunized protected due to lack of reservoir of infection
2. health
Stressors such as malnutrition or overcrowding increase susceptibility of population
3. Age
Very young and very old tend to be at greater risk
Young due to underdeveloped immune system
Old due to waning immune system

26. Principles of Epidemiology
3. Population characteristics that influence occurrence of disease
Gender
Gender influences disease distribution
Often due to anatomical differences
Religious and cultural practices
Cultures that routinely breast feed babies see less infectious disease in children
Genetic background
Natural immunity can vary with genetic background
Difficult to assess relative importance of genetics

27. Epidemiological Studies
Epidemiologists investigate disease outbreak to determine
Causative agent
Reservoir
Route of transmission
Allows them to recommend ways to minimize spread

28. Infectious Disease Surveillance
International agencies include
Centers for Disease Control and Prevention (CDC)
World Health Organization

29. Trends in Disease Reduction and eradication of disease
Humans have been very successful at developing ways to eliminate or reduce disease
Efforts have been directed at
Improving sanitation
Reservoir and vector control
Vaccination
Antibiotic treatment
Smallpox has been globally eradicated as a disease

30. Trends in Disease
U. S. death rate from infectious diseases per 100,000 population per year

31. Trends in Disease Emerging and Re-emerging diseases
Organisms equally adept at taking advantage of new opportunities of infection
New diseases emerge
Increase in incidence in past two decades
Old controlled diseases make a comeback

32. Trends in Disease
Factors that contribute to emergence and reemergence include
Microbial evolution
Complacency and breakdown of public health
Abusive use of antibiotics
Population expansion
Advances in technology How?
Mass distribution and importation of food
War and civil unrest
Climate changes

33. Infections acquired in Hoapital
Reservoirs of infectious agents in hospitals
Other patients
Patients can harbor infectious agents and discharge into environment
Hospital environment
Certain bacteria do not require many nutrients and can survive long periods on surfaces
Many of these organism are antibiotic resistant
Due to continual exposure to antibiotics
Health care workers
Outbreaks can sometimes be traced to hospital worker
Often as a result of improper handwashing or sterile technique
Patient’s own normal flora
Invasive treatments often introduce surface flora to interior regions of body

34. Transmission of infectious agents in hospitals
Medical devices
Devices routinely breach first-line barriers
inadequately sterilized instruments
Healthcare personnel
Handwashing between patients effective against spread of disease
Airborne
Airflow is regulated to specific parts of hospital
Keeps certain areas contained