Public Health & Preventive Medicine PMBc303 Lecture 2

Public Health & Preventive Medicine (PMBc303)

• Course: Public Health & Preventive Medicine
• Course code: PMBc303
• Academic year: 2024/2025
• Professor: Reham Elkased

Lecture 2: Introduction to Epidemiology

• Topic: Health
• Topic: Public health
• Topic: Epidemiology

Epidemiology: The Science of Disease

• Definition: A branch of public health that studies disease and its spread in populations (human and non-human). Its aim is to limit pathogens and other negative health issues.
• Greek Origin: Epi - upon, demos - people, ology - study
• Epidemiologists: Often called "Disease Detectives," they investigate the cause of disease, identify those at risk, and find ways to stop its spread and prevent future occurrences.

Pioneers of Epidemiology: John Snow

• 1854 Broad Street Cholera Epidemic: Snow observed that cholera was spread by contaminated water from the River Thames, downstream from London.
• Fecal-oral route of transmission: Water contaminated with sewage and human waste.
• Water pump investigation: he mapped cholera cases and linked infections to a specific water pump on Broad Street.
• Public health response: Local officials removed the pump handle, controlling the epidemic.
• First known public health response to an epidemic.

Epidemiology Triangle

• Agent: The cause of the disease (e.g., bacteria, virus). Factors include pathogenicity and dose.
• Host: The person who can get the disease. Factors include susceptibility, genetic composition, nutrition, and immunity.
• Environment: The surroundings and external conditions that support disease transmission (e.g., climate, insects, crowding).
• Time: Incubation period and duration of illness; time period from infection to epidemic threshold.

Chain of Infection

• Infectious Agents: Bacteria, Fungi, Parasites, Viruses
• Reservoirs: Sources where these agents live, grow, and reproduce (e.g., humans, animals, environment).
• Portal of Entry: How the agent enters the susceptible host (e.g., respiratory tract).
• Portal of Exit: How the agent leaves the reservoir (e.g., respiratory tract, skin).
• Modes of Transmission: How the agent moves from reservoir to host (e.g., direct contact, airborne, vector-borne).

Human Reservoir: Carriers

• Classifications of carriers:
  • Passive carriers (healthy carriers): People who never experience symptoms but can transmit the disease.
  • Active carriers: Infected individuals who may or may not show symptoms.
• Incubatory carrier - shed the microorganism during the incubation period
• Convalescent carrier - shed the microorganism after recovery.
• Incubation period: The time between the entry of the microorganism and the onset of symptoms.
• Convalescent period: The time between the end of symptoms and when the microorganism is no longer present.

Levels of Disease

• Endemic: Constant presence or usual prevalence of a disease in a geographic area (e.g., Hepatitis A, schistosomiasis in Egypt).
• Epidemic: Sudden increase in disease cases above the normal expectancy for a geographic area (e.g., SARS in 2003).
• Outbreak: Same as epidemic, but in a more limited geographic region.
• Pandemic: Epidemic that spreads over multiple countries or continents and affects a large number of people (e.g., Spanish Flu, Covid-19).
• Sporadic: Disease that occurs infrequently and without any geographic concentration.

Epidemic Patterns

• Common source: Outbreak from a single source (e.g., contaminated food/water). Subtypes include point source (exposure within a short time), continuous sources (exposure over a prolonged period), and intermittent sources (exposure that is not continuous).
• Propagated source: Direct person-to-person contact, vehicle-borne, or vector-borne outbreaks (e.g., Hepatitis B, Yellow Fever).

Measures of Disease Frequency

• Incidence: Proportion of people who develop a condition during a specific time period(number of new cases divided by the population).
• Prevalence: Proportion of people who have a condition at or during a specific time (number of cases divided by the population).

Additional Topics

• Portal of exit
• Susceptible host

Dive into the fundamentals of epidemiology with this quiz from PMBc303. Explore the science behind disease spread, the role of epidemiologists, and the historical context provided by pioneers like John Snow. Test your knowledge and understanding of public health and disease prevention strategies.