Microbiology Final Study (Epidemiology-)

What did John Snow do?

What did John Snow do?

• English doctor

• Skeptical of the miasma theory of cholera - believed it was carried by water

• In 1854, he used a map to show that cases centered around the Broad street pump

  • Use data to convince the authorities to remove the pump handle

  • A septic tank was leaking into the water supply, causing the cholera

What is Nightingale’s legacy?

She changed hospital design:

• Fresh air

• Clean drains

• Separate wings

Hospital management

• Keep no patient in hospital a day longer than necessary

• The very first requirement in a Hospital is that it should do the sick no harm

Who was Ignaz Semmelweis?

• A Hungarian physician

  • MD degree Vienna 1844

• 1847 - Allgemeine Krankenhaus, Vienna

  • Assistant in obstetrics responsible for the maternity service

  • Observes mortality depended on who delivered the baby

    • 13-18% when delivered by physical or medical students deliver the baby

    • 2% when midwife delivers baby

Father of Infection control

• Mothers died of puerperal fever (child bed fever) which is caused by Strep. Pyogenes

• Required medical students to wash their hands on chlorinated line water

  • mortality dropped from 18.33% to 1.3

  • ‘savior of mothers’

  • Gathered data to convince the administration to change

What is epidemiology

Study of distributions and causes of disease in populations

What are epidemiologists?

Collect, compile data about sources of disease and risk factors

• Design infection control strategie, prevent or predict spread of disease

• Expertise in many disciplines including ecology, microbiology, sociology, statistics, and psychology

what are communicable diseases

Contagious

• Transmitted from one host to anotheħ

  • Measles, colds, influenza, COVID 19

• Transmission determined by interactions between environment, pathogen, and host

  • Control of any of these factors may break infection cycle

    • Improved sanitation

    • Antimicrobial medications

    • Vaccination

What are non-communicable diseases

Do not spread from host to host

• Legionella pneumophila in water systems of buildings

What is the attack rate?

The number of susceptible people who become ill in population after exposure to an infectious agent

What is incidence?

The number of new cases of disease in a population at risk during a specified time period

What is morbidity?

Incidence of disease in a defined population

• Contagious diseases often have high morbidity rates of infected individuals that may transmit to several others

What is mortality?

Overall death rate in population

• The fraction of the people in a population who die

What is an endemic disease?

Constantly present in population - e.g. common cold

What are sporadic diseases?

Few cases from time to time

What is an epidemic?

Unusually large number of cases

• Can be from introduced or endemic disease

What is an outbreak?

Group of cases at specific time and in a specific population

What is prevalence?

The total number of cases at a point in time or a specified period, in a given population

• Expressed as cases per 100,000 people

What is the case-fatality rate?

The proportion of population diagnosed with a specific disease that dies

• Ebola has a very high case fatality rate

What is a pandemic?

Outbreak that spreads to several continents

• AIDS, 19199 Flu, COVID 19

What are human reservoirs?

• Symptomatic infections: obvious source of pathogens

• Asymptomatic infections: harder to identify, carriers may not realize, can spread to others

  • Women infected with Neisseria gonorrhoeae

  • 33% of the population carry Staphylococcus aureus in the nose

What are non-human animal reservoirs?

• Zoonoses exist in animal, can be transmitted to humans

  • Eg plague, rabies

• More severe in humans

What are environmental reservoirs?

Difficult or impossible to eliminate (Clostridium)

What are portals of exit?

Getting to the next host

• Body surface or orifice:

  • Intestinal tract: shed in feces

  • Respiratory tract: exit in droplets of saliva, mucus

  • Skin: shed on skin cells

  • Genital pathogens: semen, vaginal secretions

What is vertical transmission?

• pregnant woman to fetus

• Mother to infant during child birth,, breast feeding

What is horizontal transmission?

Person to person via

• air

• Physical contact

• Ingestion of food or water

• Vector

How is disease transmitted through direct contact?

• From hands, can be ingested: fecal-oral transmission

  • Handwashing considered single most important measure for preventing spread of infectious disease

• Some pathogens cannot survive in the environment, require intimate contact

How is disease transmitted through indirect contact?

• Air: respiratory diseases commonly transmitted

  • Particles larger than 10 um usually trapped by mucus

  • Smaller particles can enter lungs, carry pathogens

  • Talking, laughing, singing, sneezing, coughing generate droplet nuclei

  • Difficult to control

  • Ventilation system, negative pressure, HEPA filters

How is disease transmitted by fomites?

Fomites: inanimate objects

• Clothing, table-tops, doorknobs, drinking glasses

How is disease transmitted by food and water?

Food and water: can become contaminated

• Animal products (meat, eggs) contaminated from animal’s intestines

• Cross-contamination: transfer from one food to another

• Municipal water systems can distribute to large numbers

  • E.g. Cryptosporidium parvum outbreak in Milwaukee, Wisconsin (1993)

How is disease transmission vector-borne?

Vectors: living organisms that can carry pathogen

• Most commonly arthropods: mosquitoes, flies, fleas, lice, ticks; can carry internally or externally

• Can be mechanical or biological

• Vector control important in preventing disease

What is virulence?

The ability to cause disease

• Factors that allow pathogens to adhere to or penetrate host cell, thwart immune defenses, damage host

What is the infectious dose?

Minimum number of pathogens required to cause disease

• Doses below minimum may produce asymptomatic infection

What is the incubation period?

Influences extent of spread

• Long incubation period can allow extensive spread

  • 10,000 individuals drank water containing Salmonella enterica serotype Typhi;

  • 1- to 4-day incubation allowed spread of typhoid fever to at least 6 different countries (1963; ski resort in Switzerland)

What are some characteristics of the host?

• Immunity to pathogen: previous exposure, immunization

  • Herd immunity protects non-immune individuals in population; >90% immunity typically sufficient

  • Antigenic variation can overcome (for example, avian influenza)

• General Health: Malnutrition, overcrowding, fatigue

  • Developing world more susceptible: crowding, poor food, sanitation

• Age: very young, elderly generally more susceptible

  • Immune system less developed in young; wanes in old

  • Elderly also less likely to update immunizations

Descriptive study - data collected following outbreaks - the person

Age, gender, ethnicity occupation, personal habits, etc. may all yield clues about risk

Descriptive study - the place

Geographic location helps pinpoint source, yield clues about potential reservoirs, vectors, etc

Descriptive study - the time

Season important; also rate of spread

• Propagated epidemic: slow rise in cases suggests contagious disease spreading in population; first case is called index case

• Common- source epidemic: rapid rise in cases suggests exposure to single source of pathogen

What is the CDC?

Center for Disease Control and Prevention

• Provides support for infectious disease labs

• Collects data on notifiable diseases

• publishes Morbidity and Mortality Weekly Report (MMWR)

Public Health Departments in each state

• Can mandate which diseases are reported to the state

• Other components of the Public Health Network

• Public schools report absentee rates

• Hospital laboratories report on isolation of pathogens with epidemiological significance

• News media alert public to presence of infectious diseases

What is the WHO and what are the four main functions?

World Health Organization

• Provide worldwide guidance in field of health

• Set global standards for health

• Cooperatively strengthen national health programs

• Develop and transfer appropriate health technology

Provides education, technical assistance

Disseminated information via periodicals, books

• For example, Weekly Epidemiological Record

What are healthcare-associated infections?

Acquired while receiving treatment in healthcare setting

• Patient was not admitted with the disease

One of the top 10 causes of death in United States

• Hospital-acquired or nosocomial infections problematic:

  • Hospitals are densely populated with unusually susceptible people, where resistant and virulent pathogens may exist

• About 5-10% of patients admitted in U.S. acquire

  • About 2/3 are from patients’ own normal microbiota