AH 3320: Epidemiology and Public Health

Hospital Acquired Infections

- noscomial infections - healthcare acquired infections: new term - MRSA is a very common healthcare acquired infection

New Cases HIV/AIDS (2000-2014)

>3000 deaths per day

Zoonotic Diseases

>60% diseases thought to originate in animals diseases that humans acquire from animal sources

Leading Causes of Global Deaths from Infectious Diseases

respiratory infections and diarrheal diseases

SIR

standardized infection ratio

Historical Epidemics

Of the estimated 250,000 natives in Hispaniola, Columbus' first stop in the Americas in 1492, new infectious diseases (e.g., measles, smallpox, TB) killed a staggering 236,000 indigenous people by 1517 — nearly 95% of their population.

Recent Pandemics

Pandemics occur because viruses have been spread to susceptible populations in areas of the world that had never encountered the viruses before.

World's Deadliest Animal

1) mosquito 2) human 3) snake 4) dog 5) crocodile 6) hippopotamus

COVID-19 Mortality Rate (September 2021)

193 deaths/100,000 in the US

Countries with Malaria Cases (2019)

35 countries account for 98% deaths

Mosquito Transmitted Diseases

- Aedes - Anopheles

Morbidity rate

Number of new cases of a particular disease that occurred during a specified time period per a specifically defined population (usually 100,000 population) Ex.: •Chlamydia in US (2019) = 1,808,703 new cases (incidence) •551/100,000 population; morbidity rate •Morbidity Rate of COVID: 11,873/100,000 (>21 times Chlamydia)

Sporadic Disease

Occurs only occasionally within the population of a particular geographic area

Prevalence of Polio

Period prevalence: -Number of cases of a disease existing in a given population during a specific time period (e.g., during 1988 or 2020 or from 1988 - 2020) Point prevalence: -Number of cases of a disease existing in a given population at a particular moment in time (e.g., right now).

In recent decades...

an average of seven human plague cases have been reported each year (range: 1-17 cases per year)

CAUTI

catheter associated UTI

CLABSI

central line-associated bloodstream infections

Pandemic

disease that is occurring in epidemic proportions in many countries simultaneously •Spanish flu 1918 -- > 20 million deaths (500K in US) •Swine flu (H1N1) 2009 -- > 18,000 deaths (3900 in US) - More than 1000 fold lower than 20 million deaths of Spanish flu

Endemic Disease

one that is always present within the population of a particular geographic area (e.g., the common cold)

CDC data also revealed...

strong declines in Clostridioides difficile (C. diff), likely due to pandemic-related improvements in hand hygiene, personal protective equipment (PPE) practices, and environmental cleaning in the healthcare settings.

VAE

ventilator associated events - went up during 2020

Mortality Rate

•Mortality = Death •Ratio of the number of people who died of a particular disease during a specified time period per a specified population (usually 100,000)

Epidemics (Since 1980)

•Staph toxic shock syndrome •MRSA •AIDS •West Nile virus •Lyme disease •Avian flu •Ebola •Severe acute respiratory syndrome (SARS) •Zika virus •Measles •Cryptosporidiosis •H1N1 influenza •Iatrogenic fungal meningitis •Clostridium difficile •Norovirus •Anthrax bioterrorism •Middle Eastern respiratory syndrome (MERS)

Pertaining to the host

- Health status - Nutritional status - Hygiene - Age - Immune status; immunizations - Lifestyle/behavior

Whether an infectious disease occurs depends on a number of different factors:

- Pertaining to the pathogen - Pertaining to the host - Pertaining to the environment Disease is produced by exposure of a susceptible host to a noxious agent in the presence of environmental factors that aid or hinder agents of disease

Pertaining to the environment

- Physical factors = geographic location, climate, season - Availability of appropriate reservoirs, intermediate hosts, vectors - Sanitary and housing conditions, waste disposal, adequate health care - Availability of potable water

Syphilis Transmission

- Treponema pallidum is a corkscrew-shaped (spirochete) bacterium. - Thrives in most regions of the body and will survive and reproduce only where there is little oxygen present. - It is killed by heat, drying, and sunlight. Therefore, one cannot catch syphilis from contacting toilet seats, bath towels, or bedding.

Epidemiology

- can be loosely defined as the study of disease - Epidemiologists study the factors that determine the frequency, distribution, and determinants of diseases in human populations

Strategies for Breaking Chain of Infection

- eliminate or contain reservoirs of pathogens (if you're sick, stay home) - prevent contact with infectious substances from exit pathways (masks) - eliminate means of transmission - block exposure to entry pathways (wash hands, clean frequently touched objects, avoid touching face) - reduce or eliminate the susceptibility of potential hosts

Staphylococcal Food Poisoning

- food-bourne intoxication - often abrupt and severe in onset - occurs usually 2-8 hours after eating - severe nausea - caused by staphylococcal enterotoxins (protein exotoxins released during growth of Staphylococcus aureus)

Categories of Diseases Caused by Pathogens

- infectious disease: the pathogen causes disease - microbial intoxication: a person ingests the toxin and the toxin causes disease

Hospital Acquired Infections: MRSA

- methicillin-resistant Staphylococcus aureus - caused by Staphylococcus aureus bacteria (staph) - recognized first in hospitals around 1960 - entered wider community in 1990s, where it came to be known as community-associated MRSA or CA-MRSA - dramatic rise of the disease in community reported in recent years - bacteria has evolve to survive common antibiotics (e.g. penicillin, oxacillin, methicillin, amoxicillin) - generally harmless to healthy adults unless enters body through cut or wound

Epidemiologists concerned with:

- who becomes infected - what pathogens cause the infection - where do the pathogens come from - when do certain diseases occur - why do some diseases occur in some place and not others - how are pathogens transmitted

Epidemic vs. Pandemic

As an infectious disease epidemiologist, I've received many inquiries from colleagues and friends about whether a monkeypox pandemic will be the next big disruption to our lives. A disease is considered to be pandemic when two separate conditions are met: cases are occurring globally and the number of cases being diagnosed is large enough to qualify as epidemic. An epidemic is characterized by new cases of a disease occurring at a higher than typical rate in at least several communities.

Historical Epidemics: Syphillis

Columbus brought Syphilis back to Europe after returning from the West Indies. However, its spread within Europe was blamed on the frequent wars within the region at that time. People in one country usually blamed foreigners for introducing the disease. Thus, it was called the "Neopolitan disease" in France, the "French pox" by Italians, and the "French or Spanish disease" by the English. The first documented epidemic of syphilis occurred in western Europe at the end of the 15th century.

Epidemiology: Introduction

Epidemiologists also develop ways to: •Prevent, •Control, or •Eradicate diseases in populations •ALL not just infectious

Historical Epidemics: Smallpox

Great Plains Epidemic of 1837

Microbes: Friend vs. Foe?

Infectious Diseases = leading cause of death in the world (pre-COVID) U.S. (3rd) More than 23 million deaths from Infectious Diseases In developing countries, ½ of infectious disease deaths due to HIV/AIDS, TB, and malaria. Collectively cause > 300 million illnesses and 5 million deaths per year.

Thoughts on what happened to HAI the rest of 2020?

No elective surgeries during COVID Drastic increase in MRSA infections (and bloodstream infections)

Incidence of a particular disease

Number of new cases of a particular disease in a defined population during a specific time period

The Chain of Infection

There are six components in the infectious disease process: •a pathogen •a source of the pathogen (a reservoir) •a portal of exit •a mode of transmission •a portal of entry •a susceptible host

Pertaining to the pathogen

Virulence of pathogen = ability to cause damage to the host Mode of entry (portal of entry) Number of organisms (enough to cause infection) - For example, 1 infectious influenza virus may --> infection - At least 1000 bacteria (gonorrhea)

Epidemic (or Outbreak) Disease

a greater than usual number of cases of a disease in a particular region, usually within a short period of time