CH 14 Infection, Infectious Disease and Epidemiology

Pathogen

Disease causing organisms (infection) in humans (the more virulence an organism has the better the pathogen it is)

Can pathogens vary from person to person?

Yes, some only pathogenic to one person and may be part of another’s personal normal flora

May also vary from human to animal (pathogenic to us but not to animals, vice versa)

Normal Flora/Normal Microbiota

Microorganisms in and on us that makes us who we are → very important

Do not cause disease!!

Microbial Anatogonism

Normal flora that keep antagonists/new/dangerous microorganisms at bay

Function of normal flora → creates hostile environment to new organisms so they may or may not create residency

Protects us!

Opportunists

Some organisms only cause infection in the weak/immunocompromised → example had flu, an ppportunist could come and cause second infection

Middle of pathogenicity

Incidence

Number of NEW cases of a disease over a given/particular period of time

Prevalence

Number of existing (new and old) cases over the same particular period of time as incidence

Sporadic

Pops up in isolation (not related to other cases)

Epidemic

Cluster of cases in a given area (isolated to a singular area)

Ex : measles can turn into an epidemic in one area

Pandemic

Worldwide epidemic like Covid (everywhere in Asia, Europe, America, everywhere)

Endemic

Disease is always around like common cold or strep throat

Disease occurrence

Physicians, Labs, and hospitals are required to report certain infectious disease to the Health Department of the patient’s residency → goes to state → goes to CDC

CDC reports the number of cases of the notifiable disease weekly in the Morbidity and Mortality Weekly Report (MMWR)

Local Infection

Infection in one part of the body ex : bladder infection or urethral infection

Systemic Infection

Infection in many parts of the body

Ex : gnorrhea spreading beyond vaginal canal to cervix or fallopian tubes (can also present as joint pain)

Bacteremia

Mere presence of bacteria in blood

Septicemia

Infection is in blood

Primary infection

Organism causing the first infection

Ex : Flu

Secondary infection

Opportunistic organism causing an infection (a different one than the primary) → only success due to the weak host due to primary infection

Spread of infection

Reservoirs + transmission

Reservoirs

Something that has microorganisms (and then can spread them)

Humans

Animals (Zoonoses)

Fomites

Humans

Human (can be ill, not yet ill, asymptomatic of convalescening aka feeling better)→ to human

Zoonoses

Likelihood of an animal or animal product associated to causing disease

Ex ; cat scratch or bite (pasteurella)

Rabies, salmonella (bacteria through poultry or turtles), cryptococcus (pigeons), E.Coli 0:157 (cattle), Giardia (beavers)

Fomites

Non living réservoirs

Disinfectant targets

Example : door knob, paper towel dispenser, money, cell phones

Human → fomite → human

Transmission

Contact

Vehicle

Vectors

Contact Transmission

Direct contact

Indirect contact

Droplet

Direct contact

Person to person Ex: sexually transmitted diseases

Indirect contact

Fomites

Droplet

Close enough contact (one meter) of another person → close enough to be in contact through air

Ex : a cough, singing, sneeze, organisms can still be transmitted

Vehicle

Waterborne

Food borne

Airborne

Bloodborne

Waterborne

Quickest way to get most people sick in shortest time? Contaminate the water source

Ex : polio, Vibrio Cholera, cryptosporidium parum, Giardia, S. Typhic

Fooborne

microorganisms are in/on fhe food

Ex : Salmonella, E.Coli 0:157, S.typhoc, Mad Cow Disease (Cruizfeld-Jakob prion), Listeria, Shigella; S. Aureus, campyiobacter, hepatitis A, D, Botulism

Airborne

Being propelled more than 1 meter and cause disease

Ex : mycobacterium tuberculosis, legionella premophilia

Blood borne

HIV, Hepatitis B, C, Syphillis, West Nile Virus, Malaria

Vectors

Mechanical : organism is ON the vector, ex : houseflies cockroaches

Biological : organism is IN the vector so when it bites or stings it transfers it, EX: mosquitoes (malaria, Bengue aka yellow fever, West Nile Virus, Zika, Triple E), ticks (Lyme disease, Rocky Mountain fever), fleas (black plague)

Healthcare Associated Infections (HAI)

5-15% of people who seek healthcare intervention/services are expected to come down/suffer with an infection or sickness that they wouldn’t have gotten other wise

HAI factors

1. Microorganism are present in healthcare environments → also typically stronger ones (higher virulence and drug resistant)

2. Opportunity for transmission due to sharing space, equipment, personnel (staff and patients can transmit)

3. Immunocompromised patient population

Old term for HAI?

Nosocomial

Most common HAI

1. Urinary infection

2. Pneumonia

How to try and stop HAI?

Infection control

Infection control

Handwashing

Wearing gloves

Track trends in a hospital (maybe one doctor, need trainings etc)

Spatial requirements (no overcrowding, isolating areas, reverse isolation)

Stages of Infectious Diseases

Incubation period

Prodromal period

Illness

Period of decline

Period of convalescence