Infectious disease part 1

POD winter '26

define infection

process by which a pathogen establishes a parasitic relationship with its host

define colonization

when pathogens are present in the host tissue but aren’t causing symptomatic disease

true or false: the host of an infection can cause further damage to their tissue with their immune response

true

true or false: when a host is colonized, they are able to transit the pathogen to others

true

what are 3 possible outcomes of pathogen transmission?

destruction by innate immunity; subclinical infection and destruction by adaptive immunity; clinically apparent infection with obvious injury to host

what are the 6 parts of the infectious disease chain of transmission?

pathogen, resevoir, portal of exit, transmission, portal of entry, susceptible host

define pathogenecity

the ability of the organism to initiate a disease process

what 3 things does pathogenecity depend on?

pathogen speed of reproduction, extent of damage the pathogen causes to tissue, strength of toxins released by the pathogen

define virulence

how severe of a disease a pathogen can produce, measured by what degree of mortality it causes

(virulence/pathogenicity) provides a quantitive measure of (virulence/pathogenicity)

virulence, pathogenecity

what are the 2 ways a pathogen can present in a host?

clinically symptomatic or as a carrier

what are the 5 modes of pathogen transmission?

contact, airborne, droplet, vehicle, vector-borne

define contact transmission

direct or indirect via a fomite

define airborne transmission

pathogens are propelled from one host respiratory tract to another’s respiratory tract

how small are airborne pathogens?

<5 microns

how long can airborne pathogens be suspended in the air for?

several hours

define droplet transmission

pathogens travel in larger particles up to 3 feet from their source

how large are the particles in droplet transmission?

>5 microns

define vehicle transmission

pathogen transmitted through a common source to many susceptible hosts (ie food or water)

define vector-borne transmission

pathogen uses insects or other animals as intermediaries between hosts

what are 3 very commonly known vector-borne diseases?

malaria, West Nile disease, Lyme disease

define incubation period

time between pathogen entry and appearance of clinical symptoms

when does incubation period end?

when symptoms show up in the host

define latent infection

when pathogen has replicated but remains inactive

how long can a latent infection last?

for years

what are 2 examples of diseases that can be latent infections?

tuberculosis and herpes zoster

define period of communicability

when a pathogen is shed by the host into the environment

when does the period of communicability occur?

towards the end of the incubation period

when can the period of communicability not occur?

in a latent infection

what is a virus?

a subcellular organism made up of RNA or DNA contained in a protein envelope

how are viruses classified? (5)

by size, shape, host, genome, and transmission method

true or false: viruses prefer a host cell, but don’t need one to survive

false

viruses need host cells to ______

replicate

how do antiviral medications mitigate viral illness?

by impairing viral replication

what does gram staining tell us about the bacteria?

which antibiotics will work on that strain

what are bacteria

single-celled organisms with cell walls that can grow independently

how are bacteria classified? (3)

shape, response to staining, need for oxygen

mycoplasmas are a sub-class of _______

bacteria

what are the differences between bacteria and mycoplasmas?

mycoplasmas need a host for nutrition and have no cell wall

mycoplasmas can pass through many bacteria-retaining filters. why?

they are smaller than most bacteria

what are rickettsiae

a small, gram-negative obligate, specific type of bacteria

how to rickettsiae transmit themselves?

via insect bites

true or false: rickettsiae require a host for replication, unlike other bacteria

true

what are chlamydiae

a type of gram-negative, anaerobic bacteria

chlamydiae are (larger/smaller) than rickettsiae but (larger/smaller) than viruses

smaller, larger

what are the 3 subtypes of bacteria we learned about and what do they all have in common?

mycoplasma, rickettsiae, and chlamydiae; all need host for survivalrepl

what do chlamydiae need their host for?

replication

true or false: chlamydiae is not susceptible to antibiotics

false

chlamydiae contain (DNA/RNA/both)

both

what is a protozoa

single celled or group of undifferentiated cells loosely held together with no cell walls

what is an examples of protozoa?

parasitic worms

what are fungi?

unicellular to filamentous organisms with nuclei and cell walls

define mycoses

fungi that infect humans

what is a type of mycoses that lives in the soil in central California and can cause neurological symptoms?

valley fever

what are 2 categories of fungi?

yeasts and molds

what is a prion?

infectious particles consisting of proteins but without nucelic acids

how are prions transmitted?

direct contact with infected tissue

what does “prion disease” cause? what is a well-known example?

mis-folding of normal prion proteins in the brain; mad cow disease

what is the name of an acquired prion disease?

transmissible spongiform encephalopathy

true or false, prion disease can be inherited

true

true or false: prions have a long latent period in the host

true

what are healthcare associated infections?

infections developed by a patient in a healthcare facility that was not present before admission

HAIs affect __ in __ hospitalized people in the US

1, 31

what are 5 causes of HAIs?

invasive monitoring devices, increased exposure to drug-resistance bacteria, exposure to more personnel, greater prevalence of comorbities, poor hand hygeine

What are CLABSIs

central line-associated bloodstream infections

how does a CLABSI develop?

colonization of the device internally or externally

what are the 4 mechanisms of getting a CLABSI?

skin pathogens entering catheter tract; intraluminal contamination with catheter hub manipulation; secondary bloodstream infection contamination; catheter tainted by contaminated infusate

what is a CAUTI?

catheter-associated urinary tract infection

what percentage of CAUTIs are due to indwelling catheters?

70-80

the risk of morbidity of CAUTIs increases with:

more frequent catheter use

how does a CAUTI develop?

biofilm develops around indwelling catheter, causing bacteriuria

which openings can introduce pathogens to a catheter system?

any of them

an external female catheter may reduce CAUTIs, but it does increase:

yeast infections (fungal infection)

what is VAP?

ventilatory-associated pneumonia

define VAP

pneumonia occurring 48-72 hours after endotrachial intubation

what are the 3 criteria of VAP along with the timeline?

signs of infection, gram stain-positive purulent secretions, quantitative growth of pathogen

VAP occurs in what percentage of patients with mechanical ventilation?

5-10

how can PTs help prevent VAP?

early mobilization to reduce duration of mechanical ventilation

what angle should the HOB be to avoid aspiration with VAP?

30-45 degrees

how can an endotracheal tube increase risk of VAP?

prevents closure of epiglottis and thus allows bacterial biofilm to enter the lungs

what is an SSI

surgical site infection

what percent of all HAIs are SSIs?

20%

what are 3 modifiable risk factors for SSIs?

glucose control, obesity, smoking

when you see red streaks, what is that indicative of?

acute lymphangitis

what are petechial lesions

burst capillaries become open sores

what are 6 causes of fever?

hypothalamic abnormalities, brain tumors, dehydration, toxins, infection, immune system response

what populations may not develop a fever in the presence of a serious infection?

older, immunocompromised, or have an HAI

what signs might someone who does not present with a fever present with?

tachypnea, confusion, hypotension

what are the 3 steps to pyrogenic induction of fever?

infection by pathogen, macrophage release of IL-1, hypothalamic heat conservation

what does IL-1 do?

stimulates synthesis of prostaglandin

what does prostaglandin synthesis lead to?

increased “set point” for hypothalamic temperature regulation

why is a fever created?

to make the body an inhospitable environment for the pathogen to be in

what are the 4 types of fever patterns

intermittent, remittent, sustained/continuous, recurrent/relapsing

what is the time frame for intermittent fever?

returning to normal at least once in 24 hours

what are remittent fevers associated with?

upper respiratory infection

what are 5 non-infectious causes of prolonged fever?

drug reaction, pulmonary emboli, neoplasm, tissue necrosis, autoimmune disease

define immunosenesce

immune system declining as you age

what is the root of most of the issues with immunosenescence

degradation of the thymus

what can decreased function of regulatory T cells cause?

low-grade chronic inflammation

what are 3 effects of degradation of the thymus?

reduced diversity of circulating T cells, less stimulation of B cells, reductino in diversity of B cells