Lec+10+Principles+Infec+Dis+%26+Epi+2024+v2

case fatality rate vs mortality rate

case fatality rate (CFR, severity) = # of deaths / time

mortality rate: # deaths/time period

attack rate

the proportion of people who become ill with a disease in an at-risk population initially free of the disease (from beginning to end of an outbreak)

endemic vs epidemic vs pandemic vs sporadic

chain of infection

Certain conditions must be met in order for a microbe or infectious disease to be spread from person to person.

can only occur when all six links in the chain are intact. By breaking this chain at any of the links, the spread of infection is stopped

definitive vs intermediate host

Definitive host – protist or helminth attains maturity or passes sexual stage

Intermediate host – protist or helminth is in larval or asexual state

types of reservoirs

human: carriers

animal: zoonoses

environmental: soil (bacteria), water

reservoir vs non-reservoir

reservoirs does not experience the symptoms of disease when infected by the pathogen, whereas non-reservoirs show symptoms of the disease

how microorganisms enter the body

Skin (including percutaneous, bites, wounds,burns)

Eyes (e.g., bacterial, viral)– Gastrointestinal tract

Respiratory tract

Urogenital tract

Placenta

Portal of entry can be important

Yersinia pestis: pneumonic versus bubonic

where microorganisms leave the body

Body fluids

Feces

Respiratory

airborne droplets

Urine

Semen

Blood (transfusion, accidental needle-stick, IVDU)

Milk

modes of transmission

Direct Transmission -- direct contact

• horizontal

  • direct contact

  • direct projections

• vertical

  • congenital

  • perinatal

Indirect Transmission:

• direct exposure to agent in soil, infected animal

• Vehicle-borne

• Vector-borne

  • Mechanical

  • Biological

Airborne Transmission

Sexually transmitted

direct transmission of disease

Horizontal

• Direct contact -- touching, biting, kissing or sexualintercourse

• Direct Projections -- droplet spray onto mucousmembranes of conjunctiva, eye, nose or mouth duringsneezing, coughing, spitting, or talking (<1 meter)

Vertical:

• Congenital -- congenital disorders are structural and functional defects present at birth and are the result of cross-placental infection

• Perinatal – shortly before, during, and after birth

• Direct exposure to agent in soil, infected animal in placenta

indirect transmission of disease

Vehicle-borne (no multiplication in or on vehicle)

• Contaminated fomites (inanimate materials or objects)such as toys, handkerchiefs, clothes, bedding, cooking or eating utensils, doorknobs, elevator buttons

• Water (e.g., fecal-oral)

• Food (e.g., fecal-oral)

• Milk

• Biological products (blood, plasma, organs)

• Inoculation, injection, piercing

Vector-borne: arthropods that transmit diseases tohumans, e.g., ticks, flies, fleas, lice, mosquitoes

• Mechanical vectors (e.g., flies and Vibrio cholerae)

  • Transmission passively

  • Disease transmission does not require replication inthe vectors

• Biological vectors (e.g., mosquitoes and dengue virus)

  • Active transmission–

  • Pathogen replicates in vector; often necessarycompletion of microbial life cycle in vector

  • An incubation period is required before transmissionof infective form

airborne transmission of disease

dissemination ofmicrobial aerosols to a suitable portal of entry, usually by the respiratory tract

• Aerosols – small residue result from evaporationof fluid from droplets

  • Particles 1-5 um are easily drawn into the alveoli of lungs, remain suspended for long periods

• Dust, soil particles small droplets - can be drawn
  

R_o

reproductive rate

the number of people that one sick person will infect is

host microbe relationships

Mutualism: both benefit (bacteria in digestive tract, vitaminK)

Parasitism: parasitic microbe benefits, host is harmed (Note: spectrum—slight harm to death)

Commensalism: one species benefits, other neither benefits nor is harmed skin bacteria

Antagonism: both species harm each other

levels of host-microbe relationships

Colonization – “normal flora”

Infection – replication of any parasite in or on the host

Subclinical/asymptomatic infection

Disease – any disturbance of the normal functioningof the host by parasite

types of pathogens

pathogen: An organism that is capable of causingdisease

Non-pathogen: An organism that is not usuallycapable of causing disease

Opportunist: An organism that only causes diseasewhen the host is compromised

• AIDS

• Immunosuppressive drugs

iceberg concept of infection

metaphor used in epidemiology and public health to illustrate the spectrum of disease severity and the proportion of cases that are visible versus those that are hidden. This concept helps in understanding that the cases of disease we see (the tip of the iceberg) are only a small fraction of the total number of cases that actually exist.

incubation period

he time interval between initial contact with an infectious agent and the first appearance of symptoms associated with the infection

epidemiologic triad

microbial virulence

capacity of an infectious agent, compared together closely related infectious agents, to produce disease in a host. Virulence depends on a variety of microbe and host factors

types:

Entry and adhesion

Colonization and infection

Invasion

Exotoxins

Endotoxins

host pathogen co evolution

pathogens evolve to maximize their transmission and survival

If severity decreases the likelihood of transmission (e.g., by reducing host mobility), then less virulent pathogens will be favored. Pre-mature death of host can result in death of virus and can lead to non-transmission.

If virulence aids transmission (e.g., extreme fluid release of diarrheal diseases, coughing in respiratory diseases)then the more virulent pathogens will out-compete

Attenuation (weakening) by sub-culturing on/in laboratory

infectivity

Entry – Adherence

• Specific molecules for adherence to host cells

Colonization and Infection

• Nutrient availability – e.g., the battle for iron

• Host: transferrin, lactoferrin

• Bacterial pathogens: siderophores

toxins (microbial virulence)

potent poisons produced bymicroorganisms

• Destroy host cells

• Interfere with normal function– Many exotoxins are phage-encoded

Two main types of toxins

• Exotoxins (proteins

  • Toxic proteins released from growing cells; generally heat labile

  • Travel from site of infection and cause damage at distant site

    • Subset of exotoxins – enterotoxins – exotoxins affecting the gastrointestinal tract, usually small intestine

  • types

    • cytolytic toxins

    • AB toxins

    • superantigen

• Endotoxin (LPS)

  • Gram negative bacteria – LPS

  • Cell bound, released when cell lyses

  • Heat stable

host factors

Genetics– cell receptors– genetic traits (sickle cell trait and malaria)– HLA type (MHC)

Age: old and young usually more susceptible

Gender – e.g., structure of urinary tract (UTI)

Pregnancy

Nutritional status

Co-morbidities: obesity, diabetes, hypertension

Hormonal balance– Glucocorticoids can depress immune system (stress, lack ofsleep)

Integrity of organ system

• Abnormal urinary tract predisposes to urinary tract infections

• Smoking can predispose to respiratory tract infections

Integrity of immune system – immunocompromise

Immune status: previous exposure or vaccination

Behavior: smoking, diet, drinking, sexual practices,exercise

Structural inequities affect risk factors for infectious diseases

Lack of access to nutritious foods in inner cities, presence of processed foods, sodas obesity

RF plus lack of access to health care hypertension, diabetes

lack of access to hospitals/ICUs

unplanned urban settlements with poor waste and sanitation

Environmental Factors for infectious diseases

Physical

• Weather, climate, geology

• Ecological zone

Biological

• Sources of food, water, and air–

• Presence of vectors, flora and fauna

Social and cultural

• Density, crowding, adequate housing, war,sanitation, availability of health care

Agricultural practices

primary prevention of diseases

Methods to avoid occurrence of disease.

Most population-based health promotion efforts are of this type

secondary prevention of disease

methods to diagnose and treat existent disease in early stages before it causes significant morbidity.

how to interrupt Chain of Infection

Eliminate source of agent

Prevent further exposures– Detect & treat cases

Personal hygiene: hand-washing, control coughing, sneezing, prevent airborne transmission

Disposable needles

Safe drinking water (hand-washing)

Waste-handling, management

Proper food-handling

Barriers: condoms, bed nets, respiratory