Lecture 3 transmission of infection and principles of disease Flashcards
Where are the portals of exit?
identical to entry
Exiting can be through coughing, sneezing, saliva, sputum
Pathogens also leave via blood, vaginal secretions, semen, urine, and faeces
Pregnant women and babies infection note:
Unique interactions between mother and the foetus
What affects spread of infection?
Reservoirs (places where pathogens grow and accumulate)
Mechanisms of transmission (ways pathogens move)
What are some potential reservoirs for pathogens?
Humans
Other animals
Non-living reservoirs such as water food and soil
How can humans and other animals be as reservoirs?
Sick people show symptomsa and are easy to identify but difficult when symptoms are yet to develop or have ceased
Carriers of infection can transmit disease but show no symptoms
How can non-living reservoirs move disease around?
Water is a necessity and can hold pathogens
Leading to high levels of faecal contamination in water can lead to infections spreading via faecal oral route
How can infection be spread?
Contact
Vehicle
Vector
What are the types of contact transmission?
Direct (touching)
Indirect (touching something someone else touched)
Droplets (airborne)
What is a commonly touched item that causes infectious disease transmission called?
A fomite
What are some pathogens transmitted through direct contact?
Staph
Hep A
Smallpox
STIs
What are some examples of indirect contact transmission?
Sharing of needles HIV
Snotty tissue transmission
What pathogens are often transmitted by droplets?
Influenza and whooping cough
What factors are important to droplet transmission?
Distance (short distance more likely to transmit)
Size (large droplets fall to the ground quickly smaller droplets stay airborne for a while)
What is vehicle transmission?
Can involve pathogens riding along on air food water and this enters body and transmits infection
How is air used as a vehicle?
Spores can float in air
Dust can use air as a vehicle containing huge numbers of pathogens
What is vector transmission?
using an organism as an intermediary such as an insect which carries infection
What are the types of vector transmission?
Mechanical (pathogens on vector’s body passively brushed off onto host)
Biological (pathogens are within vector transmission through bite)
What are some vector organisms?
Fleas
Ticks
flies
mosquitos
Do pathogens use vector to replicate?
Some pathogens multiply in vector and arrive at new host lin larger numbers making establishment of infection more likely (less virulent pathogens still establish infection as a result)
What are zoonotic disease?
diseases that require an animal intermediary.
How are zoonotic diseases typically transferred?
Usually through direct contact with humans but can be through indirect contact as well as is the case with waste material of litter box, fur, feathers, infected materials, etc
It can also be transmitted by vectors from animals to humans
What are 3 methods to control transmission of diseases?
Isolation
Quarantine
Vector control
How is isolation typically carried out?
Prevent infected individuals from contact with general population
7 categories of isolation
Patients usually are isolated in hospital
What are the limitations of isolation?
Don’t always know when individual is infected such as
How is quarantine carried out?
Separate those exposed from the population
Quarantine should last as long as incubation period of disease
Once symptoms subside quarantine is lifted
What are the limitations of quarantine?
Very difficult to enforce.
How is vector control carried out?
Killing vectors or using repellants
Mosquito nets
What is the difference between vector and vehicle transmission?
Vector transmission is generally living organism
Vehicle is non-living
Difference between indirect transmission and vehicle transmission:
Time between pathogen landing on intermediate item and it being transmitted. Sometimes categories overlap
What factors affect disease transmission?
Age
Gender
Lifestyle
Occupation
Emotional state
Climate
How does age affect disease transmission?
Disease levels tend to increase with age
How does gender affect disease transmission?
Some more prevalent in one gender than others
How does lifestyle affect disease transmission?
poor nutrition can decrease immuno-competence in host
How does occupation affect disease transmission?
More infections in health care workers
How does emotional state affect disease transmission?
vulnerable emotional state can decrease immune competence in host
How does climate affect disease transmission?
Greater incidence of respiratory illness in colder climates
What is immunocompetence?
Ability of host to mount defence
What happens if host defences are compromised?
Potential for infectious diseases increases
Which group of people are more vulnerable to infections?
People with AIDS or genetic insufficiency diseases
People doing chemo
Surgical transplant and burn patients
Premature newborns
Elderly
Patients on artificial ventilators with cannulas and catheters
What is neutropenia?
Lower neutrophil numbers in blood.
What are neutrophils?
Form of primary phagocytic defence and important component of innate immune system
What are the most common causes of profound neutropenia?
Administration of cytotoxic chemotherapy
Cancer of other diseases with damaged bone marrow
Congenital disorders with poor bone marrow function
Viral infections
Autoimmune disorders that destroy bone marrow cells
Overwhelming infections that use neutrophils faster than they can be made
What kind of infections take advantage of neutropenia?
Bacterial and fungal infections
Often associated with surgical procedures and catheterisation
Why are transplant recipients immunocompromised?
Immunity is lowered to prevent rejection of the organ.
How are infections treated in organ transplat patients?
Broad spectrum antibiotics
Why are burn victims more immunocompromised?
Loss of large areas of primary physical barrier results in greater chance of infection
What bacteria is most problematic for burn patients?
Pseudomonas aeruginosa
Where can opportunistic pathogens arise from?
Normal flora in our bodies
How can opportunistic infections arise?
Movement of opportunistic organisms from one area to another where It can be pathogenic as is the case with UTIs and in cases where flora is compromised by antibiotics
What are nosocomial infections?
hospital infections and are usually associated with intravenous applications
What must hospitals consider regarding nosocomial infections?
Source of infection
Mode of transmission
Susceptibility of patient to infection
Prevention and control
What are the most common sites of the sites of nosocomial infections?
Urinary tract
Respiratory tract
Surgical wounds
What are the most common sources of infections within hospital environment?
Other patients
Hospital staff
Visitors
Unsanitary conditions
Water supplies
Respiratory equipment
Catheters
What are the most common pathogens in nosocomial infections?
E. Coli
Enterococcus species
Staph (+MRSA and VRSA)
Clostridium difficile
Pseudomonas aeruginosa
Many are antibiotic resistant
What are the measures put in place to prevent spread of disease in hospitals?
PPE
Washing hands with antiseptic before and after
Cleaning spills of blood or contaminated fluids
What must hospital programs address regarding nosocomial infections?
Surveillance of nosocomial infections
On-site microbiology lab and standard isolation procedures
Standardised procedures for use of catheters and hospital equipment
Proper decontamination and sanitary procedures
Mandatory nosocomial-disease education programs
Infection-control specialist on staff
What is the difference between incidence and prevalence?
Incidence is the number of new cases
Prevalence is the total number of people infected within a specific population at any given times
(Prevalence is always a larger number because some people will not be newly infected at that given time)
What is the difference between morbidity and mortality?
Morbidity refers to the number of individuals affected by the disease
Mortality is the number of deaths
What is the morbidity rate?
Number of people affected during a set period divided by total population
What is mortality rate?
Number of people died due to specific disease during a set period of time divided by total population
How do epidemiological studies classify diseases?
Sporadic (occurring in random manner)
Endemic (disease constantly in population in low numbers)
Epidemic (incidence of disease suddenly higher than expected morbidity and mortality rates may increase and could eventually become a worldwide problem)
Pandemic (worldwide epidemic)
What is a common source epidemic?
Arises from contact with contaminated substance that affects large number of people and subsides quickly when contamination dealt with (eg. listeria in rockmelon)
What is a propagated epidemic?
Epidemic that is amplified by person to person contact and remains in population for a long time and is more difficult to deal with that common source outbreak
What is herd immunology?
When majority of population is immune there are few potential hosts and disease essentially disappears.
(This is why vaccines are so effective)
What are notifiable diseases?
Diseases that must be reported to the health department of local and state governments.
Why are urinary nosocomial infections most common?
Due to catheters
What is the aetiology of a disease?
Cause of a disease
How can a disease be proven to be a disease?
How can a microorganism be said to cause a disease?
Koch’s postulates
What happens with cultures that cant be grown in pure culture?
Syphilis (treponema pallidum)
Mycobacterium leprae (leprosy)
Viruses and rickettsial organisms
What are the 5 stages of a disease?
Incubation period (no signs or symptoms)
Prodromal period (vague general symptoms)
Illness (most severe signs and symptoms)
Decline (declining signs and symptoms
Convalescence (no signs and symptoms)
How long is the incubation?
Incubation period varies with virulence of pathogen
What is a possible problem that could arise after decline?
Secondary infections
What are some non-communicable diseases?
CVD
Stroke
diabetes
etc
What is the difference between communicable and contagious?
Communicable refers to diseases that can potentially be transmitted and if they are easily spread they are said to be contagious
What are the 4 categories of disease duration?
Acute (develops quickly lasts short time)
Chronic (develops slowly lasts long tim)
Sub-acute (insidious onset (6 - 12 months) almost always fatal
Latent (remains in host after symptoms disappear can come back years later)
What does duration of disease depend on?
Overall health of the host
What are persistent bacterial infections?
Pathogenic bacteria capable of maintaining infections in hosts even in presence of inflammatory specific antimicrobial mechanisms and a good immune response.
How are persistent bacterial infections treated?
Specific anti-microbial therapy
What is the scope of an infection?
scope is whether infection is localized (contained/walled off)
Systemic (moved away from starting point)
What is bacteraemia?
Bacteria in blood
What is septicaemia?
Bacteria growing in blood
What is toxaemia?
Toxins in blood
What is viraemia?
Viruses in blood
What are the 3 types of infection?
Primary (initial infection has acute onset of symptoms)
Subclinical (No symptoms visible and are carriers)
Secondary (People weakened from primary infection and ill again)
What is toxic shock?
Massive leakage of plasma from circulatory system causing massive drop in BP.
What causes toxic shock?
Neutrophils come in contact with M proteins on bacterial surface
What percentage of people that are affected by toxic shock die?
It is fatal for 30 - 70% of patients
What is sepsis?
Presence of pathogen/toxin in blood
What are the 2 forms of sepsis?
severe and acute
What is severe sepsis?
Sytemic inflammation and organ dysfunction
Causes abnormal temperature, HR, Respiratory rate, and WBC count
Elevated number of liver enzymes
Kills slowly over period of weeks with minimal tissue inflammation or damage
What is acute septic shock?
Sudden onset causes death in 24-48 hours
Widespread tissue inflammation and cell damage
