15. Epidemiology of Infection Flashcards
Distinguish between incidence and prevalence.
Distinguish between infection and disease.
Distinguish between endemic, outbreak, epidemic, pandemic and herd immunity.
Incidence: number of cases during a particular period (= risk of contracting the disease). Prevalence: number of cases at a particular time (= how widespread disease is).
Infection: pathogen entry into body, then multiplication. Disease: disruption of body systems as a result of infection.
Endemic: infection constantly present at particular level, although may be cyclic. OUtbreak: localised increase in incidence of disease. Epidemic: unusual increase in case numbers within a community usually much higher than endemic level, usually short term. Pandemic: epidemic involving several continents. Herd immunity: when majority of population immune to an agent
List some diseases notifiable under the public health control of disease act.
What factors affect infection spread?
What factors affect how easily infection spreads?
Small pox, plague, rabies, yellow fever, mumps, cholera, leprosy, malaria
Pathogen (bacteria, virus, parasite, fungi). Host (definitive host - sexual reprod. intermediate host - asexual reprod.) Environmental (climate, alterations due to man).
Ability to survive and find alturnative host, shedding capacity, infectivity, virulence, pathogenicity, ability to evade immune response.
Give some examples of how pathogens can survive outside the host.
Give examples of shedding.
Intermt of infectivity, what is ID50?
Resistant to drying and UV - Enterovirus. Water - Legionella. Spore formation, lie dormant in soil - Clostridium tetanii spp.
Respiratory (influenza, measles). Skin-contact (herpes simplex). Faecal-oral (hep A). Body fluids/blood/sexual (HIV, hep B, syphilis)
Number of pathogen required to infect 50% of a specified population of susceptible hosts in controlled environmental conditions. E.g. E.coli = 106 - 108
Define: virulence. Give an example of a pathogen with high and low virulence.
What is ID50?
Define pathogenicity.
List some characteristics of the host that play a key role in susceptibility to infection and disease.
The severity of disease caused by a pathogen. Highly virulent e.g. rabies. Low virulence e.g. human herpes virus 6
Individual dose of pathogen which will kill 50% of a specified population of susceptible hosts under controlled condition.
Ability of a pathogen of known virulence to produce disease in a range of hosts under a range of environmental conditions.
Spp, age, sex, ethnic group, occupation and economic status, nutrition, state of immunity
List some environmental factors affecting infection spread.
What are the 3 carrier states?
What is the vertical route of infection? Give examples.
Climate (distribution and population size of vectors e.g. Monsoon and Aedes mosquito). Water supply and sanitation. Change of environment by man (deforestation etc.) Travel.
Incubatory carrier, convalsecent carrier (diarrhoeal illness), chronic carrier (HIV, STIs etc.)
Mother to child: in utero via mother’s blood crossing placenta e.g. rubella, congenital syphilis, or shortly before/during delivery e.g. herpes simplex, hep B
What are the 2 types of horizontal transmission?
List ways in which horizontal infection may occur.
Skin-to-skin transfer usually occurs through abrasions in epidermis. Give some examples.
Direct (sexual, droplet, contact), indirect (vehicle, vector, airbourne)
Direct contact (skin/bodily fluid (blood/saliva/semen)), aerosol transmission (respiratory spread), faecal-oral spread, fomites (inanimate objects), insect/animal vectors, nosocomial transmission (hospital).
Herpes virus. Impetigo (caused by group A strep)
Describe rabies.
How might infection via blood occur?
How is ebola transmitted?
What is a risk of transplant associated infections?
Saliva of infected animal can spread. Virus enters peripheral nerves via bite and spreads to CNS. Alters behaviour via encephalitis (fear of water, agression, violence, promotes own spread)
Blood transfusion/other blood products. Needle sharing. E.g. hep B, HIV
All body fluids: Blood, urine, semen, sweat, faeces, vomit, vaginal secretions
Reactivation of previous dormant infections. Screen pt/donor first!
How do STIs gain access? Give examples.
What does respiratory spread depend on?
How is faecal-oral spread acheived?
How is zoonotic transmission acheived?
Genital tract, oropharyngeal carriage spread. Rectal carriage. E.g. Gonorrhea, syphilis, chlamydia, HIV, shigella
Amount of infective discharge. Resistance to drying/inactivation by UV. Size of aerosol droplets. E.g. measles, chickenpox, MERS
Direct, finger to mouth, “night soil” fertiliser, faecal contamination of food/water. E.g. salmonella, shigella, hep A
Spread from animals, natural reservoirs in animal populations, contact with meat, bodily fluids, milk. E.g. rabies, brucellosis, congo fever
How are vector-bourne diseases transmitted?
What are fomites?
What are nosocomial infections?
By arthropods. Acquire infection by feeding on infected human, passed onto next human when take next blood meal. E.g. lyme disease, malaria, zika, dengue
Inanimate object which can transmit infection.
Hospital acquired: UTIs, wound/skin/soft tissue infections, respiratory tract infections.
How is infection spread prevented?
How can hospital infections be minimised?
Prophylaxis: vaccination - herd immunity (childhood and occupational immunisation, travel vaccines), contact precautions (mosquito nets, DEET).
Self isolation: don’t go to work if sick.
Occupational health monitoring: HIV viral load in those performing exposure prone proceedures. Guidance on returning to work with contagious infections.
Isolating patients with resistant organisms. Handwashing between pts. PPE (gown/gloves/masks/full PPE)
