Finding Patient Zero Midterm #1

CPH:2230

patient zero

the first person identified with a disease resulting in an outbreak

asymptomatic carriers, multiple introductions, time lag

reasons why patient zero identification is not always correct or possible

index case

the first person identified in a community or household with a disease in an outbreak whose symptoms bring the disease to the attention of health investigators (first-documented, less stigma)

family cluster

family members/cases associated with the index case

blame, cover-up, generation of alternate theories

what risk of false assumption of index case can mean

primary case

initial person in a SPECIFIC location to be infested, helpful in creating timeline

crossover/spillover case

first person to contract zoonotic disease

reasons why young children have strong potential to index cases of disease

variable health practices, closer proximity to other children, weaker immune systems

asymptomatic carrier

an individuals who carries and transmits disease without showing symptoms (its difficult to determine why some are or are not asymptomatic)

typhoid

a bacterial infection caused by salmonella typhi; mary mallon was able to spread it really easy because she was a private cook

pest houses

used for the quarantine and treatment if infectious diseases such as small pox, cholera, tuberculosis, and typhoid

zoonotic diseases/zoonoses

diseases that are transmitted from animals to people; even with good PPE practices, there is still a risk of transmission

75%

percentage of new infections and emerging diseases in the last 10 years that have originated from animals

more than 90%

percentage of U.S. producers that are aware of at least two zoonotic diseases affecting their livestock

200

number of different zoonoses estimated by WHO

60%

percentage of all global human diseases ever originated from animals

increase in zoonotic diseases are associated with…

larger area of land dedicated to intensive agriculture, growing human population, changes in climate, lack of biodiversity, travel/shipping/globalization

pathogen

an organism that has the potential to cause infectious diseases in its host

reservoir host aka pathogen habitat

a host in the natural world that is the source of an infection or sustaining a pathogen; does not tend to develop infection/clinical signs

human host

humans can serve both as the individual being infected with the pathogen, or as a host serving as a source of infection

zoonotic vector

an organism that transmits a disease or parasite from one animal or plant to another (typically a biting insect)

parasite

disease causing organism that lives on or in an animal host including humans in a harmful manner (parasitic zoonoses are called neglected parasitic zoonoses)

direct contact

immediate, directly on the body; either skin contact or mucus membrane contact

indirect contact

either airborne or fecal-oral transmission

airborne transmission

infectious agents spread by tiny droplets of spray directly into the eyes, nose, or mouth during sneezing, coughing, spitting, or talking; can remain in the air for a prolonged period of time

fecal-oral transmission

ingestion of contaminated feces

airborne versus droplet

remain in air for prolonged period of time versus in the air for a short distance/period of time

fomite

an inanimate object or surface contaminated with an infectious agent; had previous contact with infected person’s body/fluids; can be ingested

viral and bacteria survival times can vary based on

pathogen type, temp, humidity, presence of disinfectants, UV light; bacteria lasts longer

barrier immunity

nasal turbinates, skin, stomach acidity, basically any anatomical intervention or PPE preventing pathogens from entering the body

innate immunity

upper airway & lungs have immune cells that respond to threats like unknown pathogens destroying anything foreign

adaptive immunity

antigens specific to pathogens that bind to proteins on pathogens that make them easier to kill; this is what a vaccine provides; for antibodies to form naturally

skin as barrier immunity

acts as physical barrier, chemical defense, microbiome, & wound healing

parasites (in context of barrier immunity and skin)

many of which can enter through intact skin (in comparison with bacteria or viruses which threaten the skin barrier if the skin is punctured or wounded)

hills causal criteria

temporality, strength of association, biological plausibility, dose/response, consistency

temporality

exposure needs to precede effect or disease; is the ONLY absolutely essential criteria

strength of association

size of association or relationship as measured by statistical tests; the stronger the associatioon, the more likely “A” is causing “B”

biological plasuibility

theoretical basis for positing an association between an exposure and a disease; does it make sense?

dose response gradient

an increasing amount of exposure increases risk of outcome/disease; if its present, there is strong evidence for causality, but its absence doesn’t rule it out; THRESHOLD RELATIONSHIP aka need a certain amount of exposure before disease develops and risk increases

consistency

the association is consistent when results are replicated across multiple studies; if the relationship was causal, we would expect to find it to be reliable

randomized control/clinical trials (rcts)

the golden standard of studies; randomly assigns participants into an experimental or control group; the only expected difference is the outcome variable being studied

cohort study

a group of individuals/participants followed over a set period of time (days to years) in order to gather information about exposures while also monitoring for development of chosen health outcome

cross sectional study

captures exposures and health outcomes at the same point in time; only a snapshot of the population

temporality (css)

the hill’s criteria missing from a cross sectional study compared to a cohort or randomized control trial

kochs postulates

a series of four generalized principles linking microorganisms to specific diseases

1) the microorganism must be abundant in diseased organisms

2) the microorganism must be isolated from a diseased organism and grown in pure culture

3) the cultured microorganism could cause disease when introduced into a healthy organism

4) the microorganism must be re-isolated from the inoculated diseased experimental host and identified as being identical to the original specific causative agent

kochs postulates may not apply to the 21st century because of…

advancements in microbiology, ethical constraints, & antibiotic resistance

R0

reproductive number referring to the number of new or secondary cases of infectious disease that an existing case can generate on average in a susceptible population; spreadability of a pathogen; an estimate not a rate or proportion

if R0>1

than the infection will spread exponentially leading to an epidemic

if R0<1

the infection will spread slowly and eventually die out

R0=1

the disease will remain endemic/stable with each infected person going on to infect another person

case fatality rate

number of people with the disease who have died from it divided by total number of confirmed cases

Why do most fatal disease have low R0 and non fatal have high R0

this is because high mortality rates and isolation can reduce spread because they are so fatal; conversely, non-fatal diseases can spread more easily as they do not lead to immediate death, allowing for greater transmission among the population

High R0 and low mortality rate

think seasonal flu which spreads easily but typically results in few deaths

Low R0 and high mortality rate

think Ebola which requires close contact to spread but has a high case fatality rate

factors influencing R0

infectious period, mode of transmission, contact rate, proportion of susceptible people

Airborne diseases tend to have a higher R0 because

virus particles in the air can travel far or stay and land on surfaces; conversely STIs and disease requiring direct transmission have a lower R0

latent period

is the time between infection and when an individual becomes infectious to others

incubation period

is the time between infection and the onset of symptoms

infectious period

is the timeframe during which an infected individual can transmit the infection to others; could be an asymptomatic carrier

symptomatic period

is the duration in which an individual experiences symptoms of an infection and is often associated with being contagious

R0 formula

transmissibility x average rate of contact between susceptible and infected individuals x duration of infectiousness

Re

effective reproduction number; decreases as more people become immune through infection, recovery, or vaccination; = R0 x (1-Pi)

herd immunity

occurs when a large enough proportion of a population becomes immune making spread from person to person being unlikely, providing protection for those who are not immune; directly proportional to R0

S-I-R model

model used to estimated R0 combining susceptible population, those infected, and those removed/recovered

smallpox

serious infectious disease caused by the variola virus with a proportion of 3/10 people having the disease dying; R0= 3.5-6.0

variolation/innoculation

the method first used to immunize an individual against small pox using material from a patient like a smallpox scab rubbed onto a cut in the skin; between 1-2% of those variolated with smallpox died compared to the natural mortality of 30% for small pox

1×10^91

number of viruses existing in the ocean insinuating that viruses outnumber everything else on our planet

8%

percentage of genome that is made up of viruses that become trapped in host cells

hendra virus

a paramyoxovirus and a henipavirus genus originally found in horses due to bat urine contaminating feed and water; spread to humans through direct contact with body fluids

Bats were targeted and thought to be the host of Hendra because…

its easy for them to travel/ have a large host range and they are mammals so they have a mammalian preference for paramyxoviruses like Hendra; they are also considered a common reservoir host because they are closer in physiology to humans rather than birds

Bat carers had been handling bats yet were not infected with Hendra because…

they need horse as intermediate host to develop virulence (infectionality) to people

amplifying host

species that do not serve as a reservoir for a pathogen but facilitate its replication and transmission leading to increase in prevalence and intensity of the disease

Hendra incubation period

5-21 days for humans & 8-16 days for horses

ribavarin

antiviral drug that may decrease duration and severity/replication of Hendra but clinical usefulness is uncertain

Nipah virus

Hendra’s closely related cousin that originated in Malaysia; pigs are the amplifying host; 4 more heniparviuses were detected in a four year period due to economic development, displacement of bats homes and migration pattern changes due to climate change

Ebola virus

a spaghetti/filamental shaped virus that attacks white blood cells with symptoms appearing 2-21 days after exposure causing complete depletion of hydration; people who recover have antibodies that last for 10 years’ spread through bodily fluids

ring vaccination strategy

a targeted approach where individuals in close contact with a confirmed case are vaccinated to prevent further spread

vaccine hesitancy and distrust, limited access in remote areas, often require freezing/refrigeration

barriers to ebola vaccine being broadly used

spanish influenza (H1N1)

spread during WW1 with 1/3 (500 mil) of the world’s population became infected; case fatality rate of 2-5%; spread from camp funston due to deployment of soldiers globally, lack of hygiene resources, and close proximity to other soldiers in camps; death toll of 50-100 million; called the spanish influenza because spain was the only neutral freely press reporting party'; R0 of 2-3

influenza A

most pathogenic found in birds and mammals; can ALSO seasonly impact humans

influenza b & c

mostly found in humans and are responsible for seasonal infections

influenza d

found in cattle and pigs

hemagglutinin and neuraminidase

surface glycoproteins that make subtypes of influenza a subtypes

endemic

the constant presence and or usual prevalence of a disease in a population within a geographic area (constant an predictable) think seasonal flu

outbreak

a sudden & unexpected increase in the number of cases above the usual baseline in a defined area and time (localized and sudden) think cluster of foodborne illness

epidemic

a sudden increase in number of cases of a disease above what is normally expected in a large population/region (regional and rapid) think ebola outbreak in west africa

pandemic

an epidemic that has spread over several countries or continents (global and uncontrolled) think COVID or spanish flu

spanish flu had high mortality in a mid age population because…

climate and changes in reservoirs, soldiers in overcrowded medical camps, malnourishment/poor hygiene, influenza strain

cytokine storm

a self-amplifying cycle of immune destruction/over-exaggeration of body’s immune response

avian influenza

type A virus spread amongst birds and has the potential to mutate and adapt increasing risk of transmission to humans; highly virulent

influenza family

part of orthomyxoviridae family

genetic reassortment

the process by which a new virus is created from the mixing and matching of genetic material from two or more different viruses (creates a new strain) at a faster frequency and rate

Influenza A is the most pathogenic because…

we know it has more host/susceptible species

HA & NA are

antigens that are recognized by the immune system to produce antibodies

H1N1

spanish flu

H3N2

seasonal flue linked to higher hospitalization

H5N1

majority of human and poultry cases first identified in 1959; human cases from direct animal host contact, so far no sustained person-person transmission (1/2 most common types of avian influenza)

H7N9

primarily infects domestic poultry identified in China in 2013(1/2 most common types of avian influenza)

antigenic shift

point mutations, typically in H & N proteins creating seasonal flu variations (baby step)

antigenic drift

genetic reassortment, avian influenza into human circulating virus, brand new virus strain with new subtypes that can lead to pandemics (large jump)