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Micro exam 3 Questions with Solutions
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Micro exam 3EPIDEMIOLOGY - answer
what is puerperual fever? How is it relevant to the history of epidemiology? -
answerpuerperual fever is a bacterial infection of the uterus. By mid 19th century, one
out of eight women died in vienna hospitals following childbirth. Ignaz Semmelweis
observed puerperal fever. Incidence in one section run by medical students was four
times second section run by midwives and midwifery students. A fried of Semmelweis
sustained a scalpel wound during an autopsy, died of symptoms similar to puerperal
fever. Semmelweis reasoned poison that killed his friend was transferred to women in
childbirth by medical students. Before Pasteur, Koch: germ theory of disease. Poison
was probably streptococcus pyogenes. Washing hands with strong disinfectant:
incidence of puerperal fever dropped to one-third previous level.
what is epidemiology? - answerEpidemiology is study of distribution and causes of
disease in populations. Epidemiologists collect, compile data about sources of disease
and risk factors. Design strategies to prevent/predict spread of disease. Expertise in
many disciplines including ecology, microbiology, sociology, statistics, and psychology.
Many daily habits (handwashing, waste disposal) are based on epidemiology
what is the difference between communicable and non-communicable diseases -
answerCommunicable diseases are contagious. Transmitted from one host to another.
ex. measles, colds, influenza. Transmission may be direct ex. kiss or indirect ex.
drinking from a glass used by someone else
Non-communicable diseases do not spread from host to host. Microorganisms most
often arise from individual's normal microbiota or environment (for example, legionella
pneumonphila in water systems of buildings)
what is the attack rate - answerattack rate is a percentage of people who become ill in
population after exposure to infectious agent. Reflects infectious dose and immune
status of population. Usually determined retrospectively.
what is incidence - answerincidence is number of new cases/time/population. Measures
risk of an individual contracting a disease. Usually measured over a short time period.
what is prevalence - answerprevalence is the total number of cases at any time or for a
specific period in a given population. Reflects overall impact of disease on society;
includes old and new cases, as well as duration of disease. Usually measured over
longer period of time, sometimes the entire length of the outbreak
,what is morbidity - answermorbidity is incidence of disease in a population. Contagious
diseases ex. flu often have high morbidity rate: infected individual may transmit to
several others. Asymptomatic individuals excluded.
what is mortality - answermortality is overall death rate in population
what is case-fatality rate - answercase fatality rate is the proportion of people who die
from a specified disease among all individuals diagnosed with the disease over a
certain period fo time. The ebola virus was very feared because of very high case-
fatality rate (50%).
what is an endemic disease - answerendemic disease constantly present in population.
ex. common cold, lyme disease, plague
what is a sporadic disease - answersporadic diseases have a few cases from time to
time
what is an epidemic - answeran epidemic is an unusually large number of cases. Can
be from introduced or endemic disease.
what is an outbreak - answeran outbreak is a group of cases at specific time and
population. ex. 2019 measles outbreak in USA
what is a pandemic - answera pandemic is global ex. AIDS; COVID 19
what is the chain of infection? What are its steps? - answerSpread of infectious disease
follows series of steps called the chain of infection. Knowing the chain for a given
disease allows determination of where the chain can be broken.
Steps:
1. Reservoir of infectious agent
2. portal of exit
3. transmission
4. portal of entry
5. susceptible host
what is the reservoir of infection? Why is it significant? - answerThe reservoir of
infection is the natural habitat of a pathogen. can be In or an animal, human, or in the
environment ex. soil, water, air. Identification of reservoir important in disease control. A
pathogen is often easier to control if humans are the only reservoir. ex. smallpox (easier
to control b/c of vaccine). But this is not always the case ex. gonorrhea, syphillis, AIDS,
others.
what is the difference between symptomatic and asymptomatic infections? -
answerSymptomatic infections provide a clear source of pathogens. Disease may be
,spread before symptoms appear or after they go away. Asymptomatic infections are
harder to identify, carriers may not notice infection, but can spread it to others may lead
to uncontrollable spread ex. Covid 19. This is why testing is very important. In
Asymptomatic infections, Immune system may be responding to pathogen, inhibiting
expression of symptoms. Up to 50% of women infected with Neisseria gonorrhoeae are
asymptomatic, easily transmit it. High percentage of Covid 19 infections are likely
asymptomatic. Potential pathogens may be part of normal microbiota. Many people
carry staphylococcus aureus.
describe the challenges of non-human animal reservoirs of infection - answernon-
human animal reservoirs are difficult to control in wild animal populations. ex. Plague
(spread by fleas), hantavirus (spread by mice), lyme disease (spread by ticks).
Zoonoses (zoonotic disease) are diseases of animals that are transmitted to humans.
More severe in humans because there is no co-evolution toward balanced
pathogenicity. i.e. attenuation of pathogen and increased resistance of host. Basically,
humans have never seen these diseases before, and are therefore at our most
vulnerable.
describe challenges of environmental reservoirs of infection - answerenvironmental
reservoirs are difficult or impossible to eliminate. ex. colostridium, legionella, bacillus
anthracis (anthrax)
what is a portal of entry? what are the different types? - answerA portal of entry is a
body surface or orifice that serves as an entry route for a pathogen. *Respiratory route*:
respiratory pathogens generally cause disease only when inhaled (nose). *Alimentary
route*: Pathogens entering by this routhe (oral) generally cause disease only when of
the intestinal tract. Fecal oral transmission: fecal organisms transported to mouth and
ingested. *Parenteral route*: penetration of the skin. Pathogen usually ends up in
lymphatic system and/ or blood stream. Can be very serious.
what is a portal of exit? what are the different types? - answerPortal of exit is a body
surface or orifice that serves as an exit route for a pathogen.
1. Intestinal tract: shed in feces ex. vibrio cholerae, E. coli, Salmonella, Shigella)
2. Respiratory tract: can exit in droplets of saliva, mucus ex. tuberculosis, pertussis,
influenza, coronavirus
3. Skin: shed on skin cells ex. staphylococcus aureus
4. genital pathogens: semen, vaginal secretions. ex. neisseria gonorrhoeae, HPV
what is the difference between vertical and horizontal transmission? - answerVertical
transmission is pregnant woman to fetus or mother to infant during childbirth or breast
feeding. Horizontal transmission is person to person via air, physical contact, ingestion
of food or water, or vector
what is direct transmission? What are the different types? - answerDirect transmission
involves immediate transfer of infectious agent to portal of entry. One example of direct
, transmission is through direct contact, which includes touch, handshake, kissing, sexual
intercourse. This is easiest when infectious dose is low, such as Shigella. Handwashing
considered single most important measure for preventing spread of infectious disease.
Some pathogens cannot survive in environment, require intimate sexual contact ex. all
STIs. Another example of direct transmission is through droplet transmission, which can
spread respiratory disease when pathogen laden droplets are inhaled after a sneeze,
cough, talking, etc. Droplets generally fall to the ground within a meter. Spread
minimized by covering mouth when sneezing.
what are the different ways in which indirect transmission can occur? - answer1.
airborne
2. vehicle-borne
3. vector borne
describe airborne indirect transmission - answerairborne: respiratory diseases often
transmitted by liquid droplets released while talking, etc. Droplet nuclei (microbes
attached to dried material) remain suspended; inhaled, carry pathogens to lungs. Other
airborne particles include dead skin cells, dust. Crowds increase number of bacteria in
the air. Airborne pathogens are difficult to control. Ventilation systems, negative
pressure, and HEPA filters can help prevent spread in healthcare facilities
describe vehicle-borne indirect transmission - answervehicle borne means transmitted
by objects, food, or water. Fomites are inanimate objects that transmit disease such as
clothing, keyboards, doorknobs, drinking glasses. Food and water can become
contaminated, but they are not considered fomites. Animal products such as meat or
eggs frequently carry disease from animal's intestine. Cross-contamination: transfer of
microbes between foods. Municipal water systems can distribute to large numbers. ex.
Cryptosporidium parvum outbreak in wisconsin in 1993 affected over 400,000 people
describe vector-borne indirect transmission - answerVector borne: a vector is a living
organism that can carry a pathogen. Most often arthropods: mosquitoes, flies, fleas,
lice, ticks. Mechanical vector carries microbe on its body from one location to another.
Biological vector also participates in life cycle of pathogen. ex. Plasmodium (malaria
parasite) multiplies to high numbers of the infectious form of the parasite in the
mosquito. Yersina pestis (plague bacillus) causes blockage in the gut of the flea causing
it to regurgitate its gut contents (i.e. Y. pestis, into the bite wound). *Vector control
important in preventing vector-borne diseases*
what is virulence - answervirulence is ability to cause disease. Factors that allow
pathogen to attach to host cell, avoid immune defenses, damage host, all impact
virulence.
what is infectious dose? - answerinfectious dose is the number of pathogens
introduced; minimum number of pathogens required to produce symptoms. differs with
every pathogen. If few cells enter, immune system may eliminate organism before
symptoms appear.
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