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Public Health > Infectious Diseases > Flashcards

Infectious Diseases Flashcards

1
Q

Definition of epidemiology

A

The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems.

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2
Q

Study

A

Surveillance, observation, hypothesis testing, analytic research, experiments

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3
Q

Distribution

A

By time, place, persons affected
i.e. When, where, who

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4
Q

Determinants

A

Physical, biological, social, cultural, behavioral factors that influence health & distribution of
i.e. How? What?

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5
Q

Specified population

A

’: Specific characteristics e.g. Sex workers
i.e. Who?

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6
Q

Application

A

Aim - to promote, protect, restore health
i.e. So what?

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7
Q

What is an infectious/ communicable disease

A

An illness
due to a specific infectious agent or its toxic products
that arises through transmission of that agent or its products
from an infected person, animal, or reservoir to a susceptible host,
either directly or indirectly through an intermediate plant or host, vector, or the inanimate environment

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8
Q

The epidemiological triad

A

The Epidemiological Triad is a model used to understand the causation of infectious diseases, consisting of three components: the agent, the host, and the environment.

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9
Q

What is the ‘agent’ in the Epidemiological Triad?

A

The agent is the cause of the disease. It can be a microbe, such as bacteria, viruses, fungi, or parasites, or a chemical or physical factor that causes illness or injury.

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10
Q

What is the ‘host’ in the Epidemiological Triad?

A

The host is the organism, usually a human or an animal, that can be affected by the agent. Factors such as immunity, genetic susceptibility, and nutritional status can influence the host’s susceptibility to the agent

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11
Q

What is the ‘environment’ in the Epidemiological Triad?

A

The environment includes all external factors that affect the agent and the opportunity for exposure. This can include physical factors like climate and geography, biological factors like vectors and reservoirs, and social factors like population density and sanitation

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12
Q

How do the components of the Epidemiological Triad interact?

A

The agent, host, and environment interact in a way that determines the occurrence of disease. The agent must be able to infect a susceptible host, and the environment must support the transmission and survival of the agent.

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13
Q

What is different about infectious diseases?

A
  1. The organisms that cause infectious diseases are necessary causes
  2. Certain organisms may cause infection and there may be no evidence of disease for years although the individual may spread the infection
  3. Immunity may be acquired by exposure to certain organism or through immunization with vaccines and this may provide protection against re-infection with the same organism
    4 Source
  4. One can sometimes immediately control predisposing factors but often not
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14
Q

what is the difference between infection and disease?

A

Infection
-Invasion of a host by an agent, with subsequent establishment & multiplication of agent
-May or may not lead to disease

Disease
-A condition of abnormal physiological functioning/ anatomical structure
-Sometimes the host response contributes more to tissue destruction/malfunction than the infectious agent

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15
Q

Two important characteristics used to CLASSIFY infectious diseases

A
  1. The Reservoir of the organism
  2. The Means (or Mode) of transmission
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16
Q

What is the definition of a reservoir according to Giesecke?

A

A reservoir is an ecological niche where a pathogen lives and multiplies.

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17
Q

What is the difference between a reservoir and a source?

A

The source is the actual object, animal, or person from which the infection is acquired, while the reservoir is the natural habitat of the infectious agent.

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18
Q

Can you provide an example of a reservoir?

A

An example is malaria, where humans act as the reservoir and mosquitoes transfer the pathogen from one human to another.

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19
Q

What is the definition of a source according to Giesecke?

A

The source is the actual object, animal, or person from which the infection is acquired.

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20
Q

Can you provide examples of sources of infection?

A

Examples include air vents and water tanks.

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21
Q

type The means of transmission

A
  1. direct transmission i.e. person to person
  2. indirect transmission i.e. by a common vechicle or vector
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22
Q

types of direct transmission

A
  • mucous membrane to mucous membrane
  • across placenta
  • blood
  • skin to skin
  • sneezes or coughs
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23
Q

types of indirect transmission

A
  • food borne
  • water
  • objects
  • vectors (mosquitoes)
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24
Q

definition of prevalence

A

Burden of infection or disease in community

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25
Q

formula to calculate prevalence

A

Prevalence = Incidence x Duration

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26
Q

challenges with prevalence

A

Some infectious diseases have short duration/occurs repeatedly
-Many infectious diseases have a short duration and may occur repeatedly, and thus prevalence is not as important a measure in these instances
-E.g. Diarrhoeal/resp infections (point prevalence may be low but annual incidence high)

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27
Q

When is prevalence useful

A

Some infectious diseases are chronic in nature
-Some infectious agents have a chronic nature, and both incidence and prevalence are important measures with prevalence providing a more accurate measure of risk of infection and the size of the infectious pool
-E.g. Hep B, TB, HIV

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28
Q

definition of incidence

A

Number of new cases over a period of time

Incidence may be decreasing at the same time that prevalence is rising

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29
Q

Why is it important to understand time periods of infection

A

-To monitor and investigate outbreaks
-To know how fast the infection/disease will spread/decrease

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30
Q

definition of incubation period

A

The time between exposure to an infectious agent and the onset of symptoms or signs of infection

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31
Q

variation of incubation period is due to

A

Dose
Route
Rate of replication
Host

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32
Q

what does incubation period allows one to determine

A

-when infection occurred
-who could be a contact, length of quarantine period

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33
Q

Latent period

A

Time period from successful infection until the development of infectiousness

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34
Q

Infectious period

A

Period following infection when infection can be transmitted to another susceptible host

onset of shedding

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35
Q

serial interval

A

For diseases that are spread from person to person the time period between successive generations

Time between the appearance of similar SYMPTOMS in successive generations

If person is infectious before symptoms occur (i.e. latent period shorter than incubation period) the serial interval will be shorter than the incubation period

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36
Q

What follows EXPOSURE to an infectious agent? i.e. what are all the possible outcomes?

A

no foothold
clinical infection
subclinical infection
carriage/ colonisation

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37
Q

what happens after an infection

A

death
immunity
carriage
non- immunity

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38
Q

define infectivity

A

Definition:
The ability of an agent to cause infection in a susceptible host

Example: Hep B very infective; HIV far less so

39
Q

How is infectivity measured in

A

Minimum number of infectious particles required to establish infection
BUT this does not necessarily mean that disease will occur

40
Q

What does infectivity determines

A

extent to which disease will be transmitted
how long patients should be isolated/ quarantined for

41
Q

What is infectivity in the context of person-to-person diseases?

A

Infectivity is measured by the secondary attack rate, which is the proportion of susceptibles who develop infection within the incubation period after exposure to a primary case

42
Q

What is the numerator in the secondary attack rate for measuring infectivity?

A

The numerator is the number of secondary cases (infections) within the incubation period.

43
Q

What is the denominator in the secondary attack rate for measuring infectivity?

A

The denominator is the total number of people in contact with a primary case.

44
Q

Why is it difficult to measure infectivity using the secondary attack rate?

A

It is difficult to measure if there is sub-clinical disease, as these cases may not be detected.

45
Q

What are other names for attack rate or risk?

A

Attack rate or risk is also known as incidence proportion or cumulative incidence

46
Q

What is pathogenicity?

A

Pathogenicity is the ability of a microbial agent to induce disease.

47
Q

How is pathogenicity measured?

A

Pathogenicity is measured by the illness rate, which is the number of people with disease divided by the number of people with infection.

48
Q

What does it mean if a disease has high pathogenicity?

A

If all infections lead to disease, the disease has high pathogenicity, and the illness rate would be 100%.

49
Q

Can you give examples of diseases with high pathogenicity?

A

Smallpox
Measles
Chicken pox
Rhinoviruse

50
Q

What is virulence?

A

Virulence is the severity of disease after infection occur

51
Q

How is virulence measured?

A

Virulence is measured by the case fatality ratio or the proportion of clinical cases that develop severe disease.

52
Q

Can you give an example comparing the virulence of two diseases?

A

Smallpox is far more virulent than rhinoviruses, which cause colds.

53
Q

Why is virulence important in epidemiology?

A

If cases die rapidly, this impacts the infectious pool of patients spreading the infection.

54
Q

Epidemiology of infectious disease include evaluation of

A

-reservoir
- infectivity
- pathogenicity
- virulence

55
Q

What is immunogenicity?

A

Immunogenicity is the ability of an organism to induce specific immunity, i.e., to produce an immune response after infection capable of providing protection against reinfection with the same or similar organism.

56
Q

What aspect of the host does immunogenicity focus on?

A

Immunogenicity looks at the effect of the agent on the host’s immune system.

57
Q

Can you give examples of diseases that induce solid life-long immunity?

A

Examples include Measles and Polio.

58
Q

Can you give an example of a weakly immunogenic organism?

A

Malaria (P. Falciparum) is weakly immunogenic with some protection.

59
Q

Can you give examples of organisms that provoke an immune response that is harmful to the host?

A

Group A streptococci can provoke an immune response that leads to kidney inflammation (glomerulonephritis) or rheumatic heart disease, and TB often shows markers of infection but no immunity.

60
Q

What do reproductive numbers estimate?

A

Reproductive numbers estimate the average number of secondary cases originating from a primary case during their entire infectious period. Also known as R naught (R0).

61
Q

What factors determine the reproductive number?

A

Reproductive numbers are a function of:

-Infectiousness (Secondary Attack Rate)
-Contact pattern
-Duration of infectiousness
-Proportion immune in the population

62
Q

2 types of reproductive number

A
  • basic reproductive number
  • net reproductive number
63
Q

What is the Basic Reproductive Number?

A

The Basic Reproductive Number is “the expected number of secondary cases from a single case introduced into a totally susceptible population.”

64
Q

What is the Net Reproductive Number?

A

The Net Reproductive Number is the reproductive number at a specified time.

65
Q

What is the Basic Reproductive Number?

A

The Basic Reproductive Number is the average number of infections that a single infected individual will cause in a ‘naïve’ population, which means a population that hasn’t seen the pathogen before. It represents the maximum reproductive number when the entire population is susceptible

66
Q

What does the Basic Reproductive Number represent?

A

It represents the average number of persons directly infected by an infectious case during their entire infectious period when they enter a totally susceptible population.

67
Q

How do you interpret the Basic Reproductive Number?

A

If R0 < 1, the disease will eventually disappear.

If R0 = 1, the disease will become endemic.

If R0 > 1, there will be an epidemic.

68
Q

Formula to calculate the reproductive number

A

R0= B* c* D

69
Q

B

A

Probability of transmission in a contact between infected and susceptible individuals

i.e. it is the same as the infectiousness or secondary attack rate

i.e. number of secondary cases divided by number of contacts

70
Q

c

A

Frequency of contacts in the population

Or number of exposures of susceptible persons to infectious partners per unit time

Or probability of contact

Average number of exposures per unit time e.g. average number of people in contact with an infectious person per day

71
Q

D

A

How long an infected person is infectious

Infectiousness of infected person

Unit of time e.g. days

72
Q

What is Herd Immunity?

A

Herd Immunity is the level of immunity required to prevent epidemics. For example, for measles, 94% immunity is required because it has a high R0. Once a certain proportion of people are immune in a community, the likelihood is small that an infected person will encounter a susceptible person to whom they can transmit the infection, assuming there is random mixing.

73
Q

Why is it difficult to achieve complete Herd Immunity?

A

In reality, it is difficult to achieve complete random mixing. Hence, certain pockets in the population may not reach herd immunity, leading to localized outbreaks.

74
Q

How do you calculate the Herd Immunity Threshold (HIT)?

A

HIT = (R0-1)/R0

Or HIT = 1-(1/R0

75
Q

What is an Outbreak?

A

An Outbreak is an increase in the observed number of cases of a disease or health problem compared to the expected number for a given place or among a specific group of people over a particular time period.

76
Q

What is an Upsurge?

A

An Upsurge, also known as an Outbreak, is a localized increase in cases where 2 or more cases are epidemiologically linked.

77
Q

What is a Cluster?

A

A Cluster is a group of cases of disease believed to be greater than expected, associated in time and space.

78
Q

What does it mean for cases to be Epidemiologically Linked?

A

Cases are Epidemiologically Linked when a patient has had contact with one or more persons with the disease, and transmission of the agent by the usual modes of transmission is plausible.

79
Q

What is the outbreak investigation?

A

The outbreak investigation is a systematic process of evaluating data to form hypotheses, followed by collecting additional data to test these hypotheses.

80
Q

Are the steps of an outbreak investigation always conducted in a specific sequence?

A

No, the steps of an outbreak investigation are not necessarily conducted in a specified sequence.

81
Q

Why is quick implementation of control measures paramount during an outbreak?

A

Quick implementation of control measures is crucial to prevent further spread of the disease. Adjustments to these measures should be made based on collecting more and better data.

82
Q

What are the objectives in controlling an outbreak?

A

The objectives include minimizing the number of primary cases and promptly recognizing the outbreak, as well as identifying and controlling the source.

83
Q

How can you minimize the number of secondary cases during an outbreak?

A

Minimizing secondary cases involves identifying cases early and taking action to control the spread of the disease.

84
Q

What is the goal of preventing further episodes of disease during an outbreak?

A

The goal is to identify and eliminate continuing hazards, minimizing their risk to prevent further outbreaks.

85
Q

Challenges in controlling infectious disease

A

-Re-emergence of old diseases – cholera, typhoid
-Changes in environment, agriculture & food-processing, movement of people and goods, behaviors
-Increased density of populations (refugees)
-Increased susceptibility
-Bioterrorism

86
Q

Advances of control of infectious disease

A
  1. Lab techniques, molecular epidemiology – DNA finger printing
  2. Epidemiology
  3. Vaccines
  4. Communication
87
Q

Steps for an outbreak investigation

A
  1. verify the diagnosis
  2. establish the existence of an outbreak
  3. identify and count cases
  4. describe the epidemiology
  5. formulate and test hypothesis
  6. assess local response capacity and address resource gaps
  7. set up control measures
  8. communicate findings
  9. intensify surveillance
88
Q

phases of an epidemic

A
  1. sporadic cases
  2. clusters
  3. main wave
  4. full epidemic
  5. late epidemic
89
Q

What characterizes the introduction phase of an epidemic?

A

The introduction phase begins with the entry of a new pathogen into a susceptible population.

90
Q

Describe the growth phase of an epidemic.

A

The growth phase is marked by a rapid increase in the number of cases as the pathogen spreads within the community

91
Q

What happens during the peak phase of an epidemic?

A

The peak phase represents the highest point of the epidemic curve, where the number of new cases reaches its maximum.

92
Q

How is the decline phase of an epidemic characterized?

A

The decline phase shows a decrease in the number of new cases as interventions and natural immunity begin to reduce transmission.

93
Q

What defines the resolution phase of an epidemic?

A

The resolution phase occurs when the epidemic is considered over, with few or no new cases occurring within the community.

Public Health (16 decks)

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