Disease Detectives B/C

[UTF-8 U+6211 U+662F]

I feel a little lazy... Explain the difference between various types of transmission.

[Knyte_Xjn]

I feel a little lazy... Explain the difference between various types of transmission.

Attempt (Click to Show Hidden Text)

The two overarching types of transmission are direct, in which an infectious agent is directly transferred from a reservoir to a susceptible host, and indirect, in which an infectious agent is transferred from a reservoir to a susceptible host by an intermediary. Direct transmission is further divided into direct contact, characterized by skin-to-skin contact, and droplet spread, typically in the form of short-range aerosols produced by sneezing or coughing. Indirect transmission is further divided into airborne transmission, in which infectious agents are carried by dust or droplet nuclei in the air, vehicular transmission, in which an item or inanimate object that provides an environment capable of sustaining a pathogen, and vectorborne transmission, in which a biological organism transmits an infectious agent through mechanical means, often facilitating its growth.

[UTF-8 U+6211 U+662F]

I feel a little lazy... Explain the difference between various types of transmission.

Attempt (Click to Show Hidden Text)

The two overarching types of transmission are direct, in which an infectious agent is directly transferred from a reservoir to a susceptible host, and indirect, in which an infectious agent is transferred from a reservoir to a susceptible host by an intermediary. Direct transmission is further divided into direct contact, characterized by skin-to-skin contact, and droplet spread, typically in the form of short-range aerosols produced by sneezing or coughing. Indirect transmission is further divided into airborne transmission, in which infectious agents are carried by dust or droplet nuclei in the air, vehicular transmission, in which an item or inanimate object that provides an environment capable of sustaining a pathogen, and vectorborne transmission, in which a biological organism transmits an infectious agent through mechanical means, often facilitating its growth.

Yep, your turn

[Knyte_Xjn]

I feel a little lazy... Explain the difference between various types of transmission.

Attempt (Click to Show Hidden Text)

The two overarching types of transmission are direct, in which an infectious agent is directly transferred from a reservoir to a susceptible host, and indirect, in which an infectious agent is transferred from a reservoir to a susceptible host by an intermediary. Direct transmission is further divided into direct contact, characterized by skin-to-skin contact, and droplet spread, typically in the form of short-range aerosols produced by sneezing or coughing. Indirect transmission is further divided into airborne transmission, in which infectious agents are carried by dust or droplet nuclei in the air, vehicular transmission, in which an item or inanimate object that provides an environment capable of sustaining a pathogen, and vectorborne transmission, in which a biological organism transmits an infectious agent through mechanical means, often facilitating its growth.

Yep, your turn

Suppose that you are designing a test to screen every individual in the United States aged 13-99 for the Bubonic plague.
(a) What pathogen causes the Bubonic plague, and what type of agent is it?
(b) What characteristics should a test of such large extent have? (Hint: mention statistical measures such as specificity)
(c) Why are these characteristics essential, and what adverse results do they serve to prevent? (Hint: include social impacts)
(d) Suppose that an individual tests positive for the Bubonic plague. Provide a way that you can follow up on the test results to ensure that the first test wasn't a false positive.
(e) Assume that your test does have the characteristics named in part B. Is it necessary to follow up on negative tests? If so, provide a way that you can follow up to ensure that the first test wasn't a false negative.
(f) Explain the difference between sensitivity and positive predictive value. How do they pertain to this test?
(g) Explain the difference between specificity and negative predictive value. How do they pertain to this test?

[Birdmusic]

Suppose that you are designing a test to screen every individual in the United States aged 13-99 for the Bubonic plague.
(a) What pathogen causes the Bubonic plague, and what type of agent is it?
(b) What characteristics should a test of such large extent have? (Hint: mention statistical measures such as specificity)
(c) Why are these characteristics essential, and what adverse results do they serve to prevent? (Hint: include social impacts)
(d) Suppose that an individual tests positive for the Bubonic plague. Provide a way that you can follow up on the test results to ensure that the first test wasn't a false positive.
(e) Assume that your test does have the characteristics named in part B. Is it necessary to follow up on negative tests? If so, provide a way that you can follow up to ensure that the first test wasn't a false negative.
(f) Explain the difference between sensitivity and positive predictive value. How do they pertain to this test?
(g) Explain the difference between specificity and negative predictive value. How do they pertain to this test?

Answer? (Click to Show Hidden Text)

All answers assuming you want to implement this test right now, not during an outbreak.
a) It is caused by Yersinia pestis, a bacterium.
b) It should have high specificity and sensitivity ideally, but that is hard to achieve. If there was an active outbreak, sensitivity would be better, but in normal circumstances (ie right now), specificity is better to avoid causing panic over false positives. (Bubonic plague is really rare in the US, causing the test to be more likely to find more false positives than true positives, so higher sensitivity can help avoid that.) High PPV and NPV are also ideal but hard to achieve at the same time, and NPV would be better during an outbreak because less false negatives and PPV better for normal circumstances because less false positives.
c) Specificity prevents false positives, which can cause panic among people and lead to unnecessary antibiotic use, promoting antibiotic resistance in other bacteria.
d) You can take a sample of lymph node fluid and culture it to see if there is any bubonic plague. Alternatively, you can put them in a quarantined area for a week since bubonic plague has a short incubation period.
e) No, that would be impossible because most tests would be true negatives. There are very few cases of actual bubonic plague in the US every year, so following up on every negative test would basically get you nowhere.
f) Sensitivity is the number of people with the disease that are categorized as positive by the test, so higher sensitivity is less false negatives. This is useful during the beginning of outbreaks to find all possible cases, and would be useful during an outbreak of bubonic plague. Positive predictive value is the number of true positive results over all positive results. A higher PPV means less false positives, which is useful for rare diseases and ones that are likely to cause public panic when there isn't an outbreak, like bubonic plague.
g) Specificity is the number of people without the disease that are tested negative. A higher specificity means less false positives. It is useful for the same reason as PPV. NPV is the number of true negatives over all negatives, which has similar benefits to sensitivity.

[Knyte_Xjn]

Suppose that you are designing a test to screen every individual in the United States aged 13-99 for the Bubonic plague.
(a) What pathogen causes the Bubonic plague, and what type of agent is it?
(b) What characteristics should a test of such large extent have? (Hint: mention statistical measures such as specificity)
(c) Why are these characteristics essential, and what adverse results do they serve to prevent? (Hint: include social impacts)
(d) Suppose that an individual tests positive for the Bubonic plague. Provide a way that you can follow up on the test results to ensure that the first test wasn't a false positive.
(e) Assume that your test does have the characteristics named in part B. Is it necessary to follow up on negative tests? If so, provide a way that you can follow up to ensure that the first test wasn't a false negative.
(f) Explain the difference between sensitivity and positive predictive value. How do they pertain to this test?
(g) Explain the difference between specificity and negative predictive value. How do they pertain to this test?

Answer? (Click to Show Hidden Text)

All answers assuming you want to implement this test right now, not during an outbreak.
a) It is caused by Yersinia pestis, a bacterium.
b) It should have high specificity and sensitivity ideally, but that is hard to achieve. If there was an active outbreak, sensitivity would be better, but in normal circumstances (ie right now), specificity is better to avoid causing panic over false positives. (Bubonic plague is really rare in the US, causing the test to be more likely to find more false positives than true positives, so higher sensitivity can help avoid that.) High PPV and NPV are also ideal but hard to achieve at the same time, and NPV would be better during an outbreak because less false negatives and PPV better for normal circumstances because less false positives.
c) Specificity prevents false positives, which can cause panic among people and lead to unnecessary antibiotic use, promoting antibiotic resistance in other bacteria.
d) You can take a sample of lymph node fluid and culture it to see if there is any bubonic plague. Alternatively, you can put them in a quarantined area for a week since bubonic plague has a short incubation period.
e) No, that would be impossible because most tests would be true negatives. There are very few cases of actual bubonic plague in the US every year, so following up on every negative test would basically get you nowhere.
f) Sensitivity is the number of people with the disease that are categorized as positive by the test, so higher sensitivity is less false negatives. This is useful during the beginning of outbreaks to find all possible cases, and would be useful during an outbreak of bubonic plague. Positive predictive value is the number of true positive results over all positive results. A higher PPV means less false positives, which is useful for rare diseases and ones that are likely to cause public panic when there isn't an outbreak, like bubonic plague.
g) Specificity is the number of people without the disease that are tested negative. A higher specificity means less false positives. It is useful for the same reason as PPV. NPV is the number of true negatives over all negatives, which has similar benefits to sensitivity.

Great answers! Your turn

[Birdmusic]

What is the RR (risk ratio) for the following scenario?
...........Disease | No disease
Exposed 10 .....|....... 5
Not Exposed 3 .|........ 18

What does it mean? (ie 2 times more/less likely to get the disease if exposed)
What study type is RR used in? What about OR (odds ratio)?

[UTF-8 U+6211 U+662F]

What is the RR (risk ratio) for the following scenario?
...........Disease | No disease
Exposed 10 .....|....... 5
Not Exposed 3 .|........ 18

What does it mean? (ie 2 times more/less likely to get the disease if exposed)
What study type is RR used in? What about OR (odds ratio)?

Click to Show Answer

RR=4.67

Exposed people are 4.67 times as likely to get the disease as unexposed people.

Relative risk can be used in a cohort study.

Relative risk cannot be used in a case-control study, so odds ratio is used.

[Birdmusic]

What is the RR (risk ratio) for the following scenario?
...........Disease | No disease
Exposed 10 .....|....... 5
Not Exposed 3 .|........ 18

What does it mean? (ie 2 times more/less likely to get the disease if exposed)
What study type is RR used in? What about OR (odds ratio)?

Click to Show Answer

RR=4.67

Exposed people are 4.67 times as likely to get the disease as unexposed people.

Relative risk can be used in a cohort study.

Relative risk cannot be used in a case-control study, so odds ratio is used.

Looks good, your turn!

[UTF-8 U+6211 U+662F]

What's the difference between incidence and prevalence?