Disease Detectives B/C

[yang573]

Should I post a less ramble-y question?

[dcrxcode]

This is going to be a bit different, but here's a basic analytical study.

You have been asked to investigate a possible outbreak of cholera in Yorktown. Cholera is caused by the bacterium Vibrio Cholerae. It can be found in contaminated water, and it infects the small intestine. The disease typically manifests itself within 2-3 days of infection, but it can take anywhere from a few hours to 5 days for symptoms to appear. Diarrhea is the most common symptom, and this can be accompanied by vomiting, rapid heart rate, loss of skin elasticity, and other effects of rapid dehydration. If left untreated, severe dehydration can cause shock and death.

Yorktown is a small community composed of 115 people. When you arrive at the scene, the typical sight of people tending their crops has been replaced by a sparse scattering of a select few in the fields. As there aren’t many households in the town, you decide to survey the entire population for cases of cholera, as well as how the residences acquire their dihydrogen oxide. There have been 73 cases of severe diarrhea cholera since December 10th. 45 of those infected reported drawing water from a communal well, while the others said they got their water from a nearby stream. Among those who had not (yet (optimistic aren’t we)) been infected, 35 reported getting their water from the stream, and the rest acquired their water from the well.

• 1.Calculate the relative risk for each water source (please). Round to the nearest hundredth.
  2.Which water source seems to be the source of the outbreak?
  3.How might some of the case-patients have acquired cholera without drinking from the contaminated water source?

Answer (Click to Show Hidden Text)

1. relative risk for communal well: (45/52)/(28/63)=1.95
relative risk for nearby stream: (28/63)/(45/52)=0.51
2. The well seems to be the source of the outbreak since the RR of it is higher at 1.95 compared to the stream.
3. Cholera is generally spread fecal-orally, so it could have been spread through contaminated food as well.

[yang573]

This is going to be a bit different, but here's a basic analytical study.

You have been asked to investigate a possible outbreak of cholera in Yorktown. Cholera is caused by the bacterium Vibrio Cholerae. It can be found in contaminated water, and it infects the small intestine. The disease typically manifests itself within 2-3 days of infection, but it can take anywhere from a few hours to 5 days for symptoms to appear. Diarrhea is the most common symptom, and this can be accompanied by vomiting, rapid heart rate, loss of skin elasticity, and other effects of rapid dehydration. If left untreated, severe dehydration can cause shock and death.

Yorktown is a small community composed of 115 people. When you arrive at the scene, the typical sight of people tending their crops has been replaced by a sparse scattering of a select few in the fields. As there aren’t many households in the town, you decide to survey the entire population for cases of cholera, as well as how the residences acquire their dihydrogen oxide. There have been 73 cases of severe diarrhea cholera since December 10th. 45 of those infected reported drawing water from a communal well, while the others said they got their water from a nearby stream. Among those who had not (yet (optimistic aren’t we)) been infected, 35 reported getting their water from the stream, and the rest acquired their water from the well.

• 1.Calculate the relative risk for each water source (please). Round to the nearest hundredth.
  2.Which water source seems to be the source of the outbreak?
  3.How might some of the case-patients have acquired cholera without drinking from the contaminated water source?

Answer (Click to Show Hidden Text)

1. relative risk for communal well: (45/52)/(28/63)=1.95
relative risk for nearby stream: (28/63)/(45/52)=0.51
2. The well seems to be the source of the outbreak since the RR of it is higher at 1.95 compared to the stream.
3. Cholera is generally spread fecal-orally, so it could have been spread through contaminated food as well.

That is correct. The only thing I would mention is that I believe the well would be considered the source because the RR is greater than 1, not necessarily because the RR is higher than the RR of the stream. In addition, cholera may have also been transmitted when people cared for the sick, and if children played in contaminated water (although the latter is more of an issue in developing countries).

[dcrxcode]

This is going to be a bit different, but here's a basic analytical study.

You have been asked to investigate a possible outbreak of cholera in Yorktown. Cholera is caused by the bacterium Vibrio Cholerae. It can be found in contaminated water, and it infects the small intestine. The disease typically manifests itself within 2-3 days of infection, but it can take anywhere from a few hours to 5 days for symptoms to appear. Diarrhea is the most common symptom, and this can be accompanied by vomiting, rapid heart rate, loss of skin elasticity, and other effects of rapid dehydration. If left untreated, severe dehydration can cause shock and death.

Yorktown is a small community composed of 115 people. When you arrive at the scene, the typical sight of people tending their crops has been replaced by a sparse scattering of a select few in the fields. As there aren’t many households in the town, you decide to survey the entire population for cases of cholera, as well as how the residences acquire their dihydrogen oxide. There have been 73 cases of severe diarrhea cholera since December 10th. 45 of those infected reported drawing water from a communal well, while the others said they got their water from a nearby stream. Among those who had not (yet (optimistic aren’t we)) been infected, 35 reported getting their water from the stream, and the rest acquired their water from the well.

• 1.Calculate the relative risk for each water source (please). Round to the nearest hundredth.
  2.Which water source seems to be the source of the outbreak?
  3.How might some of the case-patients have acquired cholera without drinking from the contaminated water source?

Answer (Click to Show Hidden Text)

1. relative risk for communal well: (45/52)/(28/63)=1.95
relative risk for nearby stream: (28/63)/(45/52)=0.51
2. The well seems to be the source of the outbreak since the RR of it is higher at 1.95 compared to the stream.
3. Cholera is generally spread fecal-orally, so it could have been spread through contaminated food as well.

That is correct. The only thing I would mention is that I believe the well would be considered the source because the RR is greater than 1, not necessarily because the RR is higher than the RR of the stream. In addition, cholera may have also been transmitted when people cared for the sick, and if children played in contaminated water (although the latter is more of an issue in developing countries).

Your RR explanation makes sense, but how would you compare the two RR values if they are both greater than 1? Technically, wouldn't higher RR mean that there was "more" of an associate?

Anyway, here's the next question:
In June of 2015, there were an outbreak of 87 cases of MERS in the Samsung Medical Centre Hospital in Seoul, South Korea. The first confirmed case of MERS was Oh Sang Eun, a 35-year-old man who had just gotten back from Saudi Arabia a week earlier. 11 cases were in contact with Oh Sang Eun, and another 43 cases had been to the Arabian peninsula within 2 weeks or directly contacted someone who was exposed to MERS. Another 252 patients in the same hospital did not exhibit symptoms of MERS. The WHO traced the people these MERS patients had contacted in the past 2 weeks and 78 did not have the disease.

1. What type of study would be the most relevant for this information?
2. What type of calculation would be most relevant for this type of study?
3. Perform and intepret this calculation.

[yang573]

In June of 2015, there were an outbreak of 87 cases of MERS in the Samsung Medical Centre Hospital in Seoul, South Korea. The first confirmed case of MERS was Oh Sang Eun, a 35-year-old man who had just gotten back from Saudi Arabia a week earlier. 11 cases were in contact with Oh Sang Eun, and another 43 cases had been to the Arabian peninsula within 2 weeks or directly contacted someone who was exposed to MERS. Another 252 patients in the same hospital did not exhibit symptoms of MERS. The WHO traced the people these MERS patients had contacted in the past 2 weeks and 78 did not have the disease.

1. What type of study would be the most relevant for this information?
2. What type of calculation would be most relevant for this type of study?
3. Perform and intepret this calculation.

Answer (Click to Show Hidden Text)

-
1. This would be a (retrospective) case-control study. The population of susceptible people is not well-defined.
2. An odds ratio would be used here.
3. a = 11 + 43 = 54 b = 78 c = 87 - a = 87 - 54 = 33 d = 252
    a = 54  b = 78  c = 33  d = 252
[math]OR = \frac{ad}{bc} = \frac{54*252}{78*33} = 5.29[/math]

[dcrxcode]

In June of 2015, there were an outbreak of 87 cases of MERS in the Samsung Medical Centre Hospital in Seoul, South Korea. The first confirmed case of MERS was Oh Sang Eun, a 35-year-old man who had just gotten back from Saudi Arabia a week earlier. 11 cases were in contact with Oh Sang Eun, and another 43 cases had been to the Arabian peninsula within 2 weeks or directly contacted someone who was exposed to MERS. Another 252 patients in the same hospital did not exhibit symptoms of MERS. The WHO traced the people these MERS patients had contacted in the past 2 weeks and 78 did not have the disease.

1. What type of study would be the most relevant for this information?
2. What type of calculation would be most relevant for this type of study?
3. Perform and intepret this calculation.

Answer (Click to Show Hidden Text)

-
1. This would be a (retrospective) case-control study. The population of susceptible people is not well-defined.
2. An odds ratio would be used here.
3. a = 11 + 43 = 54 b = 78 c = 87 - a = 87 - 54 = 33 d = 252
    a = 54  b = 78  c = 33  d = 252
[math]OR = \frac{ad}{bc} = \frac{54*252}{78*33} = 5.29[/math]

All correct! Your turn

[yang573]

Here's a shorter question.

What diseases do Anopheles mosquitos transmit? What about Aedes mosquitos?

[dcrxcode]

Here's a shorter question.

What diseases do Anopheles mosquitos transmit? What about Aedes mosquitos?

Answer (Click to Show Hidden Text)

[i]Anopheles[/i] mosquitoes transmit Malaria and canine heartworm [i]Dirofilariaimmitis [/i] while [i]Aedes [/i]mosquitoes transmit Chikungunya, Dengue, ZikV, and Yellow fever.

[yang573]

Here's a shorter question.

What diseases do Anopheles mosquitos transmit? What about Aedes mosquitos?

Answer (Click to Show Hidden Text)

[i]Anopheles[/i] mosquitoes transmit Malaria and canine heartworm [i]Dirofilariaimmitis [/i] while [i]Aedes [/i]mosquitoes transmit Chikungunya, Dengue, ZikV, and Yellow fever.

Nice job. Your turn.

[dcrxcode]

Disease detectives often do several parts of an outbreak investigation at the same time.

Which of the following steps are they likely to do simultaneously?

A. Publish results of the study.
B. Interview new cases.
C. Conduct the environmental study.
D. Research similar outbreaks.
E. Identify new cases.
F. Plan the study design.