Science Page: Incidence risk and incidence rate

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week’s Science page is a follow-up from the one presented last week and focuses on the difference between incidence rate and incidence risk. Those two epidemiological measurements are often mistaken for one another.

Key points from this week edition:

  • Incidence risk is a measure of disease occurrence over a defined period of time. It is a proportion, therefore takes values from 0 to 1 (0% to 100%).
  • Incidence rate takes into account the time an individual is at risk of disease. It is not a proportion since it defines the number of cases per animal or farm time at risk.
  • Incidence risk and Incidence rate are often confused. Incidence risk and rate are numerically the same when the period at risk does not vary across individuals being studied.

Take a look at the complete report to see an example of the difference between incidence risk and incidence rate on farms.

 

Science Page: PRRS cumulative incidence by status

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

How does PRRS incidence vary based on farm status? This is the question answered in this week’s edition of the Science Page. Three different formulas were used to calculate the incidence in each of the group over type. First, the initial number of farms of each status at the beginning of the year was used as the denominator. Then, the denominator was changed to the total number of farms that entered each status since the beginning of the year. Lastly, weekly incidences calculated for each of the group since the beginning of the year were added. Calculations went back for the last 3 years.

Key points from this week edition:

  • Cumulative incidence is higher in those farms that are under status 2, 2vx and 2fvi.
  • The incidence is lower in farms that had recently an outbreak or those that are completely negative.
  • Different ways of calculating incidence by herd status lead to the same overall conclusion.

Take a look at PRRS incidences in farms of group 2 status, vaccinated or inoculated with live virus over the past years.

Science page: How farm structure and demography impact disease detection

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week’s edition reports the latest research on modeling the spread of swine vesicular diseases based on farm structure and number of sites. The model was then used to establish an expected time to detection. Two virus strains (high versus low virulence) were evaluated with the model to assess how the strain would influence the time to detection in a farm.

Key points from this week edition:

  • The models showed that the virus persisted longer in farms with a farrowing unit.
  • It is more difficult to diagnose FMD when the strains cause low mortality or no mortality.

Click on the link to see the details about disease spread models.

 

Science page: Comparing EWMAs

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

But first, we would like to congratulate our 4th-year student Hunter Baldry for receiving the ZinPro scholarship in recognition of her accomplishments as a food-animal student at the University of Minnesota. Keep up the good work, Hunter!

This week, the Science Page answers one of your questions: Is the trend of PRRSV outbreaks recorded for the original 13 participants still related to the PRRSV outbreaks evolution monitored for all the MSHMP participants?

Key points from this week edition:

  • The EWMA of the original 13 participating systems is still a good representation of the overall EWMA.
  • Questions from participants are always welcome!

Reminder: What is the EWMA?

The Exponential Weighted Moving Average (EMWA) is a statistical method that averages data over time, continually decreasing the weight of data as it moves further back in time.  An EWMA chart is particularly good at monitoring processes that drift over time and is used to detect small shifts in a trend.

In our project, EWMA is used to follow the evolution of the % of farms at risk that broke with PRRSV every week. EWMA incorporates all the weekly percentages recorded since the beginning of the project and gives less and less weight to the results as they are more removed in time. Therefore, the % of farms at risk that broke with PRRSV last week will have much more influence on the EMWA than the % of farms at risk that broke with PRRSV during the same week last year.

Take a look at the original 13 and overall EMWAs.

 

 

 

Science page: Creating really strong passwords

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project.

Last week, we explained why we took the decision to change the name of the project to honor Bob and his dedication to the swine industry. The project continues, carrying his legacy.

Key points from this week edition:

  • Computer processing power keeps increasing at an alarming rate, allowing hackers to greatly increase their password cracking capabilities.
  • Hackers’ password cracking tools can crack weak passwords in no more than a couple of hours of execution. The same tools will take millions of years to crack a strong password.
  • Whenever password cracking is mentioned in this article, it should be assumed that the password is encrypted using a strong cryptographic hash algorithm such as scrypt: http://www.tarsnap.com/scrypt.html

So what makes a strong password in the end? Read our full paper on the topic.

Science Page: Bob Morrison’s legacy

Bob_MorrisonThis is our Friday rubric: every week a new Science Page from the Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, the Science Page honors Dr. Robert Morrison, the founder and leader of the Swine Health Monitoring Project.

Bob’s unique talent for creating relationships that advanced the swine industry culminated in the creation of the Swine Health Monitoring Project (SHMP), one of the initiatives that Bob carried with pride. […] As it evolved, the SHMP changed names several times but many in the industry simply refer to it as “Bob’s project”. For that reason, and to give the just recognition he deserves, we have decided to renam the project to “Dr. Bob Morrison’s SHMP” (MSHMP).

Science page: Evaluation of positive pressure filtration to reduce aerosol transmission of PRRSV during an experimental challenge of farm access points

This is our Friday rubric: every week a new Science Page from the Swine Health Monitoring Project. The previous editions of the science page are available on our website.

Key points from this week edition:

  • Dilute vaccine aerosolization combined with novel environmental sampling techniques allowed for testing of PRRSV aerosol entry into Positive Pressure Filtration (PPF) farm access points.
  • Under the experimental conditions of this study, positive pressure air speeds >1.85m/s resulted in no aerosol transmission.
  • Ensuring adequate positive pressure air speed through steps taken to increase access point pressure can further reduce the risk of aerosol PRRSV transmission on PPF farms.

The full report on positive pressure filtration and PRRSV transmission via aerosols is available.