Go back

4/15

Could there be other explanations?

  • Is contact with Miss Z seven years ago the explanation for Mrs Y's infection?

  • Is the student at the nearby school linked to this cluster?

Take some time to think through your answers before checking them.

»Show answers
» Hide answers

    Feedback for Exercise 2

  • Is contact with Miss Z seven years ago the explanation for Mrs Y's infection?
  • Mrs Y’s frequent contact with Miss Z during her TB episode seven years ago is one possible explanation for Mrs Y’s recent TB infection. Mrs Y is a young female from a white British background, she has not travelled to a high incidence country, and has no other obvious risk factors for TB. However as there may have been other TB cases in the area seven years ago contact with Miss Z is not the only possible route of transmission.

    Understanding how similar the TB strains infecting Miss Z and Mrs Y are to each other will provide information which allows an estimation of the probability of transmission.

    If there is evidence to suggest that Miss Z did not transmit TB to Mrs Y contact tracing should continue in order to identify other potential sources of infection.

  • Is the student at the nearby school linked to this cluster?
  • Student B attends a nearby school; he has been diagnosed with TB around the same time as Mrs Y and six students taught by her. Student B has had no known contact with any of these cases – however he is linked in time and place, so there is some evidence he may be linked to the cluster in the school. It is also possible that student B has acquired his TB infection from a separate source and that the links in time and place have occurred by chance.

    Understanding how similar the strain of TB infecting student B is to the strains isolated from the other individuals in this cluster will provide evidence as to whether transmission is likely to have taken place or to help to rule out transmission. This will in turn inform whether investigations look at links between him and school A or concentrate on other possible sources.

    Genomics uses the whole genome sequence of the bacteria isolated from TB cases to provide high resolution information on their relatedness. Using this method would provide the information required to rule out transmission between Miss Z and Mrs Y and inform on whether student B is linked to the cluster.

» Continue