Rising antibodies in two samples taken 2-4 weeks apart also indicate infection.

A raised or rising levels can indicate past or present infection.

If the cells show changes, known as cytopathic effects, then a culture is positive, meaning the test indicates infection.

Blood donors are now asked specific and very direct questions about risk factors that could indicate possible infection with a transmissible disease.

"Is there any chance at all that this does indicate infection by the parasites?"

A blood test will also show a raised white blood cell count, indicating infection present in the system.

The lesions that appear on the leaves indicate infection.

Blood tests can determine the presence of antibodies, indicating infection with the virus.

So, in population A, a person receiving a positive test could be over 98% confident (20,000/20,392) that it correctly indicates infection.

The presence of S. aureus does not always indicate infection.