Still infected status - SEP 12 Home screen - not clearing

I have noticed that the number on the "Still infected" count on SEP 12 Home page is displaying quite a number of machines and files . However,

my question is how come some infections are almost a month or 2 old and the infection status is still showing. When I check the logs for the machine,
there are no infections. How can I reset the "Still infected" count on the home screen or how long does it take to reset??