<span style="color: #222222;">The US President Joe Biden has again tested positive for Covid-19.  His doctor has described it as a rebound infection. In a letter describing the situation, Mr Biden's physician Dr Kevin O'Connor said there was no need to resume treatment but the president would remain under close observation.<br />''<br />'' The president was tested negative for the virus four times between Tuesday and Friday last week.  The 79-year-old first contracted the virus on 21st  July, when he was revealed to be experiencing mild symptoms. </span><br />