Olympic champion swimmer Cameron van der Burgh is perhaps facing his toughest opponent yet the coronavirus .

Van der Burgh, who won gold for South Africa in the 100 meter breaststroke in the 2012 London Olympics and silver in the 2016 Rio games, tweeted Sunday that he had contracted COVID-19 and was struggling, despite his fitness and age.

I have been struggling with Covid-19 for 14 days today, he wrote. By far the worst virus I have ever endured despite being a healthy individual with strong lungs (no smoking/sport), living a healthy lifestyle and being young (least at risk demographic).

The 31-year-old athlete complained of serious fatigue and an unshakeable cough. Any physical activity like walking leaves me exhausted for hours, he wrote.