Belgian triathlete Claire Michel, who withdrew from the Paris Games mixed relay days after swimming in the River Seine for the individual event, said on Tuesday that E. Coli was not to blame for her illness.
Organisers have been testing the Seine water for elevated levels of the bacteria.
Michel's illness resulted in the Belgian team withdrawing from the triathlon relay. Details of her illness were not provided by Paris 2024 organisers or the Belgium National Olympic Committee, citing the athlete's right to privacy.
"I am gradually doing better and I returned home to Belgium today," Michel wrote on Instagram on Tuesday.
"Blood tests showed that I contracted a virus (not E. Coli). After three days of vomiting and diarrhoea, which left me quite empty, on Sunday I ended up needing more significant medical attention at the clinic (in the Olympic Village)."