Aru's Astana team explained he has been struggling with acute bronchitis and a fever in recent days. Cyclingnews understands that Aru's build-up to the Giro d'Italia is unlikely to change as a result of abandoning Tirreno-Adriatico. He is due to attend a training camp at Sierra Nevada ahead of his only remaining stage race before the Giro, the Tour of the Alps (formerly the Giro del Trentino) from April 17-21.
"I have to abandon Tirreno with regret because I haven't been very well for a few days," Aru said in a short video released by Astana on Sunday morning. "I tried to hang tough but this morning I was feeling worse again so the right thing to do was to stop and regain a bit of energy. I'm sorry for my team because they gave everything these last days."
Aru conceded 4:49 to Nairo Quintana (Movistar) on the Terminillo finish on Saturday after struggling on the early slopes before being dropped definitively 5.5 kilometres from the summit.
"I was really struggling because of the cough I've had for the last few days, which I had preferred to keep to myself," Aru told Gazzetta dello Sport afterwards. "In any case, I admit that I thought it would go better.
"Nobody died. It was my objective to do well in this race, but sometimes you have to take into account little seasonal bugs, which you pay for at this level. Still, it's better now than at the Giro."
Aru began his 2017 season with a strong showing at the Tour of Oman, where he placed third overall after finishing second on Green Mountain. The Sardinian went on to place 8th overall at the Abu Dhabi Tour the following week.
Winner of the Vuelta a España in 2015, Aru made an ultimately disappointing Tour de France debut last year, placing 13th in Paris. He returns to the Giro this season after placing second and third in his past two appearances in 2015 and 2014, respectively. This year's Giro gets underway in Alghero, Sardinia on May 5.