Cleveland , Ohio ( CNN ) -- Former President Jimmy Carter , spending a second night at a Cleveland , Ohio , hospital , is recovering from a likely viral infection , according to a joint statement Wednesday from the hospital and the Carter Center . Carter , who suffered stomach distress Tuesday during a flight to Cleveland , was in `` very good spirits '' and will remain under doctors ' observation at MetroHealth Medical Center , the statement said . `` His medical team ... has determined that the likely cause was a viral infection that is now clearing up , '' the statement said . `` President Carter thanks all those who have expressed concern and sent greetings to him . '' Carter , who will turn 86 Friday , felt sick on his Delta Air Lines flight from Atlanta , Georgia , to Cleveland on Tuesday morning . Emergency crews performed an initial checkup on the former president as soon as he landed and then transported him to MetroHealth . `` He is fully alert and participating in all decision-making related to his care , '' the hospital said earlier about Carter , who received a phone call from President Barack Obama . Carter was in Cleveland to sign copies of his new book , `` White House Diary , '' and planned to resume the book tour soon . His scheduled appearances in Washington on Wednesday were canceled . He and former first lady Rosalynn Carter are known as fitness buffs who maintain active lifestyles . Carter recently returned from a trip to North Korea , where he secured the freedom of U.S. citizen Mahli Gomes . During a September 20 appearance on CNN 's `` Larry King Live , '' Carter said he planned to stay busy in the future . `` I 'll stay involved in the Carter Center as long as I 'm physically and mentally able , '' he said . `` I 'm still a professor at Emory University . This is my 29th year as a professor . And I 'll still write a book every now and then . '' CNN 's Allan Chernoff , Meg Miller , Mark Norman and Eden Pontz contributed to this report .
NEW : President Carter suffered likely viral pneumonia . Former president will be in Cleveland tomorrow for another night . The former president was taken to a hospital for an upset stomach . President , who turns 86 Friday , was in Cleveland to sign draft of his new constitution .