Republican White House candidate Donald Trump stole the social media spotlight during Monday night's U.S. presidential debate on at least one count — what Twitter users branded his #Trumpsniffle.

The wealthy businessman sniffed repeatedly as he faced off against Democratic rival Hillary Clinton in their first debate, giving rise to the hashtag and a surge of interest on social media what might be causing his nose to run. Parody accounts, Donald's Sinuses (@TrumpsSinuses) and Trump sniff (@TrumpSniff), gained a large following.

Trump, 70, told Fox News on Tuesday morning he did not have a cold. "No, no sniffles, no," he said. "No cold." He complained he had a faulty microphone and joked that maybe it was picking up breathing.

Several tweeters seized on the sniffling to hit back at Trump over his repeated digs at the health and stamina of Clinton, 68, who had pneumonia earlier this month.

Overall, Twitter said the debate, the first in a series ahead of the Nov. 8 election, was the most tweeted-about political event in the social media company's history. Trump was the focus of 62 percent of the conversation on the social media platform, Twitter said.

On Facebook, conversations about Trump made up 79 percent of debate chat, while Clinton's share of the conversation was 21 percent.

However, sentiment appeared to go Clinton's way. Social media analytics firm Zoomph said tweets mentioning Clinton ended at a ratio of about 1.5 to 1, which meant that for every negative mention, there were 1.5 positive mentions, Zoomph said.

Sentiment toward Trump fluctuated, but ended nearly flat at a ratio of one positive mention to every negative one.

The most tweeted-about topics were the economy, foreign affairs, energy and the environment, terrorism and guns.